Cross Education: Possible Mechanisms for the Contralateral Effects of Unilateral Resistance Training
Authors: Lee, Michael1; Carroll, Timothy J.1
Source: Sports Medicine, Volume 37, Number 1, 2007 , pp. 1-14(14)
Publisher: Adis International
Abstract:
Resistance training can be defined as the act of repeated voluntary muscle contractions against a resistance greater than those normally encountered in activities of daily living. Training of this kind is known to increase strength via adaptations in both the muscular and nervous systems. While the physiology of muscular adaptations following resistance training is well understood, the nature of neural adaptations is less clear. One piece of indirect evidence to indicate that neural adaptations accompany resistance training comes from the phenomenon of `cross education', which describes the strength gain in the opposite, untrained limb following unilateral resistance training. Since its discovery in 1894, subsequent studies have confirmed the existence of cross education in contexts involving voluntary, imagined and electrically stimulated contractions. The cross-education effect is specific to the contralateral homologous muscle but not restricted to particular muscle groups, ages or genders. A recent meta-analysis determined that the magnitude of cross education is 7.8% of the initial strength of the untrained limb. While many features of cross education have been established, the underlying mechanisms are unknown.
This article provides an overview of cross education and presents plausible hypotheses for its mechanisms. Two hypotheses are outlined that represent the most viable explanations for cross education. These hypotheses are distinct but not necessarily mutually exclusive. They are derived from evidence that high-force, unilateral, voluntary contractions can have an acute and potent effect on the efficacy of neural elements controlling the opposite limb. It is possible that with training, long-lasting adaptations may be induced in neural circuits mediating these crossed effects. The first hypothesis suggests that unilateral resistance training may activate neural circuits that chronically modify the efficacy of motor pathways that project to the opposite untrained limb. This may subsequently lead to an increased capacity to drive the untrained muscles and thus result in increased strength. A number of spinal and cortical circuits that exhibit the potential for this type of adaptation are considered. The second hypothesis suggests that unilateral resistance training induces adaptations in motor areas that are primarily involved in the control of movements of the trained limb. The opposite untrained limb may access these modified neural circuits during maximal voluntary contractions in ways that are analogous to motor learning. A better understanding of the mechanisms underlying cross education may potentially contribute to more effective use of resistance training protocols that exploit these cross-limb effects to improve the recovery of patients with movement disorders that predominantly affect one side of the body.
____________________________________________________________________________________
The conclusion here supports the contention that teaching a patient to lift with a "rigid" lumbar posture perhaps needs to be re-thought...sound familiar?
Biomechanics of Changes in Lumbar Posture in Static Lifting.
Biomechanics
Spine. 30(23):2637-2648, December 1, 2005.
Arjmand, Navid MSc; Shirazi-Adl, Aboulfazl PhD
Abstract:
Study Design. In vivo measurements and model studies are combined to investigate the role of lumbar posture in static lifting tasks.
Objectives. Identification of the role of changes in the lumbar posture on muscle forces, internal loads, and system stability in static lifting tasks with and without load in hands.
Summary of Background Data. Despite the recognition of the causal role of lifting in spinal injuries, the advantages of preservation or flattening of the lumbar lordosis while performing lifting tasks is not yet clear.
Methods. Kinematics of the spine and surface EMG activity of selected muscles were measured in 15 healthy subjects under different forward trunk flexion angles and load cases. Apart from the freestyle lumbar posture, subjects were instructed to take either lordotic or kyphotic posture as well. A kinematics-based method along with a nonlinear finite element model were interactively used to compute muscle forces, internal loads and system stability margin under postures, and loads considered in in vivo investigations.
Results. In comparison with the kyphotic postures, the lordotic postures increased the pelvic rotation, active component of extensor muscle forces, segmental axial compression and shear forces at L5-S1, and spinal stability margin while decreasing the passive muscle forces and segmental flexion moments.
Conclusion. Alterations in the lumbar lordosis in lifting resulted in significant changes in the muscle forces and internal spinal loads. Spinal shear forces at different segmental levels were influenced by changes in both the disc inclinations and extensor muscle lines of action as the posture altered. Considering internal spinal loads and active-passive muscle forces, the current study supports the freestyle posture or a posture with moderate flexion as the posture of choice in static lifting tasks
Contralateral effects of unilateral strength training : evidence and possible mechanisms
CARROLL Timothy J. (1) ; HERBERT Robert D. (2) ; MUNN Joanne (2) ; LEE Michael (1) ; GANDEVIA Simon C. (3) ;
Author(s) Affiliation(s)
(1) Health and Exercise Science, School of Medical Sciences, University of New South Wales, AUSTRALIE
(2) School of Physiotherapy, University of Sydney, AUSTRALIE
(3) Prince of Wales Medical Research Institute, University of New South Wales, Sydney, New South Wales, AUSTRALIE
Abstract
If exercises are performed to increase muscle strength on one side of the body, voluntary strength can increase on the contralateral side. This effect, termed the contralateral strength training effect, is usually measured in homologous muscles. Although known for over a century, most studies have not been designed well enough to show a definitive transfer of strength that could not be explained by factors such as familiarity with the testing. However, an updated meta-analysis of 16 properly controlled studies (range 15-48 training sessions) shows that the size of the contralateral strength training effect is ∼8% of initial strength or about half the increase in strength of the trained side. This estimate is similar to results of a large, randomized controlled study of training for the elbow flexors (contralateral effect of 7% initial strength or one-quarter of the effect on the trained side). This is likely to reflect increased motoneuron output rather than muscular adaptations, although most methods are insufficiently sensitive to detect small muscle contributions. Two classes of central mechanism are identified. One involves a "spillover" to the control system for the contralateral limb, and the other involves adaptations in the control system for the trained limb that can be accessed by the untrained limb. Cortical, subcortical and spinal levels are all likely to be involved in the "transfer," and none can be excluded with current data. Although the size of the effect is small and may not be clinically significant, study of the phenomenon provides insight into neural mechanisms associated with exercise and training.
Journal Title
Journal of applied physiology ISSN 8750-7587 CODEN JAPHEV
Source
2006, vol. 101, no5, pp. 1514-1522 [9 page(s) (article)] (90 ref.)
Contralateral effects of unilateral resistance training: a meta-analysis
Auteur(s) / Author(s)
MUNN J. ; HERBERT R. D. ; GANDEVIA S. C. ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
School of Physiotherapy, The University of Sydney, Prince of Wales Medical Research Institute and The University of New South Wales, Sydney 2052, AUSTRALIE
Abstract
It is often claimed that strength training of one limb increases the strength of the contralateral limb, but this has not been demonstrated consistently, particularly in well-controlled studies. The aim was to quantitatively combine the results of other studies on the effects of unilateral training on contralateral strength in humans to provide an answer to this physiological question. We analyzed all randomized controlled studies of voluntary unilateral resistance training that used training intensities of at least 50% of maximal voluntary strength for a minimum of 2 wk. Studies were identified by computerized and hand searches of the literature. Data on changes in strength of contralateral and control limbs were extracted and statistically pooled in a meta-analysis. This approach allows conclusions to be based on a statistically meaningful sample size, which might be difficult to achieve in other ways. Seventeen studies met the inclusion criteria, and 13 provided enough data for statistical pooling. The contralateral effects of strength training reported in individual studies varied from -2.7 to 21.6% of initial strength. The pooled estimate of the effect of unilateral resistance training on the maximal voluntary strength of the contralateral limb was 7.8% (95% confidence interval: 4.1-11.6%). This was 35.1% (95% confidence interval: 20.9-49.3%) of the effect on the trained limb. Pooling of all available data shows that unilateral strength training produces modest increases in contralateral strength.
Journal Title
Journal of applied physiology ISSN 8750-7587 CODEN JAPHEV
Source
2004, vol. 96, no5, pp. 1861-1866 [6 page(s) (article)] (44 ref.)
Unilateral arm strength training improves contralateral peak force and rate of force development
Adamson, M. and MacQuaide, N. and Helgerud, J. and Hoff, J. and Kemi, O.J. (2008) Unilateral arm strength training improves contralateral peak force and rate of force development. European Journal Of Applied Physiology 103(5):pp. 553-559.
Abstract
Neural adaptation following maximal strength training improves the ability to rapidly develop force. Unilateral strength training also leads to contralateral strength improvement, due to cross-over effects. However, adaptations in the rate of force development and peak force in the contralateral untrained arm after one-arm training have not been determined. Therefore, we aimed to detect contralateral effects of unilateral maximal strength training on rate of force development and peak force. Ten adult females enrolled in a 2-month strength training program focusing of maximal mobilization of force against near-maximal load in one arm, by attempting to move the given load as fast as possible. The other arm remained untrained. The training program did not induce any observable hypertrophy of any arms, as measured by anthropometry. Nevertheless, rate of force development improved in the trained arm during contractions against both submaximal and maximal loads by 40-60%. The untrained arm also improved rate of force development by the same magnitude. Peak force only improved during a maximal isometric contraction by 37% in the trained arm and 35% in the untrained arm. One repetition maximum improved by 79% in the trained arm and 9% in the untrained arm. Therefore, one-arm maximal strength training focusing on maximal mobilization of force increased rapid force development and one repetition maximal strength in the contralateral untrained arm. This suggests an increased central drive that also crosses over to the contralateral side.
