Untrained Limb Research Articles

Ipsilateral corticomotor responses are confined to the homologous muscle following cross-education of muscular strength.

Cross-education of strength occurs when strength-training 1 limb increases the strength of the untrained limb and is restricted to the untrained homologous muscle. Cortical circuits located ipsilateral to the trained limb might be involved. We used transcranial magnetic stimulation (TMS) to determine the corticomotor responses from the untrained homologous (biceps brachii) and nonhomologous (flexor carpi radialis) muscle following strength-training of the right elbow flexors. Motor evoked potentials were recorded from the untrained left biceps brachii and flexor carpi radialis during a submaximal contraction from 20 individuals (10 women, 10 men; aged 18-35 years; training group, n = 10; control group, n = 10) before and after 3 weeks of strength-training the right biceps brachii at 80% of 1-repetition maximum. Recruitment-curves for corticomotor excitability and inhibition of the untrained homologous and nonhomologous muscle were constructed and assessed by examining the area under the recruitment curve. Strength-training increased strength of the trained elbow flexors (29%), resulting in an 18% increase in contralateral strength of the untrained elbow flexors (P < 0.0001). The trained wrist flexors increased by 19%, resulting in a 12% increase in strength of the untrained wrist flexors (P = 0.005). TMS showed increased corticomotor excitability and decreased corticomotor inhibition for the untrained homologous muscle (P < 0.05); however, there were no changes in the untrained nonhomologous muscle (P > 0.05). These findings show that the cross-education of muscular strength is spatially distributed; however, the neural adaptations are confined to the motor pathway ipsilateral to the untrained homologous agonist.

Limb Position Tolerant Pattern Recognition for Myoelectric Prosthesis Control with Adaptive Sparse Representations From Extreme Learning.

We present a robust sparsity-based adaptive classification method that is significantly less sensitive to signal deviations resulting from untrained conditions. We compare this approach in the offline and online contexts of untrained upper-limb positions for amputee and able-bodied subjects to demonstrate its robustness compared against other myoelectric classification methods. We report significant performance improvements () in untrained limb positions across all subject groups. The robustness of our suggested approach helps to ensure better untrained condition performance from fewer training conditions. This method of prosthesis control has the potential to deliver real-world clinical benefits to amputees: better condition-tolerant performance, reduced training burden in terms of frequency and duration, and increased adoption of myoelectric prostheses.

Unilateral leg resistance training improves time to task failure of the contralateral untrained leg

Background: Cross-training is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb, most likely due to neural adaptations at the level of the motor cortex and/or spinal cord. Objective: To investigate whether unilateral resistance training can affect the ability of untrained homologous muscle in the contralateral limb to maintain force output over a sustained contraction. Methods: Fifteen healthy subjects completed 12 weeks of resistance training consisting of 36 sessions, using the unilateral leg press exercise. Sustained isometric knee extension performed at 50% of maximal force until task failure on both the ipsilateral trained leg and contralateral untrained leg. Surface electromyography (EMG) signals were recorded from the trained and contralateral untrained quadriceps (vastus medialis, rectus femoris, and vastus lateralis). Results: Time to task failure of the contralateral untrained leg was significantly increased after 12 weeks of unilateral resistance training (p < .05). Moreover, the EMG amplitude of the contralateral untrained quadriceps was significantly higher during the post training sustained contractions with respect to pre training condition (p < .05). Conclusions: Unilateral resistance training of the quadriceps can increase the ability of homologous muscle in the contralateral limb to maintain force output.

Time to task failure of the contralateral untrained limb after high load-low repetition eccentric and low load-high repetition resistance training

Time to task failure of the contralateral untrained limb after high load-low repetition eccentric and low load-high repetition resistance 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.

