Phantom limb pain: relief by application of TENS to contralateral extremity.
Carabelli RA, Kellerman WC. Arch Phys Med Rehabil. 1985 Jul;66(7):466-7.
Three adult patients with below-knee amputation of various etiologies were treated at Norristown's Sacred Heart Hospital and Rehabilitation Center in the fall of 1983. The patients ranged in age from 48 to 64 years and two were men.
All three had complaints of phantom limb pain originating from various anatomic sites of the amputated extremity. In all three cases the phantom limb pain was severe and hampered prosthetic training.
The patients were treated solely by application of the TENS unit to the contralateral extremity at the sites where the phantom pain originated on the amputated limb.
All three patients responded to treatment and were able to continue their prosthetic training. A six-month follow-up showed no pain recurrence of phantom limb pain in all three cases.
Etymology: L, contra, against, latus, side, reflectere, to bend back
an overflow phenomenon of the nervous system in which a reflex is elicited on one side of the body by a stimulus to the opposite side.
Mosby's Medical Dictionary, 8th edition. © 2009, Elsevier.
Contralateral reflex arcs involve sensory receptors and neurons on one side of the body and motor neurons and effectors on the opposite side.
Allen, Connie, and Valerie Harper. Anatomy and Physiology Binder Ready Version. 3rd ed. Danvers: John Wiley & Sons, 2008.
"Under normal conditions, the pupils of both eyes respond identically to a light stimulus, regardless of which eye is being stimulated. Light entering one eye produces a constriction of the pupil of that eye, the direct response, as well as a constriction of the pupil of the unstimulated eye, the consensual response."
Cross education and immobilisation: Mechanisms and implications for injury rehabilitation. J Sci Med Sport. 2012 Mar;15(2):94-101. Epub 2011 Sep 15. Hendy AM, Spittle M, Kidgell DJ.
Unilateral strength training produces an increase in strength of the contralateral homologous muscle group. This process of strength transfer, known as cross education, is generally attributed to neural adaptations. It has been suggested that unilateral strength training of the free limb may assist in maintaining the functional capacity of an immobilised limb via cross education of strength, potentially enhancing recovery outcomes following injury. Therefore, the purpose of this review is to examine the impact of immobilisation, the mechanisms that may contribute to cross education, and possible implications for the application of unilateral training to maintain strength during immobilisation.
Immobilisation is well known for its detrimental effects on muscular function. Early reductions in strength outweigh atrophy, suggesting a neural contribution to strength loss, however direct evidence for the role of the central nervous system in this process is limited. Similarly, the precise neural mechanisms responsible for cross education strength transfer remain somewhat unknown. Two recent studies demonstrated that unilateral training of the free limb successfully maintained strength in the contralateral immobilised limb, although the role of the nervous system in this process was not quantified.
Cross education provides a unique opportunity for enhancing rehabilitation following injury. By gaining an understanding of the neural adaptations occurring during immobilisation and cross education, future research can utilise the application of unilateral training in clinical musculoskeletal injury rehabilitation.
Cross-education of muscle strength: cross-training effects are not confined to untrained contralateral homologous muscle. Scand J Med Sci Sports. 2011 Dec;21(6):e359-64. doi: 10.1111/j.1600-0838.2011.01311.x. Epub 2011 Apr 18.
Sariyildiz M, Karacan I, Rezvani A, Ergin O, Cidem M.
The aim of this study was to evaluate whether electrical muscle stimulation (EMS) on dominant wrist flexors causes an increase in the muscle strength of the contralateral wrist extensors. Twenty-three healthy, young, adult men were included in this prospective, double-blind, controlled study. Participants were randomly allocated to the EMS group or Control group. Electrodes were placed over the flexor aspect of the right forearm in both groups. In the EMS group, passive wrist extension and (EMS) that caused powerful muscle contraction were simultaneously applied. In the Control group, a conventional mode of transcutaneous electrical nerve stimulation was applied without causing any contraction. A group effect (P=0.0001) and group-by-time interaction were found (P=0.0001) for both the wrist flexor and extensor muscles, but not group-by-time-by-arm interactions. This implies that the effect of the interventions was similar in both arms, but that the response was significantly larger in the EMS than in the Control group. The results of the current study suggest that cross-education is not confined to the untrained contralateral wrist flexors and that the strength increase may also be observed in the contralateral wrist extensors.
