Untrained Limb Research Articles

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.

Effect of Contralateral Strength Training on Muscle Weakness in People With Multiple Sclerosis: Proof-of-Concept Case Series.

The contralateral strength training (CST) effect is a transfer of muscle performance to the untrained limb following training of the contralateral side. The aim of this study was to explore, in individuals with multiple sclerosis (MS) presenting marked lower limb strength asymmetry, the effectiveness of CST on management of muscle weakness of the more-affected limb following training of the less-affected limb. A single-subject research design was used. Eight individuals with MS underwent 16 to 18 high-intensity training sessions of the less-affected ankle dorsiflexor muscles. The primary outcome measure of this single-system case series was maximal strength expressed as peak moment and maximal work. Secondary outcome measures were: Six-Minute-Walk Test, Timed "Up & Go" Test, 10-Meter Timed Walk Test, and Multiple Sclerosis Quality of Life-54 questionnaire. After the 6-week intervention, the contralateral more affected (untrained) limb showed a 22% to 24% increase in maximal strength. From pretest-posttest measurements, participants also performed significantly better on the clinical and functional secondary outcome measures. At the 12-week follow-up, the strength levels of the weaker untrained limb remained significantly superior to baseline levels in the majority (5 out of 8) of the outcome parameters. Considering the design used, the absence of a control group, and the sample size, these findings should be cautiously generalized and will need confirmation in a properly planned randomized controlled trial. The present proof-of-concept study shows, for the first time, the occurrence of the CST effect on muscle performance of ankle dorsiflexor muscles in people with MS. These preliminary findings reveal new potential implications for CST as a promising rehabilitation approach to those conditions where unilateral muscle weakness does not allow or makes difficult performing conventional strength training of the weaker limb.

Enhanced crosslimb transfer of force-field learning for dynamics that are identical in extrinsic and joint-based coordinates for both limbs.

Humans are able to adapt their motor commands to make accurate movements in novel sensorimotor environments, such as when wielding tools that alter limb dynamics. However, it is unclear to what extent sensorimotor representations, obtained through experience with one limb, are available to the opposite, untrained limb and in which form they are available. Here, we compared crosslimb transfer of force-field compensation after participants adapted to a velocity-dependent curl field, oriented either in the sagittal or the transverse plane. Due to the mirror symmetry of the limbs, the force field had identical effects for both limbs in joint and extrinsic coordinates in the sagittal plane but conflicting joint-based effects in the transverse plane. The degree of force-field compensation exhibited by the opposite arm in probe trials immediately after initial learning was significantly greater after sagittal (26 ± 5%) than transverse plane adaptation (9 ± 4%; P < 0.001), irrespective of whether participants learned initially with the left or the right arm or via abrupt or gradual exposure to the force field. Thus transfer was impaired when the orientation of imposed dynamics conflicted in intrinsic coordinates for the two limbs. The data reveal that neural representations of novel dynamics are only partially available to the opposite limb, since transfer is incomplete even when force-field perturbation is spatially compatible for the two limbs, according to both intrinsic and extrinsic coordinates.

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.

The effect of training of the non-dominant knee muscles on ipsi- and contralateral strength gains

BACKGROUND: Although transfer of unilateral training has been quite widely explored, few studies have focused on gains achieved due to concentric isokinetic training of the non-dominant side. OBJECTIVE: To examine the effects of unilateral non-dominant (ND) isokinetic knee extension and flexion training at 60◦/s on ipsilateral and contralateral knee extension and flexion peak moment (PM) in active female population as well investigate the speed specificity nature of this protocol. METHODS: Thirty female were divided into two groups: experimental and control. The experimental group trained concentrically the ND flexors and extensors at 60◦/s according to the following protocol: 5–6 reps X 2–4 sets X 3d X 4w at 100% effort while PM at preand post-training was tested concentrically at 60 and 180◦/s. RESULTS: Significant (p < 0.05) increases in the extensors and flexors PM peak moment in both the trained and untrained limb were noted in the experimental group, ranging 19–27% and 12–17%, respectively. The effects were speed specific in the trained but not in untrained limb. No changes were noted in the PM of the control group. CONCLUSIONS: In physically active female population, concentric isokinetic training of the ND knee extensors and flexors at 60◦/s significantly increase the strength of these muscles at the trained and untrained limb. This cross-education was not speed specific and therefore may obviate the need to use a multiple speed protocol.