The contralateral effect after a single-leg coordinative training program
K. Oehlert - Universitätsklinikum Schleswig-Holstein, Campus Kiel, Klinik für Orthopädie, Kiel
J. Heine - Kiel
H. Krause - Kiel
D. Varoga - Kiel
H. Rieckert - Kiel
J. Hassenpflug - Kiel
Introduction
Motor coordination, especially balance abilities, is essential for joint stability and movement patterns. Recent studies have shown positive effects on the contralateral untrained side after unilateral strength training. The role of unilateral coordinative training programs has not yet been determined. The aim of the study was to evaluate the contralateral effect of a single-leg coordinative training program on the untrained side.
Material and Methods
61 healthy subjects participated in this prospective intervention study. 32 of them accomplished a four-week long comprehensive coordinative training program on the dominant leg. Training instruments were half sphere ankle discs and the Thera-Band®Stability Trainer. The remaining 29 subjects served as a control group. The coordinative abilities were tested with the Biodex Stability System®.
Results
The coordinative abilities of both the trained and untrained leg increased after the coordinative training. The increase in coordination was significant for both legs of the exercise group as measured by the Biodex Stability System®.
Discussion
Our results indicate that single-leg coordinative training has both an effect on the trained leg and the contralateral leg. It seems as though that patients practice with their non-affected leg coordinative exercises and their affected leg profits indirectly. If the results of the study were confirmed in injured individuals, patients could circumvent the negative effects of immobilization or limited weight-bearing after an injury.
Cross-training effects of a proprioceptive neuromuscular facilitation exercise programme on knee musculature
Nikolaos D. Kofotolisa and Eleftherios Kellis, a,
aLaboratory of Neuromuscular Control and Therapeutic Exercise, Department of Physical Education and Sport Science at Serres, Aristotle University of Thessaloniki, TEFAA Serres, Agios Ioannis, 62110 Serres, Greece
Twenty-three males were assigned to a PNF group (n=12) or a control group (n=11).
Interventions
The PNF program included training of the knee extensor and flexor muscles for a period of 8 weeks, exercising three times a week. PNF training included performance of knee movements through range of motion against manual resistance.
Main outcome measures
Isokinetic torque and fatigue of the knee flexors and extensors at 60, 180 and 300° s−1 were assessed prior to and immediately after the training period.
Results
Analysis of variance designs indicated that the PNF group demonstrated significant gains (9.9%) in knee extension torque of the contralateral leg. In contrast, no cross-training effects on peak flexion torque was observed.
Conclusions
Cross-training effects after PNF exercise were restricted to the knee extensor muscles. Such effects may be important when the aim of a rehabilitation program is to improve the knee extensor muscle function of an immobilized contralateral leg.
The Benefit of a Single-Leg Strength Training Program For the Muscles Around the Untrained Ankle
A Prospective, Randomized, Controlled Study
Benjamin S. Uh, MD, Bruce D. Beynnon, PhD*, Bryce V. Helie, Denise M. Alosa, MS, ATC and Per A. Renstrom, MD, PhD
McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington, Vermont
* Address correspondence and reprint requests to Bruce D. Beynnon, PhD, The University of Vermont McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, Robert T. Stafford Hall, Burlington, VT 05405-0084
Severe ankle injuries can require extended periods of immobilization that adversely affect the strength of the ankle muscles. We have investigated a single-leg strength training program of the muscles surrounding the ankle to determine if it produces a crossover benefit for the contralateral ankle muscles. Twenty subjects without any history of ankle injuries were randomly divided into a control and a training group. Both groups underwent isokinetic testing of the ankle muscles at the beginning and end of an 8-week period. The control group maintained normal activities between the tests. Half of the training group trained the dominant leg only and the other half trained the nondominant leg only for the 8-week period, three times per week. The subjects who trained the dominant leg improved peak torque values by 8.5% in the trained leg and 1.5% in the untrained leg. Similarly, the subjects who trained the nondominant leg improved peak torque values by 9.3% in the trained leg and 3.5% in the untrained leg. In contrast, the control group showed no significant change in peak torque, power, or endurance between the initial and final tests. With improvements in peak torque as high as 40% in the trained leg and a crossover benefit of 19% in the untrained leg in eccentric inversion, this strength training technique deserves further investigation in an injured population where the benefits may be more substantial.
The effect of strength training in muscle and nerve is memorized and reinforced by retraining.
Author;OMORI HAJIME(Univ. of Tsukuba, Inst. of Health and Sport Sci.) WATANABE AKIHITO(Univ. of Tsukuba, Graduate School) TSUKUDA FUMIKO(Univ. of Tsukuba, Inst. of Health and Sport Sci.) TAKAHASHI HIDEYUKI(Kokuritsusupotsukagakuse) KUME TOSHIRO(Univ. of Tsukuba, Graduate School) SHIRAKI HITOSHI(Univ. of Tsukuba, Inst. of Health and Sport Sci.) OKADA MORIHIKO(Univ. of Tsukuba, Inst. of Health and Sport Sci.) ITAI YUJI(Univ. of Tsukuba, Inst. of Clin. Med.) KATSUTA SHIGERU(Toa Univ.)
Journal Title;Japanese Journal of Physical Fitness and Sports Medicine
Journal Code:Z0388B
VOL.49;NO.3;PAGE.385-392(2000)
Pub. Country;Japan
Language;Japanese
Abstract;The purpose of this study was to prove the hypothesis that the effect of strength training is memorized and reinforced by retraining. Untrained university-age men participated in this training program. The retraining leg was subjected to 5 weeks of isometric training, 17 weeks of detraining and 5 weeks of retraining in knee extension. The contralateral training leg was subjected to 5 weeks of isometric training during the same period as the retraining phase of the retraining leg. Maximal isometric torque of knee extension increased after the 5-week training and remained at the trained level during the 17-week detraining period. Torque gain by retraining of the retraining leg was 2.6 times greater than that of the contralateral training leg. These changes in isometric torque corresponded with changes in iEMG of the vastus lateralis. The cross-sectional area of the quadriceps femoris muscie did not change with training. Results support the hypothesis that the effect of strength training is memorized and reinforced by retraining. In addition, results show that these adaptations would be explained by recruitment and rate coding of motor units. (author abst.)
“Research on the effects of motor imagery and mental training to motor performance show that repeated motor imagery can lead to increased muscular strength (Yue and Cole 1992), improvements in the learning of new motor skills, (Hall et al 92, Yaguez et al 98), and improved form it's in sports (eg Lejune et al 94). The learning effects are thought to arise at cortical programming levels of the motor system not from neural changes at the execution level.” Sleep and Dreaming Ed. Edward F. Pace-Schott. Page 98
“Yue and Cole (92) found an increase it peak abduction force by 22% when participants were asked to image maximal isometric contractions of the abductor digit minimi muscle on the little finger.” Advances in Sport Psychology ED By Thelma S. Horn, page 302.
“A classic study (well, classic to me, at least) by Yue and Cole in 1992 found that imagined finger abduction regimens increased the subjects’ strength by an average of 22%; actually doing the same regimen physically that the other test group was doing in their imaginations increased strength by an average of 30%. Enoka (1997) outlines some of the long-term neural consequences of repetitive action patterns, including effects at a wide range of levels (cellular to systemic) and locations (such as in the motor cortex, in the muscles themselves, and in related muscles). “ Neuroanthropology.net
Enoka, R. M. 1997. Neural adaptations with chronic physical activity. Journal of Biomechanics 30(5):447-55.
Yue G., and K. J. Cole. 1992. Strength increases from the motor program: comparison of training with maximal voluntary and imagined muscle contractions. Journal of Neurophysiology 67(5): 1114-23.
