Cross-education Effect Research Articles

Cross-education does not accelerate the rehabilitation of neuromuscular functions after ACL reconstruction: a randomized controlled clinical trial

PurposeCross-education reduces quadriceps weakness 8 weeks after anterior cruciate ligament (ACL) surgery, but the long-term effects are unknown. We investigated whether cross-education, as an adjuvant to the standard rehabilitation, would accelerate recovery of quadriceps strength and neuromuscular function up to 26 weeks post-surgery.MethodsGroup allocation was randomized. The experimental (n = 22) and control (n = 21) group received standard rehabilitation. In addition, the experimental group strength trained the quadriceps of the non-injured leg in weeks 1–12 post-surgery (i.e., cross-education). Primary and secondary outcomes were measured in both legs 29 ± 23 days prior to surgery and at 5, 12, and 26 weeks post-surgery.ResultsThe primary outcome showed time and cross-education effects. Maximal quadriceps strength in the reconstructed leg decreased 35% and 12% at, respectively, 5 and 12 weeks post-surgery and improved 11% at 26 weeks post-surgery, where strength of the non-injured leg showed a gradual increase post-surgery up to 14% (all p ≤ 0.015). Limb symmetry deteriorated 9–10% more for the experimental than control group at 5 and 12 weeks post-surgery (both p ≤ 0.030). One of 34 secondary outcomes revealed a cross-education effect: Voluntary quadriceps activation of the reconstructed leg was 6% reduced for the experimental vs. control group at 12 weeks post-surgery (p = 0.023). Both legs improved force control (22–34%) and dynamic balance (6–7%) at 26 weeks post-surgery (all p ≤ 0.043). Knee joint proprioception and static balance remained unchanged.ConclusionStandard rehabilitation improved maximal quadriceps strength, force control, and dynamic balance in both legs relative to pre-surgery but adding cross-education did not accelerate recovery following ACL reconstruction.

UNILATERAL AND BILATERAL EXERCISE MOVEMENTS

Apply It! By reading this article, the health and fitness professional will: Understand neurophysiological concepts such as the bilateral deficit, bilateral facilitation, and cross-education effect and extend their potential applications to exercise prescription Prescribe bilateral and unilateral exercises for the appropriate clientele based on an evidence-based rationale

Contralateral effects of unilateral training: sparing of muscle strength and size after immobilization.

The contralateral effects of unilateral strength training, known as cross-education of strength, date back well over a century. In the last decade, a limited number of studies have emerged demonstrating the preservation or "sparing" effects of cross-education during immobilization. Recently published evidence reveals that the sparing effects of cross-education show muscle site specificity and involve preservation of muscle cross-sectional area. The new research also demonstrates utility of training with eccentric contractions as a potent stimulus to preserve immobilized limb strength across multiple modes of contraction. The cumulative data in nonclinical settings suggest that cross-education can completely abolish expected declines in strength and muscle size in the range of ∼13% and ∼4%, respectively, after 3-4 weeks of immobilization of a healthy arm. The evidence hints towards the possibility that unique mechanisms may be involved in preservation effects of cross-education, as compared with those that lead to functional improvements under normal conditions. Cross-education effects after strength training appear to be larger in clinical settings, but there is still only 1 randomized clinical trial demonstrating the potential utility of cross-education in addition to standard treatment. More work is necessary in both controlled and clinical settings to understand the potential interaction of neural and muscle adaptations involved in the observed sparing effects, but there is growing evidence to advocate for the clinical utility of cross-education.

Evidence of homologous and heterologous effects after unilateral leg training in youth.