Neuro-physiological adaptations associated with cross-education of strength.
Farthing JP, Borowsky R, Chilibeck PD, Binsted G, Sarty GE.
Brain Topogr. 2007 Winter;20(2):77-88. Epub 2007 Oct 12.
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.
Strength gains by motor imagery with different ratios of physical to mental practice. Reiser M, Büsch D, Munzert J. Front Psychol. 2011;2:194. Epub 2011 Aug 19.
The purpose of this training study was to determine the magnitude of strength gains following a high-intensity resistance training (i.e., improvement of neuromuscular coordination) that can be achieved by imagery of the respective muscle contraction imagined maximal isometric contraction (IMC training). Prior to the experimental intervention, subjects completed a 4-week standardized strength training program. 3 groups with different combinations of real maximum voluntary contraction (MVC) and mental (IMC) strength training (M75, M50, M25; numbers indicate percentages of mental trials) were compared to a MVC-only training group (M0) and a control condition without strength training (CO). Training sessions (altogether 12) consisted of four sets of two maximal 5-s isometric contractions with 10 s rest between sets of either MVC or IMC training. Task-specific effects of IMC training were tested in four strength exercises commonly used in practical settings (bench pressing, leg pressing, triceps extension, and calf raising). Maximum isometric voluntary contraction force (MVC) was measured before and after the experimental training intervention and again 1 week after cessation of the program. IMC groups (M25, M50, M75) showed slightly smaller increases in MVC (3.0% to 4.2%) than M0 (5.1%), but significantly stronger improvements than CO (-0.2%). Compared to further strength gains in M0 after 1 week (9.4% altogether), IMC groups showed no "delayed" improvement, but the attained training effects remained stable. It is concluded that high-intensity strength training sessions can be partly replaced by IMC training sessions without any considerable reduction of strength gains.
Benefits of motor imagery training on muscle strength.
Lebon F, Collet C, Guillot A. J Strength Cond Res. 2010 Jun;24(6):1680-7.
It is well established that motor imagery (MI) improves motor performance and motor learning efficiently. Previous studies provided evidence that muscle strength may benefit from MI training, mainly when movements are under the control of large cortical areas in the primary motor cortex. The purpose of this experiment is to assess whether MI might improve upper and lower limbs' strength through an ecological approach and validation, with complex and multijoint exercises. Nine participants were included in the MI group and 10 in the control (CTRL) group. The 2 groups performed identical bench press and leg press exercises. The MI group was instructed to visualize and feel the correspondent contractions during the rest period, whereas the CTRL group carried out a neutral task. The maximal voluntary contraction (MVC) and the maximal number of repetitions (MR) using 80% of the pre-test MVC weight were measured. Although both MI and CTRL groups enhanced their strength through the training sessions, the leg press MVC was significantly higher in the MI group than in the CTRL group (p<0.05). The interaction between the leg press MR and the group was marginally significant (p=0.076). However, we did not find any difference between the MI and CTRL groups, both in the bench press MVC and MR. MI-related training may contribute to the improvement of lower limbs performance by enhancing the technical execution of the movement, and the individual intrinsic motivation. From an applied and practical perspective, we state that athletes may perform imagined muscles contractions, most especially during the rest periods of their physical training, to contribute to the enhancement of concentric strength.