Increased cross-education of muscle strength and reduced corticospinal inhibition following eccentric strength training

Aim: Strength training of one limb results in a substantial increase in the strength of the untrained limb, however, it remains unknown what the corticospinal responses are following either eccentric or concentric strength training and how this relates to the cross-education of strength. The aim of this study was to determine if eccentric or concentric unilateral strength training differentially modulates corticospinal excitability, inhibition and the cross-transfer of strength. Methods: Changes in contralateral (left limb) concentric strength, eccentric strength, motor-evoked potentials, short-interval intracortical inhibition and silent period durations were analyzed in groups of young adults who exercised the right wrist flexors with either eccentric (N=9) or concentric (N=9) contractions for 12 sessions over 4weeks. Control subjects (N=9) did not train. Results: Following training, both groups exhibited a significant strength gain in the trained limb (concentric group increased concentric strength by 64% and eccentric group increased eccentric strength by 62%) and the extent of the cross-transfer of strength was 28% and 47% for the concentric and eccentric group, respectively, which was different between groups (P=0.031). Transcranial magnetic stimulation revealed that eccentric training reduced intracortical inhibition (37%), silent period duration (15–27%) and increased corticospinal excitability (51%) compared to concentric training for the untrained limb (P=0.033). There was no change in the control group. Conclusion: The results show that eccentric training uniquely modulates corticospinal excitability and inhibition of the untrained limb to a greater extent than concentric training. These findings suggest that unilateral eccentric contractions provide a greater stimulus in cross-education paradigms and should be an integral part of the rehabilitative process following unilateral injury to maximize the response.

Intermanual transfer and bilateral cortical plasticity is maintained in older adults after skilled motor training with simple and complex tasks.

Intermanual transfer refers to the phenomenon whereby unilateral motor training induces performance gains in both the trained limb and in the opposite, untrained limb. Evidence indicates that intermanual transfer is attenuated in older adults following training on a simple ballistic movement task, but not after training on a complex task. This study investigated whether differences in plasticity in bilateral motor cortices underlie these differential intermanual transfer effects in older adults. Twenty young (<35 years-old) and older adults (>65 years) trained on a simple (repeated ballistic thumb abduction) and complex (sequential finger-thumb opposition) task in separate sessions. Behavioral performance was used to quantify intermanual transfer between the dominant (trained) and non-dominant (untrained) hands. The amplitude of motor-evoked potentials induced by single pulse transcranial magnetic stimulation was used to investigate excitability changes in bilateral motor cortices. Contrary to predictions, both age groups exhibited performance improvements in both hands after unilateral skilled motor training with simple and complex tasks. These performance gains were accompanied by bilateral increases in cortical excitability in both groups for the simple but not the complex task. The findings suggest that advancing age does not necessarily influence the capacity for intermanual transfer after training with the dominant hand.

Inter-limb transfer of both simple and complex motor skills is maintained in elderly adults

Inter-limb transfer refers to the phenomenon whereby unilateral motor-skill training induces performance gains in both the trained limb and in the opposite, untrained limb. Evidence indicates that older adults exhibit a reduction in the capacity for inter-limb transfer following training on a simple ballistic movement task, but not after training on a complex task. Evidence also suggests that age-related over-activity in bilateral motor cortices may underlie the differential inter-limb transfer evident after simple and complex tasks in elderly adults.

The effects of anodal-tDCS on cross-limb transfer in older adults

ObjectiveAge-related neurodegeneration may interfere with the ability to respond to cross-limb transfer, whereby bilateral performance improvements accompany unilateral practice. We investigated whether transcranial direct current stimulation (tDCS) would facilitate this phenomena in older adults. Methods12 young and 12 older adults underwent unilateral visuomotor tracking (VT), with anodal or sham-tDCS over the ipsilateral motor cortex. Transcranial magnetic stimulation (TMS) assessed motor evoked potentials (MEPs) and short interval intracortical inhibition (SICI). Performance was quantified through a VT error. Variables were assessed bilaterally at baseline and post-intervention. ResultsThe trained limb improved performance, facilitated MEPs and released SICI in both age groups. In the untrained limb, VT improved in young for both sham and anodal-tDCS conditions, but only following anodal-tDCS for the older adults. MEPs increased in all conditions, except the older adult’s receiving sham. SICI was released in both tDCS conditions for young and old. ConclusionFollowing a VT task, older adults still display use-dependent plasticity. Although no significant age-related differences between the outcome measures, older adults exhibited significant cross-limb transfer of performance following anodal-tDCS, which was otherwise absent following motor practice alone. SignificanceThese findings provide clinical implications for conditions restricting the use of one limb, such as stroke.