The effect of short-term strength training on human skeletal muscle: the importance of physiologically elevated hormone levels
Authors: Hansen S.1; Kvorning T.1; Kjær M.2; Sjøgaard G.3
Scandinavian Journal of Medicine & Science in Sports, Volume 11, Number 6, December 2001 , pp. 347-354(8)
Abstract:
The effect of strength training and endogenously elevated hormone levels (plasma testosterone, growth hormone (GH) and cortisol) was studied in 16 young untrained males, divided into an arm only training group, A, and a leg plus arm training group, LA, in order to increase circulating levels of anabolic hormones. Both groups performed the same one-sided arm training for 9 weeks, twice a week. Group A trained only one arm (AT), the contralateral arm serving as control (AC), whereas group LA additionally trained their legs following the training of the one arm (LAT), with the contralateral arm serving as control (LAC). In spite of the attempt to match the two groups, the initial isometric arm strength was 20–25% lower for group LA compared to group A (significant for the arm to be trained). Isometric strength increased significantly in LAT and LAC by 37% and 10%, respectively, while the 9% and 2% increases in AT and AC, respectively, remained insignificant. Isokinetic strength increased at one out of three velocities tested for the trained arm relative to the untrained arm in both group A and group LA (P<0.05). Functional strength increased significantly by 20% in LAT, 18% in LAC, 19% in AT, and 17% in AC. Hormonal responses were monitored during the first and last training sessions. Resting hormone levels remained unchanged for both groups. However, during the first training session plasma testosterone as well as plasma cortisol increased significantly in group LA but not in group A. Plasma GH rose in all exercise tests, except during the last test in group LA, but was significantly higher in group LA than in group A in the first training session. In conclusion, a larger relative increase in isometric strength was found in the group having the highest hormonal response. However, due to the initial difference in isometric strength caution must be taken with the interpretation of this finding, which may only indicate a possible link between anabolic hormones and muscle strength with training.
Neuro-Physiological Adaptations Associated with Cross-Education of Strength Journal Brain Topography
ISSN 0896-0267 (Print) 1573-6792 (Online)
Volume 20, Number 2 / December, 2007, Pages 77-88
Subject Collection Biomedical and Life Sciences
SpringerLink Date Friday, October 12, 2007
Jonathan P. Farthing1 , Ron Borowsky2, Philip D. Chilibeck1, Gord Binsted1 and Gordon E. Sarty2(1) College of Kinesiology, University of Saskatchewan, 87 Campus Drive, Saskatoon, SK, Canada, S7N 5B2
(2) Cognition and Neuroscience Programs, Department of Psychology, College of Arts and Science, University of Saskatchewan, Saskatoon, SK, Canada
Abstract Cross-education of strength is the increase in strength of the untrained contralateral limb after unilateral training of the opposite homologous limb. We investigated central and peripheral neural adaptations associated with cross-education of strength. Twenty-three right-handed females were randomized into a unilateral training group or an imagery group. A sub-sample of eight subjects (four training, four imagery) was assessed with functional magnetic resonance imaging (fMRI) for patterns of cortical activation during exercise. Strength training was 6 weeks of maximal isometric ulnar deviation of the right arm, four times per week. Peak torque, muscle thickness (ultrasound), agonist–antagonist electromyography (EMG), and fMRI were assessed before and after training. Strength training was highly effective for increasing strength in trained (45.3%; P < 0.01) and untrained (47.1%; P < 0.01) limbs. The imagery group showed no increase in strength for either arm. Muscle thickness increased only in the trained arm of the training group (8.4%; P < 0.001). After training, there was an enlarged region of activation in contralateral sensorimotor cortex and left temporal lobe during muscle contractions with the untrained left arm (P < 0.001). Training was associated with a significantly greater change in agonist muscle EMG pooled over both limbs, compared to the imagery group (P < 0.05). These results suggest that cross-education of strength may be partly controlled by adaptations within sensorimotor cortex, consistent with previous studies of motor learning. However, this research demonstrates the involvement of temporal lobe regions that subserve semantic memory for movement, which has not been previously studied in this context. We argue that temporal lobe regions might play a significant role in the cross-education of strength.
Neural mechanisms are the most important determinants of strength adaptations.
Proposition for Debate - by Amanda Broughton
Introduction
This debate addresses factors influencing an increase in muscle strength. This debate can be simply affirmed by the fact that we have all witnessed improvement in performance of a repeated strength test without evidence of muscle hypertrophy. Two definitions to clarify any misunderstandings are:
Strength
"The greatest amount of force that muscles can produce in a single maximal effort" (Lamb, 1984).
Neural mechanisms
"motor unit activation (recruitment, discharge rate), synchronization, and cross education" (Enoka and Fuglevand, 1993).
Literature suggests that physical training causes adaptations in the brain and spinal cord and that the ability of humans to recruit motor units increases with training (Lamb, 1984). Neural factors involved in muscle strength are: activation of motor units (frequency and quantity), involvement of afferent and efferent pathways, synchronization, and cross-education.
In addition to neural factors, we must consider other factors involved in muscle strength. Increased muscle cross sectional area (CSA) has a strong relationship with muscle strength (Lamb, 1984). Muscle length, rate of change of muscle length, and the alignment of the muscle with respect to the axis of joint rotation (Enoka and Fuglevand, 1993) are also involved in determining the strength of a muscle upon testing.
Background Knowledge
Considering all factors influencing muscle strength, it is important to ensure that a standard test procedure is used to evaluate muscle strength. As such, a maximal voluntary isometric contraction (MVIC) is the preferred option (Rutherford and Jones, 1986, cited in Enoka and Fuglevand, 1993). This minimizes the influence of neural components associated with muscle co-ordination, and removes influence from rate of change of a muscle. It also requires that muscle length and joint position are the same for each test. Mechanical and electromyographic (EMG) measurements are taken during the contraction to evaluate changes to the neuromuscular apparatus. EMG measurements are used as an indicator of motor unit activity, which gives an indication of the muscle force generated (Enoka and Fuglevand, 1993. Komi (1986) points out that the EMG recordings do not indicate whether the increased motor unit activity comes from the cortical or reflex sources, or from both.
Lawrence and DeLuca (1983, cited in Enoka and Fuglevand, 1993), suggest that EMG measurements during a MVIC are known to be somewhat unreliable. Howard and Enoka (1991, cited in Enoka and Fuglevand, 1993) found that on three repetitions of a knee extensor MVIC the average EMG varied substantially while the force remained constant. The authors therefore cautioned against using EMG as a direct representation of the activation of motor units of a muscle at high forces such as during an MVIC. The EMG recordings from surface electrodes are a result of summation of randomly occurring action potentials from numerous motor units. According to an unpublished dissertation by Fuglevand (1989, cited in Enoka and Fuglevand, 1993, p222), a motor unit action potential is influenced by:
the number and size of fibers innervated by the motor unit,
the spatial orientation of the fibers relative to the electrode,
the electrode configuration and dimensions,
the conduction velocity of the fiber action potential,
the spatial relationship of the electrode to the innervation zone, and the length of the muscle fibers.
Neural Mechanisms
The motor unit consists of the motor nerve cell (neuron) that originates in the spinal cord (indicated by '3' in figure 1) and all the muscle fibers it supplies. All fibers in a motor neuron are of the same fiber type and are distributed throughout the muscle (Lamb, 1984). Slow twitch fibers are usually recruited first, and once a motor unit is activated, all muscle fibers in that unit are activated equally. To modulate muscle force, motor units change their firing frequency, and the number of active motor units changes. The motor units do not all fire in unison, except under conditions of maximal stimulation. "The CNS remains capable of fully activating all motor units to respond with maximum force under conditions of extreme contractile failure" (Thomas, Woods, and Bigland-Ritchie 1989, p. 1835, cited in Enoka and Fuglevand, 1993).
A motor unit is influenced by reflex pathways, muscle spindle input, input from higher and lower spinal cord levels, and from nerves on the opposite side of the cord as shown in figure 2 (Lamb, 1984). According to Enoka and Fuglevand (1993) many authors suggest that facilitation of the MVIC is due to the descending command being supplemented with afferent feedback. Komi (1986) suggests that training intensity must be periodically varied and/or progressively increased to maintain an increase in maximal neural activation. During detraining, or immobilisation, the neural input is decreased resulting in a decreased force production and muscle atrophy.
Research Findings
Muscle Strength
Significant gains in muscle strength have been shown following short periods of resistance training, which are generally regarded as being too short to elicit morphological changes in the muscle (Moritani and deVries, 1979). It would therefore seem that this strength increase is due to an ability to better activate the muscle. Over time the muscle activation plateaus and CSA increases, suggesting that after a time, hypertrophy is the more significant factor in increased strength. Various suggestions regarding these two factors are explored below. (See Figure 3).
Neural Adaptation
"Neural adaptation after resistance training has been inferred on the basis of several studies reporting increases in muscle strength with little or no change in cross sectional area of the muscle." (Bandy et al, 1990, p.252). Most research into neural adaptations after resistance training looks mainly at motor unit activation by using EMG. It is widely accepted that increases in EMG is a result of increased firing frequency of motor units in combination with an increased recruitment of motor units.