The positive effects of unilateral training on contralateral muscles (cross education) has been demonstrated with adults for over a century. There is limited evidence for cross education of heterologous muscles. Cross education has not been demonstrated with children. It was the objective of this study to investigate cross-education training in children examining ipsilateral and contralateral homologous and heterologous muscles. Forty-eight male children (aged 10-13 years) were assessed for unilateral, ipsilateral and contralateral lower limb strength, power and endurance (1-repetition maximum (RM) leg press, knee extensors (KE) and flexors (KF) maximum voluntary isometric contractions (MVIC), countermovement jump, muscle endurance test (leg press repetitions with 60% 1RM)), and upper body unilateral MVIC elbow flexors (EF) and handgrip strength. An 8-week training program involved 2 unilateral leg press resistance-training groups (high load/low repetitions: 4-8 sets of 5RM, and low load/high repetitions: 1-2 sets of 20RM) and control (untrained) group. All muscles exhibited improvements of 6.1% to 89.1%. The trained limb exhibited greater adaptations than the untrained limb for leg press 1RM (40.3% vs. 25.2%; p = 0.005), and 60% 1RM leg press (104.1% vs. 73.4%; p = 0.0001). The high load/low repetition training induced (p < 0.0001) greater improvements than low load/high repetition with KE, KF, EF MVIC and leg press 1RM. This is the first study to demonstrate cross-education effects with children and that the effects of unilateral training involve both contralateral homologous and heterologous muscles with the greatest strength-training responses from high-load/low-repetition training.

The Cross-Education Phenomenon: Brain and Beyond.

Objectives: Unilateral resistance training produces strength gains in the untrained homologous muscle group, an effect termed “cross-education.” The observed strength transfer has traditionally been considered a phenomenon of the nervous system, with few studies examining the contribution of factors beyond the brain and spinal cord. In this hypothesis and theory article, we aim to discuss further evidence for structural and functional adaptations occurring within the nervous, muscle, and endocrine systems in response to unilateral resistance training. The limitations of existing cross-education studies will be explored, and novel potential stakeholders that may contribute to the cross-education effect will be identified.Design: Critical review of the literature.Method: Search of online databases.Results: Studies have provided evidence that functional reorganization of the motor cortex facilitates, at least in part, the effects of cross-education. Cross-activation of the “untrained” motor cortex, ipsilateral to the trained limb, plays an important role. While many studies report little or no gains in muscle mass in the untrained limb, most experimental designs have not allowed for sensitive or comprehensive investigation of structural changes in the muscle.Conclusions: Increased neural drive originating from the “untrained” motor cortex contributes to the cross-education effect. Adaptive changes within the muscle fiber, as well as systemic and hormonal factors require further investigation. An increased understanding of the physiological mechanisms contributing to cross-education will enable to more effectively explore its effects and potential applications in rehabilitation of unilateral movement disorders or injury.

Cross‐education after high‐frequency versus low‐frequency volume‐matched handgrip training

Cross-education training programs cause interlimb asymmetry of strength and hypertrophy. We examined the cross-education effects from a high-frequency (HF) versus a low-frequency (LF) volume-matched handgrip training program on interlimb asymmetry. Right-handed participants completed either HF (n = 10; 2 × 6 repetitions 10 times per week) or LF (n = 9; 5 × 8 repetitions 3 times per week) training. Testing occurred twice before and once after 4 weeks of right-handed isometric handgrip training totaling 120 weekly repetitions. Measures were maximal isometric handgrip and wrist flexion torque, muscle thickness, and muscle activation (electromyography; EMG). Grip strength was greater in both limbs posttraining, pooled across groups (P < 0.001). Trained limb muscle thickness increased in both groups (P < 0.05; untrained, P = 0.897). EMG and wrist flexion torque did not change (all P > 0.103). Both LF and HF induced cross-education of grip strength to the untrained limb, but HF did not reduce asymmetry. These findings have implications for injury rehabilitation. Muscle Nerve 56: 689-695, 2017.

Can Handgrip Strength Improve Following Body Mass-Based Lower Body Exercise?