Inter-limb generalization of visuomotor adaptation is more automatic when the perturbation is aligned in extrinsic and joint-based coordinates

Event Abstract Back to Event Inter-limb generalization of visuomotor adaptation is more automatic when the perturbation is aligned in extrinsic and joint-based coordinates Timothy Carroll1*, Eugene Poh1, Tania Duarte Ferreira1 and Aymar De Rugy1, 2 1 The University of Queensland, School of Human Movement Studies, Australia 2 Université Bordeaux Segalen, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, France Many questions remain regarding how and why new visuomotor maps obtained with one limb can benefit the other. In an isometric aiming context, we recently found strong, immediate transfer of adaptation between limbs for a sagittal plane workspace where the visuomotor distortion had identical effects in eye- and joint-based coordinates bilaterally, but no transfer in a frontal plane workspace where an identical visual distortion had opposite effects for the two limbs in joint-based coordinates. This suggests that mixed transfer results reported previously for reaching tasks in the horizontal plane might be explained by coordinate frame conflicts associated with the mirror symmetry of the limbs. Here we compared cross-limb transfer of adaptation to visuomotor rotation (45 deg) in a planar reaching task (16 targets) when the limb and visual feedback were oriented in the sagittal (n=8) or the horizontal plane (n=8). Each person completed two sessions in counterbalanced order; one to assess transfer from the right arm to the left and another from left to right. There was significant transfer of feedforward performance to the untrained limb in both horizontal and sagittal conditions (angular error at 20% of target distance: Sagittal = 45%, Horizontal = 18%), but transfer of overall reach performance was significantly greater for the Sagittal than Horizontal group (total path length to target: Sagittal = 58%, Horizontal = 30%. Moreover, reaction times were significantly higher during the first trials in the transfer phase for horizontal than sagittal groups (497 ms versus 380 ms), suggesting a greater cognitive component to horizontal plane error reduction. The results contrast markedly with previous data for isometric force aiming and reaching with veridical, virtual reality feedback, which suggests that the location of the visual display relative to the physical workspace critically influences transfer of new visuomotor maps to the opposite limb. Keywords: reaching, motor learning, visuomotor rotation, Sensorimotor adaptation, Hemispheric asymmetries, Inter-limb Transfer Conference: XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014. Presentation Type: Poster Topic: Motor Behaviour Citation: Carroll T, Poh E, Duarte Ferreira T and De Rugy A (2015). Inter-limb generalization of visuomotor adaptation is more automatic when the perturbation is aligned in extrinsic and joint-based coordinates. Conference Abstract: XII International Conference on Cognitive Neuroscience (ICON-XII). doi: 10.3389/conf.fnhum.2015.217.00072 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Feb 2015; Published Online: 24 Apr 2015. * Correspondence: Prof. Timothy Carroll, The University of Queensland, School of Human Movement Studies, Brisbane, Australia, timothy.carroll@uq.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Timothy Carroll Eugene Poh Tania Duarte Ferreira Aymar De Rugy Google Timothy Carroll Eugene Poh Tania Duarte Ferreira Aymar De Rugy Google Scholar Timothy Carroll Eugene Poh Tania Duarte Ferreira Aymar De Rugy PubMed Timothy Carroll Eugene Poh Tania Duarte Ferreira Aymar De Rugy Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Relationship between improvements in motor performance and changes in anticipatory postural adjustments during whole-body reaching training

Anticipatory postural adjustments (APAs) provide postural stability and play an important role in ensuring appropriate motor performance. APAs also change in various situations. However, it is unknown whether changes in APAs during repetitive movement training contribute to improvement in motor performance. This study aimed to investigate the relationship between improvement in motor performance and changes in APAs during repeated reaching training, as well as the learning effects on APA changes. Sixteen healthy subjects (23±2years of age) stood barefoot on a force platform and reached as quickly and accurately as possible to a target placed at their maximum reach distance immediately following a beep signal in a reaction time condition. Whole-body reaching training with the right arm was repeated 100 times for three consecutive days. Motor performance and APAs were evaluated on the first day, after discontinuation of training for one day, and again at three months. In addition, reaching with the left arm (untrained limb) was tested on the first and the fifth training day. Body position segments were measured using three-dimensional motion analysis. Surface electromyography of eight postural muscles in both lower limbs was recorded. Kinetics data were recorded using the force platform. Whole-body reaching training induced not only improvements in motor performance (e.g., increased peak hand velocity), but also changes in APAs (e.g., earlier APA onset and increased amplitude). These changes were strongly correlated with and occurred earlier than improvements in motor performance. The learning effects on APAs were retained after the discontinuation of training and were generalized to the untrained limb. These results suggest that change in APAs contributes to improvement in motor performance; that is, the central nervous system may be able to adapt APAs for improvement in motor performance.