Cross education is evidenced by an increased strength in the contralateral limb and is likely due to cross talk between nerves in the spinal cord from one side to the other. Moritani and deVries (1979) reported an increase in MVIC force of 36% in isometrically trained elbow flexors versus a 25% increase in the contralateral untrained limb. The changes in the untrained limb occurred without changes in CSA or enzyme activities. Butler and Darling (1990, cited in Enoka and Fuglevand, 1993) found an increase in EMG in the contralateral untrained limb. Subjects have exhibited a lower single limb MVIC when both limbs are active simultaneously than when tested in isolation (Howard and Enoka, 1991, cited in Enoka and Fuglevand, 1993). It could be postulated that this is due to cross talk from the contralateral side during a single limb effort that is not present to the same extent during a bilateral task.
Research Update - New Findings
Central Nervous System
Increases in strength have been shown when a subject shouts during exertion, or if a pistol is fired near the subject shortly before the test procedure (Ikai and Steinhaus, 1961, cited in Lamb, 1984). Similar strength changes have also been noted when the subject is given hypnotic suggestions of strength (Morgan, 1972, cited in Lamb, 1984). Yue and Cole (1992, cited in Enoka and Fuglevand, 1993) observed an increase in MVIC and EMG following imagery.
Electrical stimulation
It has been shown that a voluntary contraction is not a strong as a contraction stimulated electrically (Ikai and Yabe, 1969, cited in Lamb, 1984, and Stephens and Taylor, cited in Lamb, 1984).
Electrical stimulation - training
It has been shown that strength development can be achieved through electrical stimulation of a muscle, however the strength gains from this method of training are less than those noted in a voluntary training program (Massey, 1964, cited in Moritani and deVries, 1979, and Nowakowska, 1962, cited in Moritani and deVries, 1979). This is likely due to the lack of involvement of the motor pathways in electrically stimulated training. Lyle and Rutherford (1998) however, found no significant difference between strength gains in adductor pollicis of voluntary versus stimulated contractions. The large gains shown in stimulated training argues against central adaptations as a major contributor to the strength increases following training.
EMG
In most studies, the EMG/force slope initially remained the same as in the pre-trial testing with an increase in muscle activation (EMG values). After a few weeks resistance training the EMG slope started to decrease, indicating muscle hypertrophy gradually becoming integrated in the strength increase and the rapidly increasing muscle activation slowed to a lesser rate.
Disproportionate CSA increase
After a number of weeks of resistance training, an increase in CSA can be measured. This increase is proportionally smaller than the increase in MVIC (Narici et al, 1989, cited in Enoka and Fuglevand, 1993). Nonetheless, CSA is the single best predictor of muscle strength. Larger muscles have a greater amount of actin and myosin, therefore a greater number of cross bridges, which results in a greater potential for force production during contraction.
Motor Unit Synchronisation
Strength training can increase motor unit synchronization. Friedeboldet et al (1957, cited in Komi, 1986) was among the first to suggest that, in particular, the early part of strength training is associated with an increase in motor unit synchronization. Komi goes on to suggest two possible explanations for this increased synchronization.
The dendrites of alpha-motor neurons receive increased input from sensory fibers, and
The higher motor centers increase their descending activity.
Specificity
Rasch and Morehouse (1957, cited in Moritani and deVries, 1979) demonstrated strength gains from a six-week training program in tests where muscles were used in a familiar way, but not when unfamiliar test procedures were involved. This suggests that larger test results were mainly due to skill acquisition.
Muscle Hypertrophy
Muscle hypertrophy seems mostly to result after training periods greater than six weeks, and is predominantly related to fast rather than slow twitch fibers (Bandy et al, 1990). Komi (1986) suggests that the increased alpha-motor neuron activation with motor neuron synchronization may stimulate hypertrophic factors that are expected to result after a period of progressively increasing strength training.
Clinical Implications
When considering a resistance training program, it is important to understand what you are improving at various stages of the program. Initially improvement will be due to neural adaptation. To maximise this potential, the program needs to be modified and/or progressed regularly so that neural adaptation does not plateau too soon. It is also necessary to consider the phenomenon of specificity. The muscle will improve in performing the task it is trained to do, there is minimal crossover to other tasks, and so a variety of contraction modes and joint positions will need to be employed for a more comprehensive program. Ensure that the task that is being trained will have functional relevance for day-to-day living. After a time hypertrophy will become evident. To maintain muscle strength and bulk, the training program needs to continue and be progressed and modified.
The phenomenon of bilateral deficit needs to be considered. A muscle can generate a greater force if worked in isolation. Unilateral training will therefore result in a more rapid strength increase than a bilateral task. Considering specificity, it may be necessary to train both ways.
Conclusion
Initial changes to muscle strength are due to neural factors (motor unit activation, firing frequency, input from the opposite side of the spinal cord, input from muscle spindles and reflexes, input from lower and higher spinal cord levels). Over time, the increased rate of neural activation decreases to a slower rate and muscle hypertrophy commences (this is postulated to be stimulated by the neural system). The muscle CSA increases with continued training. This also results in increased strength. The CSA does not increase to the same extent as the muscle strength. The total strength increase is a combination of increased neural activation and muscle hypertrophy.
References
Bandy WD, Lovelace-Chandler V, and McKitrick-Bandy B (1990)
Adaptation of skeletal muscle to resistancetraining. Journal of Orthopaedic and Sports Physical Therapy 12(6):248-255
Enoka RM and Fuglevand AJ (1993)
Chapter 8: Neuromuscular basis of the maximum voluntary forcecapacity of muscle. In Grabnier MD (Ed): Current issues in Biomechanics.Champaign, IL: Human Kinetics Books.
Komi PV (1986)
Training of muscle strength and power: interaction of neuromotoric, hypertrophic, and mechanical factors. International Journal of Sports Medicine 7:10-15
Lamb DR (1984)
Physiology of Exercise: Responses and Adaptations (2nd ed). New York: MacMillan Publishing Company.
Lyle N and RutherfordOM (1998)
A comparison of voluntary versus stimulated strength training of the human adductor pollicis muscle. Journal of Sports Sciences 16(3):267-270 (Abstract only viewed)
Moritani T and deVries HA (1979)
Neural factors versus hypertrophy in the time course of musclestrength gain. American Journal of Physical Medicine 58(3):115-130
Plowman SA and Smith DL (1997)
Exercise Physiology: For Health, Fitness, and Performance. Boston, MA: Allyn and Bacon.
DeschenesMR, Maresh CM, and Kraemer WJ (1994)
The neuromuscular junction: structure, function, and its role in the excitation of muscle. Journal of Strengthand Conditioning Research 8(2):103-109
Higbie EJ, CuretonKJ, Warren GL, and Prior BM (1996)
Effects of concentric and eccentrictraining on muscle strength, cross-sectional area, and neural activation.Journal of Applied Physiology 81(5):2173-2181
Enoka RM (1988)
Musclestrength and its development. New perspectives. Sports Medicine 6(3):146-168
Seger JY, Arvidsson B, and Thorstensson A (1998)
Specific effects of eccentric and concentric training on muscle strength and morphology in humans. European Journal of Applied Physiology and Occupational Physiology 79(1):49-57
Zhou S (2000)
Chronicneural adaptations to unilateral exercise: mechanisms of cross education. Exerciseand Sports Science Reviews 8(4):177-184
Mindful Exercise
By CHRISTOPHER SHEA
Simply by telling 44 hotel maids that what they did each day involved some serious exercise, the Harvard psychologist Ellen Langer and Alia J. Crum, a student, were apparently able to lower the women’s blood pressure, shave pounds off their bodies and improve their body-fat and “waist to hip” ratios. Self-awareness, it seems, was the women’s elliptical trainer.
At the start of the study, Langer and Crum quizzed 84 maids at seven carefully matched hotels about how much exercise they got. Fully a third of the women said they got no exercise at all, while two-thirds said they did not work out regularly. Langer and Crum took several measures of the women’s basic fitness levels, which indicated that they, indeed, had the poor health of basically sedentary people. Then just over half the women were told an unfamiliar truth: cleaning 15 rooms daily — pushing recalcitrant vacuum cleaners, scrubbing tubs, pulling sheets — constitutes more than enough activity to meet the surgeon general’s recommendation of a half-hour of physical activity daily. The researchers even provided specifics: 15 minutes of scrubbing burns 60 calories, 15 minutes of vacuuming burns 50. The basic message and the details were then posted in the maids’ lounges in the hotels where the 44 women worked, to serve as reminders, while a control group was left in the dark.
A month later, Langer and Crum checked back with the women to find, as they reported in the February issue of Psychological Science, remarkable results. The average study-group maid had lost 2 pounds, while her systolic blood pressure had dropped by 10 points; by all measures the 44 women “were significantly healthier.” Yet there were no reported changes in behavior, only in mind-set, with the vast majority of the women now considering themselves regular exercisers. Langer sees the study as a lesson in the importance of mindfulness, long a subject of her research, and which need not involve Buddhism or meditation, she stresses. “It’s about noticing new things; it’s about engagement,” she says.