Knee extension strength (KES) improves following body mass-based lower body exercise training; however, it is unknown whether this type of exercise increases handgrip strength (HGS) as a result of a cross-education effect in older individuals. Our aim was to investigate the effect of a body mass-based exercise intervention on HGS and KES in older adults. At baseline, 166 subjects started a 12-week intervention program, and 160 (108 women and 52 men) subjects completed the study. A self-selected group of 37 older adults (21 women and 16 men) served as a control group. HGS, KES, and ultrasound-derived anterior thigh muscle thickness (anterior thigh MT) were measured at baseline and post-testing, and relative strength of the knee extensor (KES/anterior thigh MT) was calculated. A linear regression model controlling for baseline values of body–mass index, % body fat, fat-free mass, HGS, chair stand time, anterior thigh MT, and KES/body mass ratio found a significant difference between control and training groups for KES post-testing values (p = 0.001) and anterior thigh MT post-testing values (p = 0.012), but not for HGS post-testing values (p = 0.287). Our results suggest that increases in lower body strength and muscle size following a 12-week lower body mass-based exercise intervention fail to translate into improvements in HGS.

No evidence of neural adaptations following chronic unilateral isometric training of the intrinsic muscles of the hand: a randomized controlled study.

To test whether long-term cortical adaptations occur bilaterally following chronic unilateral training with a simple motor task. Participants (n=34) were randomly allocated to a training or control groups. Only the former completed a 4-week maximal-intensity isometric training of the right first dorsal interosseus muscle through key pinching. Maximal strength was assessed bilaterally in four different movements progressively less similar to the training task: key, tip and tripod pinches, and handgrip. Transcranial magnetic stimulation was used to probe, in the left and right primary hand motor cortices, a number of standard tests of cortical excitability, including thresholds, intra-cortical inhibition and facilitation, transcallosal inhibition, and sensory-motor integration. Training increased strength in the trained hand, but only for the tasks specifically involving the trained muscle (key +8.5%; p<0.0005; tip +7.2%; p=0.02). However, the effect size was small and below the cutoff for meaningful change. Handgrip and tripod pinch were instead unaffected. There was a similar improvement in strength in the untrained hand, i.e., a cross-education effect (key +6.4%; p=0.02; tip +4.7%; p=0.007). Despite these changes in strength, no significant variation was observed in any of the neurophysiological parameters describing cortico-spinal and intra-cortical excitability, inter-hemispheric inhibition, and cortical sensory-motor integration. A 4-week maximal-intensity unilateral training induced bilaterally spatial- and task-specific strength gains, which were not associated to direct or crossed cortical adaptations. The observed long-term stability of neurophysiological parameters might result from homeostatic plasticity phenomena, aimed at restoring the physiological inter-hemispheric balance of neural activity levels perturbed by the exercise. ClinicalTrials.gov identifier NCT02010398.

Mirror Training Augments the Cross-education of Strength and Affects Inhibitory Paths.

Unilateral strength training strengthens not only the muscles on the trained side but also the homologous muscles on the untrained side; however, the magnitude of this interlimb cross-education is modest. We tested the hypothesis that heightened sensory feedback by mirror viewing the exercising hand would augment cross education by modulating neuronal excitability. Healthy adults were randomized into a mirror training group (MG, N = 11) and a no-mirror training group (NMG, N = 12) and performed 640 shortening muscle contractions of the right wrist flexors at 80% maximum voluntary contraction (MVC) during 15 sessions for 3 wk. Maximal strength and specific transcranial magnetic stimulation metrics of neuronal excitability, measured in the mirror and no-mirror setup at rest and during unilateral contractions at 60% MVC, were assessed before and after the strength intervention. Trained wrist flexor MVC increased 72% across groups, whereas cross-education was higher for the MG (61%) than NMG (34%, P = 0.047). The MG showed a reduction (15%-16%) in the contralateral silent period duration measured from the contracting left-untrained flexor carpi radialis, whereas the NMG showed an increase (12%, P ≤ 0.030). Interhemispheric inhibition, measured from the trained to the untrained primary motor cortex, increased in the MG (11%) but decreased in the NMG (15%) when measured in the mirror setup at rest (P = 0.048). Other transcranial magnetic stimulation measures did not change. Viewing the exercising hand in a mirror can augment the cross-education effect. The use of a mirror in future studies can potentially accelerate functional recovery from unilateral impairment due to stroke or upper limb fracture.