Anodal-tDCS applied during unilateral strength training increases strength and corticospinal excitability in the untrained homologous muscle.

Evidence suggests that the cross-transfer of strength following unilateral training may be modulated by increased corticospinal excitability of the ipsilateral primary motor cortex, due to cross-activation. Anodal-tDCS (a-tDCS) has been shown to acutely increase corticospinal excitability and motor performance, which may enhance this process. Therefore, we sought to examine changes in neural activation and strength of the untrained limb following the application of a-tDCS during a single unilateral strength training session. Ten participants underwent three conditions in a randomized, double-blinded crossover design: (1) strength training + a-tDCS, (2) strength training + sham-tDCS and (3) a-tDCS alone. a-tDCS was applied for 20 min at 2 mA over the right motor cortex. Unilateral strength training of the right wrist involved 4 × 6 wrist extensions at 70 % of maximum. Outcome measures included maximal voluntary strength, corticospinal excitability, short-interval intracortical inhibition, and cross-activation. We observed a significant increase in strength of the untrained wrist (5.27 %), a decrease in short-interval intracortical inhibition (-13.49 %), and an increase in cross-activation (15.71 %) when strength training was performed with a-tDCS, but not following strength training with sham-tDCS, or tDCS alone. Corticospinal excitability of the untrained wrist increased significantly following both strength training with a-tDCS (17.29 %), and a-tDCS alone (15.15 %), but not following strength training with sham-tDCS. These findings suggest that a single session of a-tDCS combined with unilateral strength training of the right limb increases maximal strength and cross-activation to the contralateral untrained limb.

UNILATERAL LOWER LIMBS STRENGTH TRAINING WITH THERA-BAND® ELASTIC RESISTANCE BANDS IMPROVES FUNCTIONAL ABILITY AND BALANCE OF THE UNTRAINED CONTRALATERAL LIMB

BackgroundCross-education (CE) is being studied for several decades and refers to the power transfer and proprioception in untrained limb after training of the homologous contralateral limb.ObjectiveTo examine whether unilateral strengthening...

Cross-Limb Interference during Motor Learning

It is well known that following skill learning, improvements in motor performance may transfer to the untrained contralateral limb. It is also well known that retention of a newly learned task A can be degraded when learning a competing task B that takes place directly after learning A. Here we investigate if this interference effect can also be observed in the limb contralateral to the trained one. Therefore, five different groups practiced a ballistic finger flexion task followed by an interfering visuomotor accuracy task with the same limb. Performance in the ballistic task was tested before the training, after the training and in an immediate retention test after the practice of the interference task for both the trained and the untrained hand. After training, subjects showed not only significant learning and interference effects for the trained limb but also for the contralateral untrained limb. Importantly, the interference effect in the untrained limb was dependent on the level of skill acquisition in the interfering motor task. These behavioural results of the untrained limb were accompanied by training specific changes in corticospinal excitability, which increased for the hemisphere ipsilateral to the trained hand following ballistic training and decreased during accuracy training of the ipsilateral hand. The results demonstrate that contralateral interference effects may occur, and that interference depends on the level of skill acquisition in the interfering motor task. This finding might be particularly relevant for rehabilitation.

Evaluation of lactic acid transfer to contralateral hand with two different type muscle contraction

This study is conducted with the aim of investigating the effect of two kind of muscle contraction on generating lactic acid in a limb and investigating the effect of that on the amount of lactic acid in the contralateral limb. In a favor of the study objective, the subjects were university students who are not athlete. The subjects consists of 12 students male between 20-22 years old)21.8± 4.12 (who has not a regular sport history over the past two years. First of all, the amount of lactic acid in active and non-active hand at the rest time before exercise was measured. Then in two separate steps the subjects’ analysis was carried out. In the first and second stage (next day) 70% of maximum muscle strength was estimated and the first stage by choosing the suitable weight, the action of holding at the angle of 90 degree with isometric contraction and in the second stage the action of elbows bent and open with isotonic contraction to the extent of fatigue was carried out. Immediately after completion of the aforesaid activities the amount of lactic acid in active and non-active hand was measured and registered. The data were analyzed by using correlation t-test and the result of research showed that after isometric contraction more lactate is accumulated in the active muscles than isotonic contraction and also in the Statistical test there was no significant difference in the above case. By considering that the measurement of lactic acid in the non-active limb was done immediately after the completion of training, the results indicate that the transfer of lactate in the blood to the non-active limb is not that much which can affect the limb. Results from this study do not approve the effects of accumulated lactic acid on active limb and the transfer of that to the non-active limb and it’s inconsistent with the theory of transfer of power and muscular endurance from trained limb to untrained limb (cross transfer theory).