But for the study’s white-collar readers, a corollary to its results might be dispiriting: Made freshly aware — mindful — of just how sedentary their work lives are in contrast to a housekeeper’s, might they not suffer a corresponding decline in health?
____________________________________________________________________
Healthy mind, healthy body
· Saturday August 23 2008
Belief is half the battle with housework.
What I particularly enjoy is the spectacle of fat people - ideally drinking beer - watching television, while somewhere on the other side of the world citizens of all nations are getting some nice exercise in the Olympics (throwing javelins, jumping over metal bars, climbing lamp-posts with banners, and running away from the water cannon).
These are the people I imagine paying for gyms they never visit, while I am cheerfully cycling to work and carrying the shopping up the stairs.
But can obsessing over sport actually improve your health? Slightly, possibly, if you've got something to work with.
Alia Crum and Ellen Langer from Harvard psychology department took 84 female hotel attendants in seven hotels. They were cleaning an average of 15 rooms a day, each requiring half an hour of walking, bending, pushing, lifting, and carrying. These women were clearly getting a lot of good exercise, but they didn't believe it: 66.6% of them reported not exercising regularly, and 36.8% said they didn't get any exercise at all.
Their health, measured by things such as weight, body fat, body mass index, waist-to-hip ratio and blood pressure, was related to their perceived amount of exercise, rather than the actual amount of exercise they got, and this, so far, isn't very unusual.
A classic study of 7,000 adults found that perceived health is a better predictor of death than actual health, and another looking at elderly people found that those who perceive their health to be poor are six times more likely to die than those who perceive their health to be excellent, regardless of how healthy they actually are. Once again this goes to show the danger of relying on self-report data for health research.
But it gets better. Crum and Langer then divided the hotel workers into two groups (by hotel). One group got a one hour presentation on what a fabulous amount of exercise they were getting, how they were meeting and clearly exceeding recommendations for an active lifestyle.
They were given information sheets, in English and Spanish, showing the calorie burn for activities like vacuuming, or cleaning a bathroom, and the researchers even put notices up in communal areas explaining what excellently healthy exercise their work was. The other group was left alone.
Four weeks later the researchers measured everything again. The group who had been tutored about the health benefits of their work now perceived that they did more exercise than before - unsurprisingly - while the group who were left alone didn't change. Neither group had changed their actual levels of activity.
But amazingly, despite no change in actual exercise levels, in the intervention group, simply being told about the value of what they were already doing caused a significant change for the better on every single one of the objective health measures recorded: weight, body fat, body mass index, waist-to-hip ratio and blood pressure.
It's an outrage. Maybe mindset alone can influence metabolism and the benefits of exercise: perhaps this experiment shows, essentially, the placebo benefits of exercise. Maybe the cleaners changed their behaviour, or their diets, in ways that the researchers didn't pick up, perhaps they had more spring in their step, tipping the scales in their favour. And maybe it doesn't actually matter what caused the change, as long as we can exploit it: because the links between body and mind are far more fascinating than any pill peddler would ever have you believe.
· Ben Goldacre's Radio 4 documentary series Placebo is available online at
qurl.com/placebo
Training with unilateral resistance exercise increases contralateral strength
Joanne Munn,1 Robert D. Herbert,1 Mark J. Hancock,1 and Simon C. Gandevia2
1School of Physiotherapy, The University of Sydney, Lidcombe; and 2Prince of Wales Medical Research Institute, University of New South Wales, Randwick, Australia
Submitted 11 May 2005 ; accepted in final form 10 July 2005
Evidence that unilateral training increases contralateral strength is inconsistent, possibly because existing studies have design limitations such as lack of control groups, lack of randomization, and insufficient statistical power. This study sought to determine whether unilateral resistance training increases contralateral strength. Subjects (n = 115) were randomly assigned to a control group or one of the following four training groups that performed supervised elbow flexion contractions: 1) one set at high speed, 2) one set at low speed, 3) three sets at high speed, or 4) three sets at low speed. Training was 3 times/wk for 6 wk with a six- to eight-repetition maximum load. Control subjects attended sessions but did not exercise. Elbow flexor strength was measured with a one-repetition maximum arm curl before and after training. Training with one set at slow speed did not produce an increase in contralateral strength (mean effect of –1% or –0.07 kg; 95% confidence interval: –0.42–0.28 kg; P = 0.68). However, three sets increased strength of the untrained arm by a mean of 7% of initial strength (additional mean effect of 0.41 kg; 95% confidence interval: 0.06–0.75 kg; P = 0.022). There was a tendency for training with fast contractions to produce a greater increase in contralateral strength than slow training (additional mean effect of 5% or 0.31 kg; 95% confidence interval: –0.03–0.66 kg; P = 0.08), but there was no interaction between the number of sets and training speed. We conclude that three sets of unilateral resistance exercise produce small contralateral increases in strength.
The Shocking Nervous System!
by Chad Waterbury
Within the realm of training for greater strength, muscle mass, and endurance lies an area of science that remains relatively untapped: Neuroscience. It's indeed the uncharted waters in the vast ocean of the science and practice of resistance training. That's because so little is known about how the nervous system actually works.
Indeed, neuroscientists have yet to figure out how information in your brain is stored, processed, and retrieved. What exactly does that mean, anyway? It means we're not sure how your brain stores the phone number from that busty fitness bunny you met at the gym.
And when you need to recall her number because your old man left you the keys to his lime green Prius, we don't know how your brain is doing it. A few neuroscientists have a few muddy ideas, but there are still too many unknowns to clean and jerk those neural processes out of ambiguity.
So it's not surprising to learn that little is known about the relationship between the nervous system's control of skeletal muscle and how we can improve its function to build bigger muscles and bigger lifts.
But don't fret yet, Brett. Neurologists have accumulated a pretty respectable sample of studies over the last 50 years that help elucidate just how damn powerful your brain, spinal cord, and associated neurons really are to control and develop your strength and muscles. So I'm here to take you through some landmark neuroscience studies that make me drool like a perv at a peepshow.
I drool, yes I do. I drool because I know the next few decades are going to uncover my postulate that the nervous system is what's holding us back from developing strength and muscle beyond our wildest dreams.
Why I Believe The Nervous System is the Key
1. Nerve Controls Muscle — You have muscles that are classified as fast or slow. These muscles are matched up with nerves that are either fast or slow, too. So, by nature, a fast muscle has a fast nerve, and a slow muscle has a slow nerve.
But what happens when you pull a fast nerve out of its muscle and insert the fast nerve into a slow muscle? The muscle takes on fast characteristics. Voila! This process, known as cross innervation, demonstrates that nerve controls muscle. We can thank Eccles and his colleagues, along with Salmons and Sreter, for these demonstrations because their studies are probably the most significant demonstrations of the power that nerves have over muscles. (1, 2)
It wasn't, however, until 1998 before this concept was taken a step further. Before I get to the next study and what it demonstrated, I want to give you a brief lesson in the physiology of muscle hypertrophy.
New proteins that cause hypertrophy are produced in the nucleus of your muscle cells. The intent of resistance training is to break down muscle proteins so your body will send a signal to create more proteins. Over the course of months, this creation and insertion of new proteins in your muscles is what causes visible muscle growth. And what enters the nucleus to signal new protein formation is known as a transcription factor.
In 1998, Chin et al demonstrated that the rate of nerve firing into the muscle determined whether fast or slow muscle proteins were formed. During periods of slow nerve activity, a specific transcription factor (NFAT) enters the nucleus and induces slow fiber formation. (3) My iteration is this: when NFAT enters the nucleus of a muscle, slow fibers are formed.
In a fast muscle, its fast nerve activity keeps this same transcription factor (NFAT) from entering the nucleus. The result? Slow muscle fibers aren't formed and the fast muscle can keep making more fast muscle fibers. That's good because fast muscles can produce more force, and they're thought to grow larger than slow muscles.
In essence, the Chin et al study demonstrated why slow nerves and slow muscles go together, and why fast nerves and fast muscles go together (their nerve activity is correlated with their specific muscle fiber formation). But as a philosopher, trainer, and lifter, I want to know what I can do with this information to build bigger, stronger muscles.
And this, my friends, is where I take an enormous leap of faith.
You see, I preach the importance of fast muscle contractions for a variety of reasons. One of the reasons is because of a study by Desmedt and Godaux. They demonstrated that fast muscle contractions activated motor units earlier; and fast contractions activated approximately three times as many motor units as slow contractions.(4) But I'm also taking what I learned from the previous studies and apply it to strength and hypertrophy training.