Cross-education Effects After High Versus Low Frequency, Volume-matched Grip Strength Training.

Unilateral strength training can attenuate muscle mass and strength losses in an opposite immobilized limb. Traditional unilateral training programs that yield these cross-education effects cause inter-limb asymmetry by inducing hypertrophy and strength increases in the trained limb. A higher frequency training program with lower per session volume may attenuate trained limb hypertrophy but still yield cross-education effects, lowering inter-limb asymmetry. PURPOSE: To determine the effects of a high frequency (HF) vs. low frequency (LF) volume-matched 4-week isometric grip strength training program on cross-education of strength. METHODS: Nineteen healthy right-handed participants (age 24±5 years) were randomly assigned to one of two groups: HF (n=10) and LF (n=9). Participants were tested twice before and once after a 4-week, unilateral (right) grip strength training program totaling 120 maximal repetitions per week. HF trained twice per day, 5 days per week, 2 sets of 6 repetitions per session. LF trained 3 days per week, 5 sets of 8 repetitions per session. Measures included maximal isometric grip strength (grip dynamometer) and wrist flexion (NORM dynamometer), muscle thickness (ultrasound), muscle activation (EMG) and voluntary activation (twitch-interpolation). RESULTS: A significant time main effect (p<0.001) was observed for isometric grip strength where both limbs increased from pre to post with no differences between groups (LF right: 42.4±12.2 to 46.6±11.1 kg; LF left: 38.6±10.5 to 42.0±10.4 kg; HF right: 47.6±13.6 to 50.5±13.5 kg; HF left: 43.9±11.9 to 47.6±13.3 kg). Muscle thickness significantly increased in both groups in the right limb only (R: 3.93±0.44 to 4.04±0.45 cm, p<0.05; L: 3.88±0.51 to 3.88±0.49 cm, p=0.897). EMG burst activity (normalized to the maximal M wave), maximal isometric wrist flexion torque, and voluntary activation of the forearm muscles did not change significantly from pre to post training in either arm (p=0.256 to 0.831). CONCLUSION: As predicted, both LF and HF training programs were effective for inducing cross-education of grip strength to the untrained limb; however, contrary to our hypothesis, both programs induced similar hypertrophy in the trained limb. These findings have implications for rehabilitation strategies after unilateral injury.

Changes of One-Leg Standing Balance of Ipsilateral and Contralateral Lower-Limb Following Unilateral Isokinetic Exercise of Ankle Joint in Young Adults

Purpose: The purpose of this study was to investigate the effects of a four week unilateral isokinetic exercise program applied to ankle on the one-leg stance balance performance of ipsilateral and contralateral lower-limbs. Methods: Subjects were randomly assigned to either a right ankle training program (n=12) or a control group (n=12). The training group received unilateral ankle isokinetic exercise of the dominant side for 4 weeks, whereas control group did not. Ipsilateral and con tralateral one-leg balance were measured before and after intervention using the Biodex Balance System. Results: Improvements of stability scores, such as APSI, MLSI, and OSI, from pre-test to post-test were significantly different greater for the training group when the control. Conclusion: The results of this study suggest unilateral ankle strengthening exercise transfers benefit to the untrained limb by a cross-education effect, and that this type of exercise should be considered to improve one-leg standing balance of trained and untrained low er-limbs.