The ipsilateral motor cortex contributes to cross-limb transfer of performance gains after ballistic motor practice. Lee M, Hinder MR, Gandevia SC, Carroll TJ. J Physiol. 2010 Jan 1;588(Pt 1):201-12. Epub 2009 Nov 16
Although it has long been known that practicing a motor task with one limb can improve performance with the limb opposite, the mechanisms remain poorly understood. Here we tested the hypothesis that improved performance with the untrained limb on a fastest possible (i.e. ballistic) movement task depends partly on cortical circuits located ipsilateral to the trained limb. The idea that crossed effects, which are important for the learning process, might occur in the 'untrained' hemisphere following ballistic training is based on the observation that tasks requiring strong descending drive generate extensive bilateral cortical activity. Twenty-one volunteers practiced a ballistic index finger abduction task with their right hand, and corticospinal excitability was assessed in two hand muscles (first dorsal interosseus, FDI; adductor digiti minimi, ADM). Eight control subjects did not train. After training, repetitive transcranial magnetic stimulation (rTMS; 15 min at 1 Hz) was applied to the left (trained) or right (untrained) motor cortex to induce a 'virtual lesion'. A third training group received sham rTMS, and control subjects received rTMS to the right motor cortex. Performance and corticospinal excitability (for FDI) increased in both hands for training but not control subjects. rTMS of the left, trained motor cortex specifically reduced training-induced gains in motor performance for the right, trained hand, and rTMS of the right, untrained motor cortex specifically reduced performance gains for the left, untrained hand. Thus, cortical processes within the untrained hemisphere, ipsilateral to the trained hand, contribute to early retention of ballistic performance gains for the untrained limb.
Effects of cross-education on the muscle after a period of unilateral limb immobilization using a shoulder sling and swathe. Magnus CR, Barss TS, Lanovaz JL, Farthing JP.
J Appl Physiol. 2010 Dec;109(6):1887-94. Epub 2010 Oct 21.
The purpose of this study was to apply cross-education during 4 wk of unilateral limb immobilization using a shoulder sling and swathe to investigate the effects on muscle strength, muscle size, and muscle activation. Twenty-five right-handed participants were assigned to one of three groups as follows: the Immob + Train group wore a sling and swathe and strength trained (n = 8), the Immob group wore a sling and swathe and did not strength train (n = 8), and the Control group received no treatment (n = 9). Immobilization was applied to the nondominant (left) arm. Strength training consisted of maximal isometric elbow flexion and extension of the dominant (right) arm 3 days/wk. Torque (dynamometer), muscle thickness (ultrasound), maximal voluntary activation (interpolated twitch), and electromyography (EMG) were measured. The change in right biceps and triceps brachii muscle thickness [7.0 ± 1.9 and 7.1 ± 2.2% (SE), respectively] was greater for Immob + Train than Immob (0.4 ± 1.2 and -1.9 ± 1.7%) and Control (0.8 ± 0.5 and 0.0 ± 1.1%, P < 0.05). Left biceps and triceps brachii muscle thickness for Immob + Train (2.2 ± 0.7 and 3.4 ± 2.1%, respectively) was significantly different from Immob (-2.8 ± 1.1 and -5.2 ± 2.7%, respectively, P < 0.05). Right elbow flexion strength for Immob + Train (18.9 ± 5.5%) was significantly different from Immob (-1.6 ± 4.0%, P < 0.05). Right and left elbow extension strength for Immob + Train (68.1 ± 25.9 and 32.2 ± 9.0%, respectively) was significantly different from the respective limb of Immob (1.3 ± 7.7 and -6.1 ± 7.8%) and Control (4.7 ± 4.7 and -0.2 ± 4.5%, P < 0.05). Immobilization in a sling and swathe decreased strength and muscle size but had no effect on maximal voluntary activation or EMG. The cross-education effect on the immobilized limb was greater after elbow extension training. This study suggests that strength training the nonimmobilized limb benefits the immobilized limb for muscle size and strength.