Here's What I'm Hoping the Future Will Show: Fast muscle actions cause more fast muscle fibers to be formed by blocking slow muscle fiber formation in the nucleus, thus allowing us quicker strength and muscle gains.
Early Intermission
Up to this point, I attempted to explain what happens when you switch nerves and muscles. And I touched on what type of muscle proteins are formed in response to slow or fast nerve activity. Those are direct correlations between nerve and muscle.
This next section, however, touches on the relationship between strength gains that occur in muscles that aren't even stimulated by their associated nerves. In other words, if you really want to see some amazing demonstrations for the power of your brain, the power of your neighboring muscles, and the power of your central nervous system, keep reading.
2. Our Brain Makes our Muscles Stronger — My all-time favorite neuroscience study was performed by Yue and Cole in 1992. I carry this study around with me like Ben Affleck must carry around his Oscar from Good Will Hunting. When I'm feeling hungry or lonely, I suckle on the page corners like a newborn pig suckles on his mama's tit. And once while in a state of inebriation, I put a wig on it and... .okay, I better stop there.
What's so mesmerizing, alluring, and radical about the Yue and Cole study? Well, they had two groups of people "perform" a strength training protocol. The first group trained their left hand muscles for 5 sessions per week for four weeks. Like any reputable study on strength enhancement, the movement had to be isolated and simple to eliminate other complex variables that occur with larger motor tasks. Basically, they abducted their left pinky finger against resistance.
Powerful pinky!
The other group? They imagined doing the same movement with the same effort and frequency. Yes, you read that right: they simply thought about the exercise, but didn't move a muscle. And just to make sure that they didn't move a muscle, the researchers hooked them up to an EMG to make sure they weren't producing any force whatsoever.
Now, for the shocking part: At the end of the study, the group that actually performed the contractions against resistance increased their strength by 30%. But the "imagined contraction" group increased their strength by 22%! (5)
I still get chills when I think about what that study demonstrates.
This is about as close to a holy grail as a neurophysiologist like me will ever find. I mean, think about that protocol and its implications. It means that we can significantly improve our strength without even contracting our muscles!
How does this happen? We really don't know. Remember what I said in the beginning, there's so much we don't know about even the most common neural tasks such as storing and recalling memories. But it's likely that by thinking about a specific movement, we're priming our descending pathways so our muscles at the end of the pathway will receive more stimulation (greater motor unit recruitment) once we actually perform the movement.
Then again, the adaptation could be limited to our higher brain centers. A committee of brain areas work together before sending a signal down your spinal cord and out to your muscles. That "committee" might get stronger when we think about a movement on a regular basis. We really don't know, but we know that our mind can improve our strength.
How To Apply This Information: It probably goes without saying, but you should make an effort to think... I mean, really think through the lifts you're trying to improve the most. When you're not in the gym, think about your squat, deadlift, bench press, and clean and jerk form. Think about the form for whatever movements you need to improve the most. And I'd be willing to take another leap of faith and say that by imagining your movements outside of the gym in a quiet room, it might help you add mass.
Want bigger calves? Train them hard, fast, and heavy in the gym. And when you're not in the gym, take time during the day to really concentrate on the calf movements you perform. With your mind focused, feel the burn in your calves, imagine the load on your calves, and picture your calves growing. The greatest bodybuilders and trainers often point to the power of the mind for building bigger, stronger muscles. These imagined contractions could very well be one of the keys. I believe that such imagined contractions will augment your results in the gym.
3. You Can Get Significantly Stronger without Getting Bigger — We all want to be big and strong. Some of us are genetically blessed with lots of muscle mass, and others (including this writer) must cuss, scream, and bleed their way to every ounce of new muscle. But one thing's for certain: we all know we can get much stronger without getting bigger. And this is an important key to understanding the nervous system.
One of the top neuroscientists in the field of motor unit recruitment and strength adaptations is Dr. Roger Enoka. Here's what he had to say about the relationship between strength and muscle size:
"Although the maximal force which a muscle can exert is directly related to its cross-sectional area, there is a poor correlation between increases in strength and muscle size." (6)
Here's how I translate what he said: If you take two, untrained 25 year-old males and test their maximal strength, it's likely that the guy who has naturally bigger quadriceps will be able to produce more force in a leg extension test. But if you compare the size of the quadriceps between two, highly-trained 25 year-old males, their size won't determine who's stronger.
That's because strength is a complex entity that's affected by neural, mechanical and muscular factors. In other words, out of the three factors that can increase strength, only one is dependent on hypertrophy, and even that's debatable. It appears you can augment muscular factors that increase strength but aren't necessarily dependent on hypertrophy. What I'm referring to are proteins that attach your contractile proteins to the Z-disc of your muscle's sarcomere.
How to Apply this Information: My position is that you should always strive to improve your performance in the gym. If you're not providing a new, challenging stress by attempting to add more weight, lift faster, and/or increase the training volume, you won't build bigger and stronger muscles.
Training for maximal strength is a great way to add more muscle, but you must provide your muscles with enough training volume to elicit a hypertrophy response. After all, that's why I mentioned that there's a poor correlation between size and strength. In my view, the studies that didn't show a correlation between the two simply didn't use a high enough training volume, intensity, or frequency.
Merely getting stronger will not make you bigger. If you're training to get stronger, but you're not getting bigger, you need to eat more calories, increase your training frequency, and/or increase your training volume. I've compiled the guidelines for sufficient training volumes in my
Set-Rep Bible article.
4. We Have Brakes on our Muscles — After studying the nervous system's role in human strength and performance, I've come to this conclusion: Our nervous system has the brakes set on our muscles' capabilities. Think of a high-performance sports car: if the emergency brake is partially on, it won't be able to perform at its maximum potential. The same is true with your nervous system's control over your muscles.
Why is this so? The answer is undoubtedly more complex than any team of neuroscientists could ever uncover, but the simplest answer is probably because of protective mechanisms. Our body doesn't want to be damaged or hurt in any way, shape or form. That's why we can't help but squint and flinch when an unexpected object comes flying at our precious eyeballs. And that's why we damn near piss ourselves when someone unleashes an air horn behind us while we're reading a book. Both of those actions mimic life-threatening situations that our ancestors had to survive — actions such as dodging an oncoming raptor or running from the vicious roar of a hungry beast.
In other words, we have thousands of year's worth of survival reflex mechanisms hard-wired into our nervous system. Building bigger biceps wasn't important for survival, and neither was squatting triple your body weight. So what we must do is find ways to release the brake that our nervous system is putting on our muscles. If we do, we can tap into motor units and contractile proteins that will accelerate our size and strength beyond belief. But this "unbraking" must be gradually systematic — if it's not, we'll tear our muscles and joints to shreds.
Case in point: If your son, daughter, or mistress was trapped underneath your car, you could immediately release this brake that I'm referring to. Yep, you could probably lift up the back end of the car even though you couldn't ordinarily deadlift 600 pounds. Your brain is the commander of your nervous system, and if your brain decides that you must deadlift 600 pounds of Chevrolet to untrap your daughter, you'll be able to do it. (It's likely, however, that your lower back will remind you over the course of 3 months while you're in physical therapy.) So as I said, we must release the brake slowly.
How to Apply This Information: The first step is to find whatever motivates you to build a bigger, stronger body and constantly remind yourself of whatever it is. Studies have demonstrated that motivation causes people to immediately increase their maximal strength.(7) In other words, being motivated will help release the brake.
The next steps take place in the gym. There are two techniques that work well to ease the brake off your muscles by tricking your nervous system. The first, and one that I've discussed many times, is the supramaximal hold that causes postactivation potentiation. Check out my
Primed For Muscle article for more information.
The second option, heavy 1/4 reps, works through a similar neural mechanism. This is as simple as it sounds: lift the heaviest load you can handle for the strongest 1/4 of any movement. Keep in mind, the 1/4 portion that's naturally strongest will differ depending on what movement you're performing. Examples are the last 1/4 before lockout for the squat, deadlift, military press, dip, and bench press. For exercises such as curls, pull-ups and rows, you'll only be moving the load through the first 1/4 of flexion.
The advantage of 1/4 reps is that they allow massive loads that force your nervous system to recruit more motor units. However, no bragging rights will ever be won by doing heavy 1/4 reps for every workout. Limit 1/4 reps to one workout each week. Here's a total body routine that works great to help release the brake on your muscles.
Sets: 3
Reps: 3 reps for 1/4 of the movement
Load: The heaviest weight you can handle
Rest: 90s between movement pairings (A1, rest 90s, A2, rest 90s, A1, rest 90s, A2, etc.)