Cross-education effect after unilateral eccentric-only isokinetic vs dynamic constant external resistance training

The aim of this study was to evaluate the effects of unilateral eccentric training using constant velocity or constant external load on untrained limb. Forty-nine participants were randomized in isokinetic (IK), dynamic constant external resistance (DCER) unilateral eccentric training or control groups. Knee-extension 1RM and isometric, eccentric and concentric knee extensors’ peak torques, as well as changes in vastus lateralis muscle thickness, fascicle length, pennation angle and quadriceps fat-free mass were measured. After training, both IK and DCER similarly increased over time 1RM (respectively, +3.6 kg, CI 95 % 0.6–6.5 and +4.3 kg, CI 95 % 1.6–6.9), concentric (respectively, +8.4 N/m, CI 95 % 0.0 to +16.4 and 9.8 CI 95 % 0.6–19.2), eccentric (respectively, +28.5 N/m, CI 95 % 11.0 to +46.0 and 21.1 CI 95 % 15.1–37.0), and isometric (respectively, +15.4 N/m, CI 95 % 0.7–30.0 and +13.9, CI 95 % 0.3–27.5) peak torques. No increase was found for vastus lateralis muscle thickness, fascicle length, pennation angle and quadriceps fat-free mass. Eccentric training was effective for inducing strength, but not structural, adaptations in untrained limb. Both in rehabilitation and training practice, use of easily available gym devices can be a good substitute for expensive and often unavailable isokinetic devices.

Anodal Transcranial Direct Current Stimulation Prolongs the Cross-education of Strength and Corticomotor Plasticity.

This study aimed to assess the efficacy of applying anodal transcranial direct-current stimulation (a-tDCS) to the ipsilateral motor cortex (iM1) during unilateral strength training to enhance the neurophysiological and functional effects of cross-education. Twenty-four healthy volunteers were randomly allocated to perform either of the following: strength training during a-tDCS (ST + a-tDCS), strength training during sham tDCS (ST + sham), or a-tDCS during rest (a-tDCS) across 2 wk. Strength training of the right biceps brachii involved four sets of six repetitions at 80% of one-repetition maximum three times per week. Anodal tDCS was applied to the iM1 at 1.5 mA for 15 min during each strength training session. Outcome measures included one-repetition maximum strength of the untrained biceps brachii, corticomotoneuronal excitability, cross-activation, and short-interval intracortical inhibition (SICI) of the iM1 determined by transcranial magnetic stimulation. Immediately after the final training session, there was an increase in strength for both the ST + a-tDCS (12.5%, P < 0.001) and the ST + sham group (9.4%, P = 0.007), which was accompanied by significant increases in corticomotoneuronal excitability and decreases in SICI for both groups. After a 48-h retention period, strength increase was maintained in the ST + a-tDCS (13.0%, P = 0.001) group, which was significantly greater than the ST + sham group (7.6%, P = 0.039). Similarly, increases in corticomotoneuronal excitability and decreases in SICI were maintained in the ST + a-tDCS group but not in the ST + sham group. No main effects were reported for the a-tDCS group (all P > 0.05). The addition of a-tDCS to the iM1 during unilateral strength training prolongs the benefits of cross-education, which may have significant implications to enhancement of rehabilitation outcomes after a single-limb injury or impairment.

Unilateral balance training enhances neuromuscular reactions to perturbations in the trained and contralateral limb

The aim of this study was to investigate the effect of unilateral balance training on the reactive recovery of balance for both trained and untrained limbs. Twenty-three subjects were randomly assigned to either a control group (CG) or a training group (TG). The latter performed six weeks of balance training for the right leg. The pre- and post-training measurements were based on single leg standing posture on a moveable force platform which moved 6cm anteriorly. TG subjects were tested on the trained (TR) and untrained leg (UTR), whereas CG subjects were tested on the right leg (CTR). The center of pressure trajectory length (CPLEN) and average speed (CPSPD) as well as onsets of muscular activation and time to peak (EMGTP) from lower limb muscles were calculated and compared by a 2-way ANOVA (three legs×two training status). Muscular onsets were reduced after training for TR (∼19ms, p<0.05) and UTR (∼17ms, p<0.05) with no significant changes for CTR. No effects of training for CPLEN and medial–lateral CPSPD were found. Furthermore, the EMGTP of UTR was predominantly greater before training (∼17ms, p<0.05). However, after training the EMGTP was similar among limbs. These results suggest that concomitant with improved balance recovery and neuromuscular reactions in TR, there is also a cross-education effect in UTR, which might be predominantly related to supraspinal adaptations shared between interconnected structures in the brain.