Maximal Velocity Adaptions During Unilateral Resistance Training In Older Adults

Maximal velocity parameters are negatively affected by aging; however, little is known regarding the short-term effects of resistance training (RT) on maximal velocity variables in older adults. Furthermore, whether or not unilateral RT induces maximal velocity adaptations in the untrained limb has not been determined. PURPOSE: To examine the effects of unilateral RT on maximal velocity parameters of the ipsilateral and contralateral leg in older males. METHODS: Twenty-one untrained older males were randomly assigned to a training (TG; n = 10, age = 64.70 ± 6.91 yrs.) or control (CG; n = 11, age = 65.56 ± 11.56 yrs.) group. The TG performed 3 sessions per week of unilateral isokinetic RT for 4 weeks. RT sessions consisted of maximal concentric knee extensions at 45°·s-1 for 4 sets of 10 repetitions. Subjects were instructed to “kick out as hard and fast as possible” during each RT session. Maximal concentric isokinetic testing of the knee extensors for the trained (TL) and untrained (UL) leg at 500°·s-1 (ISOK500) was performed before (PRE), at week 2 (MID), and after week 4 (POST) of RT. There was no resistance during ISOK500, with the exception of the lever arm mass, as the velocity was above all subjects’ maximum velocity. The highest velocity attained (PV; deg·s-1) and the linear slope of the velocity-time curve (RVD; deg·s-2) were recorded for analysis. For the TL and UL, one-way repeated measures analyses of variance were used for the TG and CG separately. RESULTS: PV and RVD remained unchanged in both legs for the CG (p > 0.05). PV did not change in the TL (p = 0.084), while RVD increased from PRE to POST (+5.8%; p = 0.029) and MID to POST (+4.1%; p = 0.038). PV (p = 0.644) and RVD (p = 0.523) were unaltered in the UL. CONCLUSION: RVD appears to be more sensitive to change during the early-phase of RT compared to PV in older males. However, neither PV nor RVD in the UL appear to be affected by short-term unilateral RT. Since many neural adaptations are expressed bilaterally, the improvement in RVD for only the training leg suggests the adaptation is more likely mechanical in origin.

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.

Vibration training after chronic spinal cord injury: Evidence for persistent segmental plasticity

H-reflex paired-pulse depression is gradually lost within the first year post-SCI, a process believed to reflect reorganization of segmental interneurons after the loss of normal descending (cortical) inhibition. This reorganization co-varies in time with the development of involuntary spasms and spasticity. The purpose of this study is to determine whether long-term vibration training may initiate the return of H-reflex paired-pulse depression in individuals with chronic, complete SCI. Five men with SCI received twice-weekly vibration training (30Hz, 0.6g) to one lower limb while seated in a wheelchair. The contra-lateral limb served as a within-subject control. Paired-pulse H-reflexes were obtained before, during, and after a session of vibration. Untrained limb H-reflex depression values were comparable to chronic SCI values from previous reports. In contrast, the trained limbs of all 5 participants showed depression values that were within the range of previously-reported Acute SCI and Non-SCI H-reflex depression. The average difference between limbs was 34.98% (p=0.016). This evidence for the return of H-reflex depression suggests that even for people with long-standing SCI, plasticity persists in segmental reflex pathways. The spinal networks involved with the clinical manifestation of spasticity may thus retain adaptive plasticity after long-term SCI. The results of this study indicate that vibration training may hold promise as an anti-spasticity rehabilitation intervention.

P254 The interaction of cross-limb transfer gains, intermittent theta-burst stimulation and subsequent learning in young and older adults

Introduction Recently we found evidence that following right hand motor training intermittent theta-burst stimulation (iTBS) applied to the ipsilateral primary motor cortex (M1) increased corticospinal excitability (CSE) and facilitated performance in the untrained hand (i.e., cross-limb transfer, CLT). Objectives Here we examine whether the interaction of CLT and iTBS can be exploited to drive improved learning in one hand following learning with the other hand, and to assess any age-related differences in this interaction. Materials and methods Eighteen young (Mage = 25.2 ± 5.7 years, 8 males) and seven healthy older adults (Mage = 66.4 ± 3.1 years, 6 males) practiced a ballistic motor task with their right index finger (150 trials, T1), after which iTBS was applied to the untrained M1. Another 150 training trials (T2) were then conducted. During T2, 13 participants (8 young, 7 older) practiced with their left hand (RL group) while 12 young participants continued practicing with their right hand (RR group). Performance (peak acceleration) and CSE were assessed before T1, pre- and post-iTBS, and following T2. Results Although iTBS facilitated untrained hand MEPs in both age groups (+29%, p = .005), untrained hand performance was facilitated by iTBS in young (+25%; p = .04), but not in older (−2%, p = .92), adults. Following T2, no differences in left hand performance gains (adjusted for post-iTBS performance) between RL and RR (12% vs. 9%, p=.88, Fig. 1A) were observed, although CSE gains in the left hand following T2 were greater following RL than RR (34% vs. −4%, p = .02, Fig. 1A). Conclusion In young but not older adults, iTBS-induced LTP-like plasticity can be utilised to drive performance gains in the untrained limb above and beyond those gains already induced by cross-limb transfer processes. With respect to left hand performance gains, no advantage was observed following left hand T2 training (‘training gains’) compared to right hand T2 training (‘CLT gains’). Thus, homeostatic plasticity effects following iTBS administered to the untrained M1 following right hand motor learning appear insufficient to drive greater subsequent training gains when training is then undertaken with the left hand relative to those gains which would continue to occur (during right hand training) as a result of cross-limb transfer. Download : Download high-res image (447KB) Download : Download full-size image