A1. 1/4 Squat
A2. 1/4 Leg Curl
B1. 1/4 Dip
B2. 1/4 Chin-up
C1. 1/4 Seated Military Press
C2. 1/4 Incline Hammer Curl
D1. 1/4 Standing Calf Raise
D2. 1/4 Romanian Deadlift
Conclusion
That's it for now. I encourage you to read through this article a few times and really think about how the nervous system controls your muscles. If you open up your mind a little and think about the studies I referenced, you'll develop a greater appreciation for the elusive nervous system and all its wonders.
1. Buller AJ, Eccles JC, Eccles RM. J Physiol (Lond) 150:419, 1960.
2. Salmons S, Sreter FA. Nature 263:30-34, 1976.
3. Chin et al. Genes Dev12:2499-2509, 1998.
4. Desmedt JE, Godaux E. J Physiol 264:673-693, 1977.
5. Yue G, Cole KJ. J Neurophysiol 67(5):1114-1123, 1992.
6. Enoka R. Sports Med6:146-168, 1988.
7. Bigland-Ritchie B. Clinics in Chest Medicine 5:21-34, 1984.
© 1998 — 2006 Testosterone, LLC. All Rights Reserved.
November 2003
Strength in Practice By Rhonda Kotarinos, PT
Urinary incontinence is one of the most common health problems affecting women in America. It is estimated that 30% to 50% of community-dwelling older women experience urinary incontinence.1,2 In women age 18 and older, the prevalence of incontinence is estimated to be 8.5% to 47%.3 Treatment options to be considered for managing urinary incontinence should initially be the least invasive, with the fewest possible adverse complications, and should be individualized for the patient.4 This specifically refers to behavioral techniques for treating urinary incontinence.
Behavioral techniques include assisted toileting, bladder retraining, and pelvic floor muscle rehabilitation, which includes pelvic muscle exercise, biofeedback, and pelvic floor electrical stimulation. Randomized controlled trials of behavioral management have indicated that stress and/or urge incontinent episodes can be reduced by 50% to 80% through these methods of therapy.5-8
For physical therapists, behavioral management of urinary incontinence can be divided into two approaches: pelvic floor and musculoskeletal management (see Figures 1 and 2, pages 38 and 39).
Pelvic Floor Management
The pelvic floor algorithm for behavioral management is self-explanatory. It is understood that a thorough history should be taken, followed by a thorough evaluation. Evaluation of the pelvic floor is extremely important. Simplified, the physical therapist needs to determine if the patient can actively contract the pelvic floor. Once this is determined, the therapist can then develop the appropriate treatment plan.
If there is an adequate isolated active contraction, the therapist has several treatment options, which will depend on the strength of the isolated active contraction. If the pelvic floor contraction is of a trace or poor grade, the therapist may utilize facilitation, active assistive exercise, overflow, or biofeedback.
Neurophysio-logical facilitation techniques that could be used include quick stretch, tapping, and/or proprioceptive neuromuscular facilitation (PNF).
Resistance to the PNF diagonal of extension, adduction, and external rotation neurophysiologically facilitates a pelvic floor contraction. To see this normal function in action, look at the local playground where children can be seen standing with their legs crossed at the ankles in an isometric contraction of extension, adduction, and external rotation in hopes of getting the pelvic floor to send a stronger signal to the bladder.
Physical therapists are quite familiar with the theory of therapeutic exercise. When treating a muscle that is below a fair grade of strength, they utilize positions of gravity eliminated or assisted to exercise a muscle of poor or trace strength, respectively. When the pelvic floor is strong enough, progressive resistive exercise would follow. Progressive resistive exercises would be accomplished with vaginal weights or a perineometer. Progressive strengthening could lead to performing various functional activities, such as stair climbing, laundry, and sports (ie, tennis, golf), with vaginal weights in place.
Cross transfer of training is another technique the physical therapist can use to enhance the strengthening process of a weakened pelvic floor. Hellebrandt described cross transfer of training more than 50 years ago.10 Hellebrandt demonstrated that strengthening exercises to a limb will increase the strength in the unexercised contralateral limb. Kannus et al not only found a transfer of muscle strength, but also discovered a transfer of power and endurance.11 Clinically, this means that the physical therapist can establish a progressive resistive, low repetition strengthening program for the hip girdle musculature and facilitate the strengthening of the pelvic floor. Initiating the strengthening process in this manner allows minimal isolated active contractions to develop without excessive inappropriate recruitment.
Once a minimal isolated contraction is present, biofeedback can be utilized to continue the strengthening process. When the pelvic floor strength is at a fair grade, treatment would continue with progressive strengthening exercises.
Electrical Stimulation
When there is no palpable active contraction, besides utilizing neurophysiological facilitation and cross transfer of training, the therapist may choose to treat with electrical stimulation. Electrical stimulation has been used to treat gynecologic disorders for well over 100 years.12 The mechanism of action in treating urinary incontinence is not well understood, but two mechanisms are described. When there is an intact neural pathway, electrical stimulation can neurally inhibit inappropriate detrusor contractions. This is the basis for utilizing electrical stimulation to treat urge incontinence. Brubaker et al, in a randomized blinded controlled study, found that electrical stimulation at a frequency of 20 Hz with a 2 second/4 second work rest cycle and a pulse width of 0.1 second cured detrusor instability (urge incontinence/urgency) in 49% of the subjects.13
The second mechanism, which addresses stress incontinence, involves electrical stimulation of neurally intact muscle, which can promote hypertrophy of the pelvic floor musculature. Increased pelvic floor strength is associated with decreased leakage and an increased ability to inhibit inappropriate detrusor contractions. Uncontrolled studies indicate that the improvement rate is 60%.
Physical therapists have the appropriate background to be more holistic in the behavioral management of urinary incontinence. There are several aspects of musculoskeletal dysfunction that can affect the treatment of urinary incontinence. They are postural dysfunction, abdominal dysfunction and generalized weakness, specifically pelvic girdle weakness. Facilitating pelvic floor strengthening with cross transfer of training by strengthening the pelvic girdle muscles has already been described.
Postural Dysfunction
Postural dysfunction has been considered a factor in pelvic floor dysfunction for almost 100 years. Goldthwaite describes in great detail how postural dysfunctions of a flat back and increased lordosis contribute to pelvic organ prolapse, which may be a factor in urinary incontinence. Goldthwaite states that “the physician has a higher function than the mere treatment of local conditions . . . . It means at once that our work must be judged upon the basis of the ultimate cure of general efficiency rather than simply the immediate relief of some local lesion. It means that in the treatment of disturbances or displacements of the pelvic organs, it is only half doing the work if the condition is simply treated locally, while an imperfect posture which may have been largely responsible for the trouble is allowed to go uncorrected.”15
In a retrospective case-control study, Lind et al found that thoracic kyphosis was associated with uterine prolapse.16 An individualized postural corrective exercise program should be developed to address the postural dysfunction noted on evaluation.
The basic tenet of the physical therapy approach to behavioral management of urinary incontinence is to improve the function of the pelvic floor through strengthening or decreasing the tone of the pelvic floor. As already described, this can include pelvic floor exercises, biofeedback, and electrical stimulation.
Other Musculoskeletal Dysfunctions
Why do only 25% to 50% of the conservatively managed patients achieve near dryness? 5-8 There are two musculoskeletal dysfunctions that can significantly impact the pelvic floor that are frequently overlooked and not treated by many health care practitioners. They are diastasis recti and the contracture of the pelvic floor. Diastasis recti is a separation of the rectus abdominis muscles at the linea alba. A weakened abdominal wall with or without a diastasis recti is an important factor in pelvic organ support. Historically, this has been referred to as the retentive power of the abdomen wall.17 Abdominal wall strength must be maintained for it to function properly in supporting the abdominal and pelvic organs. If a diastasis is present, it must be corrected before progressive abdominal strengthening is initiated. More recent research also shows that addressing the abdominal wall facilitates pelvic floor muscle coordination, support, strength, and endurance.18
The gold standard of pelvic floor exercise to treat incontinence is a Kegel or concentric exercise of the pelvic floor. Unfortunately, this may not be the most appropriate exercise for all patients with incontinence. Optimal skeletal muscle function is dependent on a length-tension relationship. The force of a muscle contraction decreases if the muscle is too long or too short.19
The goal of therapy in treating hypertonic muscles is to decrease the excessive electrical activity that is holding the pelvic floor in a shortened state. Hypertonic pelvic floor muscles can develop through protective guarding with pain or with constant recruitment to inhibit urge. In time, the elevated EMG activity will stop, leaving the pelvic floor in a new shortened position.20 In this shortened state, the pelvic floor is no longer at its optimal length-tension relationship to adequately function to inhibit urge with resulting urge incontinence, urgency-frequency syndrome, or interstitial cystitis. The shortened pelvic floor can also be a factor in stress incontinence if it cannot reflexively contract and compress the urethra when there is increased intra-abdominal pressure.