Cross-over Muscular Adaptation to Blood Flow–Restricted Exercise

Dear Editor-in-Chief: We read with interest the article published by Weatherholt et al. (7). The authors performed a well-controlled study that adds to our knowledge about blood flow–restricted exercise. With their within-subject design, the authors observed similar increases in upper arm muscle cross-sectional area (mCSA) and strength after 8 wk of low load unilateral elbow flexion and extension training with and without blood flow restriction (BFR). The authors suggest that the adaptations for both muscle strength and hypertrophy observed in the limb trained without BFR are attributable to a cross-education effect. Although unilateral training with a high load can increase muscular strength in the untrained, contralateral limb (6), we feel it is likely that the training adaptations observed in the limb trained without BFR are due to the local training stimulus itself. The authors’ reason for suggesting a neural cross-education effect is that training with a low load “is generally accepted as being too low to cause strength increases” (7). Although evidence suggests that high-load training does produce greater increases in strength compared with low-load training, it is clear that low-load training will increase maximal strength to an extent (1). Moreover, other studies using a within-subject design have shown greater increases in muscular strength in a limb trained under BFR compared with the contralateral limb trained without BFR (5). This suggests that increases in strength in one limb are not always equivalent in the contralateral limb. The similar increases in muscular strength observed in both the BFR- and non–BFR-trained limb in the present study are likely attributable to similar increases in mCSA (7). With respect to the author’s second conclusion, a systemic effect of BFR resistance training causing anabolic hormone-induced hypertrophy of the contralateral limb, we suggest that the increase in mCSA of the non–BFR-trained limb is likely due to the local training stimulus itself. Although BFR knee extensor and flexor exercise has been shown to enhance training-induced hypertrophy of the elbow flexors (3), the acute anabolic hormonal response causing such adaptation is questionable. In contrast to the aforementioned study, West et al. (8) have shown that exercise-induced increases in anabolic hormones do not enhance training-induced hypertrophy of the elbow flexors. Furthermore, elbow flexor exercise alone is unable to cause an acute rise in such hormones (8). In the present investigation (7), it is unlikely that such a low volume of unilateral elbow flexor and extensor exercise, even with BFR, would be able to increase such hormones. It is likely that 8 wk of low-load training without BFR was capable of inducing muscle hypertrophy because low-load training without BFR has been shown previously to induce muscle hypertrophy (2,4). This commentary should not be taken as criticism of the study; we offer another possible explanation for the muscular adaptations observed with low-load training without BFR. Similar training adaptations to different unilateral training protocols should not necessarily be attributed to a cross-over effect. C.A. Fahs has received a grant from the American College of Sports Medicine for doctoral research in Kaatsu methodology (#012012).

Effect of Unilateral E‐Stim on Strength in a Contralateral Untrained Limb After Bilateral Strength Training

Unilateral strength training or electrical stimulation increases strength in an untrained, contralateral limb. This cross education effect is similar to conventional training. We have shown reduced strength loss in a contralateral untrained limb with unilateral strength training after 4 weeks of bilateral leg extension training.MethodsIn a pre‐and post‐test design, 18 subjects, aged 18–35, not engaged in structured strength training for 3 months, were randomly assigned to a unilateral strength training (U), e‐stim training (E), or control group(C). All subjects underwent 4 weeks of bilateral leg extension training, then for 4 weeks, either stopped training, or trained the right limb with strength training or e‐stim. A pre‐training, 4 week post‐training and final unilateral 1 RM for leg extension was obtained.ResultsAfter 4 weeks of bilateral training, unilateral 1 RM strength significantly increased (left leg p=0.001; right leg p=0.000). However, during the final 4 weeks, all subjects lost strength in the trained and untrained limbs. The percent change in the untrained and trained limbs respectively were: Group E −4.23%; −1.20%; Group U −6.05%; −0.78% and Group C −8.47%; −6.55%.ConclusionAt these training loads, neither unilateral strength training or e‐stim had a significant effect on the trained or untrained limb, and therefore were unable to prevent strength loss in either limb.