Corticospinal adaptations and strength maintenance in the immobilized arm following 3 weeks unilateral strength training. Pearce AJ, Hendy A, Bowen WA, Kidgell DJ. Scand J Med Sci Sports. 2012 Mar 19. doi: 10.1111/j.1600-0838.2012.01453.x. [Epub ahead of print]
Cross-education strength training has being shown to retain strength and muscle thickness in the immobilized contralateral limb. Corticospinal mechanisms have been proposed to underpin this phenomenon; however, no transcranial magnetic stimulation (TMS) data has yet been presented. This study used TMS to measure corticospinal responses following 3 weeks of unilateral arm training on the contralateral, immobilize arm. Participants (n = 28) were randomly divided into either immobilized strength training (Immob + train) immobilized no training (Immob) or control. Participants in the immobilized groups had their nondominant arm rested in a sling, 15 h/day for 3 weeks. The Immob + train group completed unilateral arm curl strength training, while the Immob and control groups did not undertake training. All participants were tested for corticospinal excitability, strength, and muscle thickness of both arms. Immobilization resulted in a group x time significant reduction in strength, muscle thickness and corticospinal excitability for the untrained limb of the Immob group. Conversely, no significant change in strength, muscle thickness, or corticospinal excitability occurred in the untrained limb of the Immob + train group. These results provide the first evidence of corticospinal mechanisms, assessed by TMS, underpinning the use of unilateral strength training to retain strength and muscle thickness following immobilization of the contralateral limb.
Changes in functional magnetic resonance imaging cortical activation with cross education to an immobilized limb. Farthing JP, Krentz JR, Magnus CR, Barss TS, Lanovaz JL, Cummine J, Esopenko C, Sarty GE, Borowsky R. Med Sci Sports Exerc. 2011 Aug;43(8):1394-405.
The purpose of this study was to assess cortical activation associated with the cross-education effect to an immobilized limb, using functional magnetic resonance imaging.
Fourteen right-handed participants were assigned to two groups. One group (n = 7) wore a cast and strength trained the free arm (CAST-TRAIN). The second group (n = 7) wore a cast and did not strength train (CAST). Casts were applied to the nondominant (left) wrist and hand. Strength training was maximal isometric handgrip contractions (right hand) 5 d·wk(-1). Peak force (handgrip dynamometer), muscle thickness (ultrasound), EMG, and cortical activation (functional magnetic resonance imaging) were assessed before and after the intervention.
CAST-TRAIN improved right handgrip strength by 10.7% (P < 0.01) with no change in muscle thickness. There was a significant group × time interaction for strength of the immobilized arm (P < 0.05). Handgrip strength of the immobilized arm of CAST-TRAIN was maintained, whereas the immobilized arm of CAST significantly decreased by 11% (P < 0.05). Muscle thickness of the immobilized arm decreased by an average of 3.3% (P < 0.05) for all participants and was not different between groups after adjusting for baseline differences. There was a significant group × time interaction for EMG activation (P < 0.05), where CAST-TRAIN showed an increasing trend and CAST showed a decreasing trend, pooled across arms. For the immobilized arm of CAST-TRAIN, there was a significant increase in contralateral motor cortex activation after training (P < 0.05). For the immobilized arm of CAST, there was no change in motor cortex activation.
Handgrip strength training of the free limb attenuated strength loss during unilateral immobilization. The maintenance of strength in the immobilized limb via the cross-education effect may be associated with increased motor cortex activation.
The effect of contralateral training: Influence of unilateral isokinetic exercise on one-legged standing balance of the contralateral lower extremity in adults. Gait Posture. 2011 May;34(1):103-6. Epub 2011 May 4. Kim K, Cha YJ, Fell DW
To investigate the effects of unilateral isokinetic exercises on the one-legged standing balance of the contralateral lower extremity.
A volunteer sample of 32 healthy adults (12 men and 20 women) was randomized to training and control groups.
The training group received unilateral hip isokinetic exercises of the dominant leg for two weeks. Contralateral single-limb balance was measured before and after intervention, including three stability index scores of balance using Biodex Stability System: Anterior-Posterior Stability Index (APSI), Medio-lateral Stability Index (MLSI), and Overall Stability Index (OSI) scores.