The effects of a single bout of exercise on motor memory interference in the trained and untrained hemisphere

Increasing evidence suggests that cardiovascular exercise has positive effects on motor memory consolidation. In this study, we investigated whether a single session of high-intensity interval training (HIIT) mitigates the effects of practicing an interfering motor task. Furthermore, learning and interference effects were assessed in the actively trained and untrained limb as it is known that unilateral motor learning can cause bilateral adaptations.Subjects performed a ballistic training and then the HIIT either before (HIIT_before) or after (HIIT_after) practicing an interfering accuracy task (AT). The control group (No_HIIT) did not participate in the HIIT but rested instead. Performance in the ballistic task (BT) was tested before and after the ballistic training, after the exercise and practice of the AT and 24h later. After ballistic training, all groups showed comparable increases in performance in the trained and untrained limb. Despite the practice of the AT, HIIT_before maintained their BT performance after the high-intensity interval training whereas HIIT_after (trend) & No_HIIT showed prominent interference effects. After 24h, HIIT_before still did not show any interference effects but further improved ballistic motor performance. HIIT_after counteracted the interference resulting in a comparable BT performance after 24h than directly after the ballistic training while No_HIIT had a significantly lower BT performance in the retention test. The results were similar in the trained and untrained limb. The current results imply that a single session of cardiovascular exercise can prevent motor interference in the trained and untrained hemisphere. Overall learning was best, and interference least, when HIIT was performed before the interfering motor task.

Structural and Functional Cortical Connectivity Mediating Cross Education of Motor Function.

Cross-education (CE) is the process whereby training with one limb leads to subsequent improvement in performance by the opposite untrained limb. We used multimodal neuroimaging in humans to investigate the mediating neural mechanisms by relating quantitative estimates of functional and structural cortical connectivity to individual levels of interlimb transfer. Resting-state (rs)-fMRI and diffusion weighted imaging (DWI) scans were undertaken before unilateral ballistic wrist flexion training. The rs-fMRI sequence was repeated immediately afterward. The increase in performance of the untrained limb was 83.6% of that observed for the trained limb and significantly greater than that of a control group who undertook no training. Functional connectivity in the resting motor network between right and left supplementary motor areas (SMA) was elevated after training. These changes were not, however, correlated with individual levels of transfer. Analysis of the DWI data using constrained spherical deconvolution-based tractography indicated that fractional anisotropy and apparent fiber density in tracts connecting bilateral SMA were negatively correlated with and predictive of transfer. The findings suggest that interhemispheric interactions between bilateral SMA play an instrumental role in CE and that the structural integrity of the connecting white matter pathways influences the level of transfer.SIGNIFICANCE STATEMENT Strength or skill training with one limb also brings about improvements in the performance of the opposite, untrained limb. This phenomenon, termed cross-education (CE), has obvious potential for the rehabilitation of functional capacity that has been lost through brain insult or musculoskeletal injury. The neural mechanisms that give rise to CE are, however, poorly understood. We used a combination of neuroimaging methods to investigate the pathways in the human brain that mediate CE. We determined that the supplementary motor area (SMA) plays an important role in the interlimb transfer of performance gains and demonstrate that the quality of the white matter fibers connecting right and left SMA predicts the benefit that an individual derives from CE.