Cross-Education for Improving Strength and Mobility After Distal Radius Fractures: A Randomized Controlled Trial

ObjectiveTo evaluate the effects of cross-education (contralateral effect of unilateral strength training) during recovery from unilateral distal radius fractures on muscle strength, range of motion (ROM), and function. DesignRandomized controlled trial (26-wk follow-up). SettingHospital, orthopedic fracture clinic. ParticipantsWomen older than 50 years with a unilateral distal radius fracture. Fifty-one participants were randomized and 39 participants were included in the final data analysis. InterventionsParticipants were randomized to standard rehabilitation (Control) or standard rehabilitation plus strength training (Train). Standard rehabilitation included forearm casting for 40.4±6.2 days and hand exercises for the fractured extremity. Nonfractured hand strength training for the training group began immediately postfracture and was conducted at home 3 times/week for 26 weeks. Main Outcome MeasuresThe primary outcome measure was peak force (handgrip dynamometer). Secondary outcomes were ROM (flexion/extension; supination/pronation) via goniometer and the Patient Rated Wrist Evaluation questionnaire score for the fractured arm. ResultsFor the fractured hand, the training group (17.3±7.4kg) was significantly stronger than the control group (11.8±5.8kg) at 12 weeks postfracture (P<.017). There were no significant strength differences between the training and control groups at 9 (12.5±8.2kg; 11.3±6.9kg) or 26 weeks (23.0±7.6kg; 19.6±5.5kg) postfracture, respectively. Fractured hand ROM showed that the training group had significantly improved wrist flexion/extension (100.5°±19.2°) than the control group (80.2°±18.7°) at 12 weeks postfracture (P<.017). There were no significant differences between the training and control groups for flexion/extension ROM at 9 (78.0°±20.7°; 81.7°±25.7°) or 26 weeks (104.4°±15.5°; 106.0°±26.5°) or supination/pronation ROM at 9 (153.9°±23.9°; 151.8°±33.0°), 12 (170.9°±9.3°; 156.7°±20.8°) or 26 weeks (169.4°±11.9°; 162.8°±18.1°), respectively. There were no significant differences in Patient Rated Wrist Evaluation questionnaire scores between the training and control groups at 9 (54.2±39.0; 65.2±28.9), 12 (36.4±37.2; 46.2±35.3), or 26 weeks (23.6±25.6; 19.4±16.5), respectively. ConclusionsStrength training for the nonfractured limb after a distal radius fracture was associated with improved strength and ROM in the fractured limb at 12 weeks postfracture. These results have important implications for rehabilitation strategies after unilateral injuries.

Effects of Different Strength Training on Muscle Architecture: Clinical and Ultrasonographic Evaluation in Knee Osteoarthritis