Comparison of pre-test and post-test data revealed significant improvements in APSI, MLSI, and OSI scores in the training group (p<0.05), but not in the control group. The gains of stability scores from pre- to post-test, were also significantly greater (p<0.05) in the training group than the control group.
These results suggest that contralateral training with unilateral isokinetic exercises increases the one-legged standing balance of the contralateral limb following a short duration of training.
Unilateral strength training increases voluntary activation of the opposite untrained limb.
Lee M, Gandevia SC, Carroll TJ. Clin Neurophysiol. 2009 Apr;120(4):802-8. Epub 2009 Feb 18
We investigated whether an increase in neural drive from the motor cortex contributes to the cross-limb transfer of strength that can occur after unilateral strength training.
Twitch interpolation was performed with transcranial magnetic stimulation to assess changes in strength and cortical voluntary activation in the untrained left wrist, before and after 4 weeks of unilateral strength-training involving maximal voluntary isometric wrist extension contractions (MVCs) for the right wrist (n=10, control group=10).
Wrist extension MVC force increased in both the trained (31.5+/-18%, mean+/-SD, p<0.001) and untrained wrist (8.2+/-9.7%, p=0.02), whereas wrist abduction MVC did not change significantly. The amplitude of the superimposed twitches evoked during extension MVCs decreased by 35% (+/-20%, p<0.01), which contributed to a significant increase in voluntary activation (2.9+/-3.5%, p<0.01). Electromyographic responses to cortical and peripheral stimulation were unchanged by training. There were no significant changes for the control group which did not train.
Unilateral strength training increased the capacity of the motor cortex to drive the homologous untrained muscles.
The data show for the first time that an increase in cortical drive contributes to the contralateral strength training effect.
Tenocyte hypercellularity and vascular proliferation in a rabbit model of tendinopathy: contralateral effects suggest the involvement of central neuronal mechanisms
Br J Sports Med 2011;45:399-406 doi:10.1136/bjsm.2009.068122
Gustav Andersson, Sture Forsgren, Alexander Scott, James Edmund, Gaida, Johanna Elgestad Stjernfeldt, Ronny Lorentzon, Håkan Alfredson, Clas Backman, Patrik Danielson
To determine whether there are objective findings of tendinosis in a rabbit tendinopathy model on exercised and contralateral (non-exercised) Achilles tendons.
Four groups of six New Zealand white rabbits per group were used. The animals of one (control) group were not subjected to exercise/stimulation
Animals were subjected to a protocol of electrical stimulation and passive flexion–extension of the right triceps surae muscle every second day for 1, 3 or 6 weeks.
Main Outcome Measures:
Tenocyte number and vascular density were calculated. Morphological evaluations were also performed as well as in-situ hybridisation for vascular endothelial growth factor (VEGF) messenger RNA.
There was a significant increase in the tenocyte number after 3 and 6 weeks of exercise, but not after 1 week, in comparison with the control group. This was seen in the Achilles tendons of both legs in experimental animals, including the unexercised limb. The pattern of vascularity showed an increase in the number of tendon blood vessels in rabbits that had exercised for 3 weeks or more, compared with those who had exercised for 1 week or not at all. VEGF-mRNA was detected in the investigated tissue, with the reactions being more clearly detected in the tendon tissue with tendinosis-like changes (6-week rabbits) than in the normal tendon tissue (control rabbits).
There were bilateral tendinosis-like changes in the Achilles tendons of rabbits in the current model after 3 weeks of training, suggesting that central neuronal mechanisms may be involved and that the contralateral side is not appropriate as a control.
Training with unilateral resistance exercise increases contralateral strength
Joanne Munn, Robert D. Herbert, Mark J. Hancock, and Simon C. Gandevia
Journal of Applied Physiology November 2005 vol. 99 no. 5 1880-1884
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.