Management of the shortened pelvic floor is multifactoral. Trigger points that may be present need to be released with or without injections. Stretching is appropriate to manage trigger points as well as contractures.
Lengthening a shortened muscle is the initiation of a strengthening program. Proprioceptive neuromuscular facilitation can be utilized to assist in lengthening the shortened pelvic floor through neurological inhibition. As the pelvic floor lengthens, the patient’s proprioception improves and the patient can actively lengthen their pelvic floor from a resting position. Because of tissue memory, it may be prudent for patients who have had pelvic floor contractures to precede their concentric (Kegel) contraction with a lengthening contraction. Success rates of behavioral approaches to incontinence might improve if physical therapists consider addressing diastasis recti and pelvic floor contracture. Much more research is needed to prove that either of these two conditions has an impact on the management of urinary incontinence. Physical therapists must be made aware at least of the possibility that the association exists so that they can begin to consider the conditions in their treatment plans.
Rhonda Kotarinos, PT, is president of Rhonda Kotarinos Ltd, Oak Brook Terrace, Ill.
References
Diokno A, Brock B, Brown M, Herzog AR. Prevalence of urinary incontinence and other urological symptoms in the non-institutionalized elderly. J Urol.1986;136:1022-5.
Thom D. Variation in estimates of urinary incontinence prevalence in the community: effects of differences in definition, population characteristics and study type. J Am Geriatr Soc. 1998;46:473-80.
Herzog AR, Fultz NH. Prevalence and incidence of urinary incontinence in community-dwelling populations. J Am Geriatr Soc. 1990;38:273-81.
Clinical Practice Guideline: Urinary Incontinence in Adults: Acute and Chronic Management. Rockville, Md: US Department of Health and Human Services, Public Health Service; 1996. Agency for Health Care Policy and Research No. 96 - 0682.
Burgio KL, Locher JL, Goode PS, et al. Behavioral vs drug treatment for urge urinary incontinence in elder women: a randomized controlled trial. JAMA. 1998;280:1985-2000.
Fantl JA, Wyman JF, McClish DK, Harkins SW, Elswick RK, Taylor JR. Efficacy of bladder training in older women with urinary incontinence. JAMA. 1991;265:609-13.
Largo-Janssen TL, Debruyne PM, Smits AJ, van Weil C. Controlled trial of pelvic floor exercises in the treatment of urinary stress incontinence in general practice. Br J Gen Pract. 1991;41:445-449.
Subak LL, Quesenberry CP, Posner SF, Cattolica E, Soghikian K. The effect of behavioral therapy on urinary incontinence: a randomized controlled trial. Obstet Gynecol. 2002;100:72-78.
Knott M, Voss DE. Proprioceptive Neuromuscular Facilitation. New York: Harper & Row; 1968.
Hellebrandt FA. Cross education: ipsilateral and contralateral effects of unilateral training. J Appl Physiology. 1951;4:136.
Kannus P, Alosa D, Cook L, et al. Effects of one-legged exercise on strength, power and endurance using isometric and concentric isokinetic training. Eur J Appl Physiol. 1992;64:117-126.
Massey GB. Conservative Gynecology and Electo-Therapeutics. Philadelphia: F.A. Davis Company; 1889.
Brubaker LT, Benson JT, Bent A, Clark A, Shott S. Transvaginal electrical stimulation for female urinary incontinence. Am J Obstet Gynecol. 1997;177:536-540.
Fall M, Lindstrom S. Electrical stimulation: a physiological approach to the treatment of urinary incontinence. Urol Clin North Am. 1991;18:383-407.
Goldthwaite JE. The relation of posture to human efficiency and the influence of poise upon the support and function of the viscera. Boston Medical and Surgical Journal. 1909;161:839-848.
Lind LR, Lucente V, Kohn N. Thoracic kyphosis and the prevalence of advanced uterine prolapse. Obstet Gynecol. 1996;87:605-9.
Penrose CB. Textbook of Diseases of Women. Philadelphia: WB Saunders; 1907.
Sapsford RR, Hodges PW. Contraction of the pelvic floor during abdominal maneuvers. Arch Phys Med Rehabil. 2001;82:1081-88.
Jones DA, Round JM. Skeletal Muscle in Health and Disease. Manchester, England: Manchester University Press; 1990:21.
Exploratory and analytical survey of therapeutic exercise. Northwestern University Special Therapeutic Exercise Project. Am J Phys Med. 1967;46:1-1135.
Unilateral arm strength training improves contralateral peak force and rate of force development Journal European Journal of Applied Physiology
ISSN 1439-6319 (Print) 1439-6327 (Online)Issue Volume 103, Number 5 / July, 2008
Pages 553-559SpringerLink Date Tuesday, April 29, 2008
Michael Adamson1, Niall MacQuaide1, Jan Helgerud2, 3, Jan Hoff2, 4 and Ole Johan Kemi1, 2 (1) Institute of Biomedical and Life Sciences, University of Glasgow, West Medical Building, Glasgow, G12 8QQ, UK
(2) Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway
(3) Hokksund Medical Rehabilitation Center, Hokksund, Norway
(4) Department of Physical Medicine and Rehabilitation, St Olavs Hospital, Trondheim, Norway
Accepted: 16 April 2008 Published online: 29 April 2008
Abstract
Neural adaptation following maximal strength training improves the ability to rapidly develop force. Unilateral strength training also leads to contralateral strength improvement, due to cross-over effects. However, adaptations in the rate of force development and peak force in the contralateral untrained arm after one-arm training have not been determined. Therefore, we aimed to detect contralateral effects of unilateral maximal strength training on rate of force development and peak force. Ten adult females enrolled in a 2-month strength training program focusing of maximal mobilization of force against near-maximal load in one arm, by attempting to move the given load as fast as possible. The other arm remained untrained. The training program did not induce any observable hypertrophy of any arms, as measured by anthropometry. Nevertheless, rate of force development improved in the trained arm during contractions against both submaximal and maximal loads by 40–60%. The untrained arm also improved rate of force development by the same magnitude. Peak force only improved during a maximal isometric contraction by 37% in the trained arm and 35% in the untrained arm. One repetition maximum improved by 79% in the trained arm and 9% in the untrained arm. Therefore, one-arm maximal strength training focusing on maximal mobilization of force increased rapid force development and one repetition maximal strength in the contralateral untrained arm. This suggests an increased central drive that also crosses over to the contralateral side.
Training With Unilateral Resistance Exercise Increases Contralateral Strength
Munn J, Herbert RD, Hancock MJ
J Appl Physiol
vol. 99, 1880 - 1884, 2005
Abstract
Background: A recent meta-analysis of randomized studies found that unilateral training produces a small but statistically significant effect on the strength of the homologous muscles on the contralateral side. However, the studies included in the meta-analysis have several limitations. No consensus exists on the mechanism that produces contralateral strength adaptations, but the magnitude of strength gained on the contralateral side has been suggested to relate to the strength gain on the trained side. The objective of this study was to investigate factors that affect increases in strength of an untrained limb when the contralateral limb is trained.
Methods: Subjects were randomly assigned to a control group of 1 of 4 training groups that performed supervised elbow flexion contractions: 1 set at high speed, 1 set at low speed, 3 sets at high speed, or 3 sets at low speed. Training was conducted 3 times per week for 6 weeks, with a 6- to 8-repetition maximal load. A group of control subjects attended these sessions but did not exercise. Elbow flexor strength was measured with a 1-repetition maximum arm curl before and after training.
Results: Training with 1 set at slow speed did not provide an increase in contralateral strength. However, training with 3 sets increased strength of the untrained arm by a mean of 7% of initial strength. Training with fast contractions tended to produce a greater increase in contralateral strength than that attained with slow training (Table 1). However, the number of sets and training speed did not show any interaction.
Conclusions: Three sets of progressive dynamic resistance exercise produced small contralateral increases in strength, which are graded according to the increases in ipsilateral strength. However, whether this small increase in contralateral strength is functionally important has not been determined.
Original Article
|
Unilateral nerve injury produces bilateral loss of distal innervation
|
|
Anne Louise Oaklander, MD, PhD *, Jennifer M. Brown, BS
|
|
Nerve Injury Unit, Departments of Anesthesiology, Neurology, and Neuropathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA
|
|
|
*Correspondence to Anne Louise Oaklander, Massachusetts General Hospital, 55 Fruit Street, Clinics 3, Boston, MA 02114
Funded by:
NIH, NINDS; Grant Number: R01NS42866
Paul Beeson Scholarship from the American Federation for Aging Research
|
There are no known anatomical connections between neurons that innervate homologous right and left body parts. Nevertheless, some patients develop bilateral abnormalities after unilateral injury, a phenomenon often unrecognized and not yet characterized. Therefore, we examined in rats the effects of ligating and cutting one tibial nerve on sensory |