Different strengthening exercises are generally prescribed to overcome the undesirable effects of decreased muscular function on the osteoarthritic joint. Although a few studies have shown the effects of strengthening on the muscle structure in healthy individuals, the literature lacks relevant data concerning knee osteoarthritis. To evaluate the effects of different exercises on quadriceps muscle strength and structure in persons with knee osteoarthritis. A randomized controlled study. Physical medicine and rehabilitation department of a university hospital. Sixty-one patients with knee osteoarthritis were randomly assigned into 6 exercise groups (isometric right/left, isotonic right/left, isokinetic right/left). Subjects were evaluated for pain and functional status with use of the visual analog pain scale, Western Ontario and McMaster Universities Arthritis Index, 50-step walking, and single-leg stance tests before and after 15 sessions of physical therapy. Isokinetic tests were performed at 60° per second. Ultrasonographic measurements for pennation angle, fascicle length, and muscle thickness were performed from the vastus lateralis muscles bilaterally. Increased knee extensor strength was observed bilaterally in the isometric group (P < .01). In the same group, fascicle length and muscle thickness on the strengthened side (P < .01) and fascicle length on the contralateral side (P < .05) were increased. In the isokinetic group, muscle thickness bilaterally and fascicle length on the contralateral side increased (all P < .05). In the isotonic group, muscle thickness increased bilaterally (P < .05). These findings showed that isometric quadriceps training resulted in bilateral strengthening and that accompanying increase in muscle thickness and fascicle length in the same group was consistent with the strength improvement. In this study we evaluated the effects of different strength training on muscle strength and architecture in patients with knee osteoarthritis by using isokinetic measurements and ultrasound. Our results suggest that exercises may influence the muscle architecture in patients with knee osteoarthritis. To our knowledge, this study is the first to demonstrate the effects of cross-education on muscle architecture.

High-intensity unilateral dorsiflexor resistance training results in bilateral neuromuscular plasticity after stroke

Hemiparesis after stroke decreases ability to dorsiflex the more-affected ankle during walking. Increased strength would be beneficial, but the more-affected limb is often too weak to be trained. In neurologically intact participants, training one limb induces strength gains in the contralateral, untrained limb. This approach remains unexplored post-stroke. The aim of this study was to test the hypothesis that unilateral dorsiflexor high-intensity resistance training on the less-affected side increases strength and motor output bilaterally following stroke. 19 participants (84.1 ± 77.6 months post-infarct) performed 6 weeks of maximal isometric dorsiflexion training using the less-affected leg. Voluntary isometric strength (dorsiflexion torque, muscle activation), reciprocal inhibition (RI), walking ability (gait speed, kinematics, EMG patterns), and clinical function were measured within 1 week before and 4 days following training. Post-intervention, dorsiflexion torque increased by ~31 % (p < 0.05) in the more-affected (untrained) and by ~34 % (p < 0.05) in the less-affected (trained) legs. Muscle activation significantly increased bilaterally, by ~59 and ~20 % in the trained and untrained legs, respectively. Notably, 4 participants who were unable to generate functional dorsiflexion on the more-affected side before training could do so post-intervention. Significant correlations between muscle activation and size of RI were noted across muscle groups before and after training, and the relation between size of RI and level of muscle activation in the more-affected tibialis anterior muscle was significantly altered by training. Thus, significant gains in voluntary strength and muscle activation on the untrained, more-affected side after stroke can be invoked through training the opposite limb. We demonstrate residual plasticity existing many years post-stroke and suggest clinical application of the cross-education effect where training the more-affected limb is not initially possible.

What Has Transcranial Magnetic Stimulation Taught Us About Neural Adaptations To Strength Training? A Brief Review

The evidence for neural mechanisms underpinning rapid strength increases has been investigated and discussed for over 30 years using indirect methods, such as surface electromyography, with inferences made toward the nervous system. Alternatively, electrical stimulation techniques such as the Hoffman reflex, volitional wave, and maximal wave have provided evidence of central nervous system changes at the spinal level. For 25 years, the technique of transcranial magnetic stimulation (TMS) has allowed for noninvasive supraspinal measurement of the human nervous system in a number of areas such as fatigue, skill acquisition, clinical neurophysiology, and neurology. However, it has only been within the last decade that this technique has been used to assess neural changes after strength training. The aim of this brief review is to provide an overview of TMS, discuss specific strength training studies that have investigated changes, after short-term strength training in healthy populations in upper and lower limbs, and conclude with further research suggestions and the application of this knowledge for the strength and conditioning coach.