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.

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.

Changes in brain activation patterns according to cross-training effect in serial reaction time task: An functional MRI study.

Cross-training is a phenomenon related to motor learning, where motor performance of the untrained limb shows improvement in strength and skill execution following unilateral training of the homologous contralateral limb. We used functional MRI to investigate whether motor performance of the untrained limb could be improved using a serial reaction time task according to motor sequential learning of the trained limb, and whether these skill acquisitions led to changes in brain activation patterns. We recruited 20 right-handed healthy subjects, who were randomly allocated into training and control groups. The training group was trained in performance of a serial reaction time task using their non-dominant left hand, 40 minutes per day, for 10 days, over a period of 2 weeks. The control group did not receive training. Measurements of response time and percentile of response accuracy were performed twice during pre- and post-training, while brain functional MRI was scanned during performance of the serial reaction time task using the untrained right hand. In the training group, prominent changes in response time and percentile of response accuracy were observed in both the untrained right hand and the trained left hand between pre- and post-training. The control group showed no significant changes in the untrained hand between pre- and post-training. In the training group, the activated volume of the cortical areas related to motor function (i.e., primary motor cortex, premotor area, posterior parietal cortex) showed a gradual decrease, and enhanced cerebellar activation of the vermis and the newly activated ipsilateral dentate nucleus were observed during performance of the serial reaction time task using the untrained right hand, accompanied by the cross-motor learning effect. However, no significant changes were observed in the control group. Our findings indicate that motor skills learned over the 2-week training using the trained limb were transferred to the opposite homologous limb, and motor skill acquisition of the untrained limb led to changes in brain activation patterns in the cerebral cortex and cerebellum.

At‐home resistance tubing strength training increases shoulder strength in the trained and untrained limb

The purpose was to determine if an at-home resistance tubing strength training program on one shoulder (that is commonly used in rehabilitation settings) would produce increases in strength in the trained and untrained shoulders via cross-education. Twenty-three participants were randomized to TRAIN (strength-trained one shoulder; n = 13) or CONTROL (no intervention; n = 10). Strength training was completed at home using resistance tubing and consisted of maximal shoulder external rotation, internal rotation, scaption, retraction, and flexion 3 days/week for 4 weeks. Strength was measured via handheld dynamometry and muscle size measured via ultrasound. For external rotation strength, the trained (10.9 ± 10.9%) and untrained (12.7 ± 9.6%) arm of TRAIN was significantly different than CONTROL (1.6 ± 13.2%; -2.7 ± 12.3%; pooled across arm; P < 0.05). For internal rotation strength, the trained (14.8 ± 11.3%) and untrained (14.6 ± 10.1%) arm of TRAIN was significantly different than CONTROL (6.4 ± 11.2%; 5.1 ± 8.8%; pooled across arm; P < 0.05). There were no significant differences for scaption strength (P = 0.056). TRAIN significantly increased muscle size in the training arm of the supraspinatus (1.90 ± 0.32 to 1.99 ± 0.31 cm), and the anterior deltoid (1.08 ± 0.37 to 1.21 ± 0.39 cm; P < 0.05). This study suggests that an at-home resistance tubing training program on one limb can produce increases in strength in both limbs, and has implications for rehabilitation after unilateral shoulder injuries.

Neural pathways mediating cross education of motor function

Cross education is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb. Despite interest in this phenomenon having been sustained for more than a century, a comprehensive explanation of the mediating neural mechanisms remains elusive. With new evidence emerging that cross education may have therapeutic utility, the need to provide a principled evidential basis upon which to design interventions becomes ever more pressing. Generally, mechanistic accounts of cross education align with one of two explanatory frameworks. Models of the “cross activation” variety encapsulate the observation that unilateral execution of a movement task gives rise to bilateral increases in corticospinal excitability. The related conjecture is that such distributed activity, when present during unilateral practice, leads to simultaneous adaptations in neural circuits that project to the muscles of the untrained limb, thus facilitating subsequent performance of the task. Alternatively, “bilateral access” models entail that motor engrams formed during unilateral practice, may subsequently be utilized bilaterally—that is, by the neural circuitry that constitutes the control centers for movements of both limbs. At present there is a paucity of direct evidence that allows the corresponding neural processes to be delineated, or their relative contributions in different task contexts to be ascertained. In the current review we seek to synthesize and assimilate the fragmentary information that is available, including consideration of knowledge that has emerged as a result of technological advances in structural and functional brain imaging. An emphasis upon task dependency is maintained throughout, the conviction being that the neural mechanisms that mediate cross education may only be understood in this context.