Electromyography Results of Exercise Overflow in Hemiplegic Patients
Virginia M Mills and Lee Quintana Physical Therapy July 1985 vol. 65 no. 7 1041-1045
The purpose of this study was to determine the effects of exercise overflow in hemiplegic patients. Eleven subjects with a diagnosis of cerebrovascular accident (CVA) performed active exercises with their uninvolved extremities while their involved extremities were monitored with EMG. The muscles monitored were the biceps brachii, triceps brachii, and quadriceps femoris. Active exercise of the comparable uninvolved muscles was performed under three different weight lifting conditions: 1) maximal weight, 2) 50% of the maximal weight, and 3) no weight. Significant (p < .05) overflow to the involved nonexercised extremities was found in all of the exercise conditions. Overflow was frequently found in all three muscle groups when only one muscle group was being exercised. Overflow always occurred in the contralateral homologous muscle. Exercise overflow appears to be an effective therapeutic technique to facilitate muscle activity in paretic muscles. This muscle activity may cause desired or undesired muscular effects during therapy in the rehabilitation of patients with CVAs.
Cross-Education After One Session of Unilateral Surface Electrical Stimulation of the Rectus Femoris, Toca-Herrera, José L; Gallach, José E; Gómis, Manuel; González, Luis M, Journal of Strength & Conditioning Research:
March 2008 - Volume 22 - Issue 2 - pp 614-618
Thirty-six adult men were randomly assigned to a remote stimulation group (RS; n = 18) or control group (CTL; n = 18). The RS group unilaterally performed a 10-minute surface electrical stimulation program (frequency 100 Hz, impulse 300 μs, 10 seconds on/10 seconds off) on the rectus femoris of the non-dominant leg. The subjects of the CTL group relaxed for 10 minutes without performing any training. Immediately before and after the surface electrical stimulation program, the isometric strength and the electromyographic (EMG) and mechanomyographic (MMG) response of the dominant leg was measured for all subjects. The dominant leg of the RS group showed a significant increase in the isometric force (5.11%; P < 0.001) and EMG activity of the agonist muscle (4.67%; P < 0.05), whereas a decrease in EMG activity of the antagonist muscles was observed (-10.27%; P < 0.05). The MMG activity did not show any alteration. No significant changes were observed for the CTL group. These results indicate that one unilateral surface electrical stimulation session on the rectus femoris improves the efficiency of the inactive leg. At a practical level, the results open a new way to rehabilitate muscle-skeletal injuries, especially weak members that cannot do any physical work. In this case, the muscle strength (and physical efficiency) can be improved by passive electrostimulation training on the healthy member.
Effects of unilateral electromyostimulation superimposed on voluntary training on strength and cross-sectional area, Pedro Bezerra MSc, Shi Zhou PhD, Zachary Crowley BSc, Lyndon Brooks PhD, Andrew Hooper MD; Muscle & Nerve Volume 40, Issue 3, pages 430–437, September 2009
In this study we investigate the effects of unilateral voluntary contraction (VC) and electromyostimulation superimposed on VC (EV) training on maximal voluntary (MVC) force and cross-sectional area (CSA), as assessed by magnetic resonance imaging of knee extensors. Thirty young men were randomly assigned to either a control group (CG), VC group (VG), or EV group (EVG). The VG and EVG trained the right leg isometrically three sessions per week for 6 weeks. After training, MVC increased in the right leg in the VG and in both legs in the EVG, and EVG was significantly different from CG (all P < 0.01). Increased CSA was found only in the right leg in the VG and EVG (P < 0.01), and correlated with improvements of MVC (r = 0.49, P = 0.01). It appeared that the EV training was equally effective as VC at increasing MVC and CSA, while having a greater cross-education effect. Increased strength without muscle hypertrophy in the unexercised leg of the EVG indicated that neural adaptation was responsible for the cross-education effect. Muscle Nerve 40: 430–437, 2009