Cross-education of wrist extensor strength is not influenced by non-dominant training in right-handers

Cross-education of strength has been proposed to be greater when completed by the dominant limb in right handed humans. We investigated whether the direction of cross-education of strength and corticospinal plasticity are different following right or left limb strength training in right-handed participants. Changes in strength, muscle thickness and indices of corticospinal plasticity were analyzed in 23 adults who were exposed to 3-weeks of either right-hand strength training (RHT) or left-hand strength training (LHT). Maximum voluntary wrist extensor strength in both the trained and untrained limb increased, irrespective of which limb was trained, with TMS revealing reduced corticospinal inhibition. Cross-education of strength was not limited by which limb was trained and reduced corticospinal inhibition was not just confined to the trained limb. Critically, from a behavioral perspective, the magnitude of cross-education was not limited by which limb was trained.

Effect of coordinate frame compatibility on the transfer of implicit and explicit learning across limbs.

Insights into the neural representation of motor learning can be obtained by investigating how learning transfers to novel task conditions. We recently demonstrated that visuomotor rotation learning transferred strongly between left and right limbs when the task was performed in a sagittal workspace, which afforded a consistent remapping for the two limbs in both extrinsic and joint-based coordinates. In contrast, transfer was absent when performed in horizontal workspace, where the extrinsically defined perturbation required conflicting joint-based remapping for the left and right limbs. Because visuomotor learning is thought to be supported by both implicit and explicit forms of learning, however, it is unclear to what extent these distinct forms of learning contribute to interlimb transfer. In this study, we assessed the degree to which interlimb transfer, following visuomotor rotation training, reflects explicit vs. implicit learning by obtaining verbal reports of participants' aiming direction before each movement. We also determined the extent to which these distinct components of learning are constrained by the compatibility of coordinate systems by comparing transfer between groups of participants who reached to targets arranged in the horizontal and sagittal planes. Both sagittal and horizontal conditions displayed complete transfer of explicit learning to the untrained limb. In contrast, transfer of implicit learning was incomplete, but the sagittal condition showed greater transfer than the horizontal condition. These findings suggest that explicit strategies developed with one limb can be fully implemented in the opposite limb, whereas implicit transfer depends on the degree to which new sensorimotor maps are spatially compatible for the two limbs.

Motor learning and cross-limb transfer rely upon distinct neural adaptation processes.

Performance benefits conferred in the untrained limb after unilateral motor practice are termed cross-limb transfer. Although the effect is robust, the neural mechanisms remain incompletely understood. In this study we used noninvasive brain stimulation to reveal that the neural adaptations that mediate motor learning in the trained limb are distinct from those that underlie cross-limb transfer to the opposite limb. Thirty-six participants practiced a ballistic motor task with their right index finger (150 trials), followed by intermittent theta-burst stimulation (iTBS) applied to the trained (contralateral) primary motor cortex (cM1 group), the untrained (ipsilateral) M1 (iM1 group), or the vertex (sham group). After stimulation, another 150 training trials were undertaken. Motor performance and corticospinal excitability were assessed before motor training, pre- and post-iTBS, and after the second training bout. For all groups, training significantly increased performance and excitability of the trained hand, and performance, but not excitability, of the untrained hand, indicating transfer at the level of task performance. The typical facilitatory effect of iTBS on MEPs was reversed for cM1, suggesting homeostatic metaplasticity, and prior performance gains in the trained hand were degraded, suggesting that iTBS interfered with learning. In stark contrast, iM1 iTBS facilitated both performance and excitability for the untrained hand. Importantly, the effects of cM1 and iM1 iTBS on behavior were exclusive to the hand contralateral to stimulation, suggesting that adaptations within the untrained M1 contribute to cross-limb transfer. However, the neural processes that mediate learning in the trained hemisphere vs. transfer in the untrained hemisphere appear distinct.

Neural Adaptations Associated with Interlimb Transfer in a Ballistic Wrist Flexion Task.

Cross education is the process whereby training of one limb gives rise to increases in the subsequent performance of its opposite counterpart. The execution of many unilateral tasks is associated with increased excitability of corticospinal projections from primary motor cortex (M1) to the opposite limb. It has been proposed that these effects are causally related. Our aim was to establish whether changes in corticospinal excitability (CSE) arising from prior training of the opposite limb determine levels of interlimb transfer. We used three vision conditions shown previously to modulate the excitability of corticospinal projections to the inactive (right) limb during wrist flexion movements performed by the training (left) limb. These were: (1) mirrored visual feedback of the training limb; (2) no visual feedback of either limb; and (3) visual feedback of the inactive limb. Training comprised 300 discrete, ballistic wrist flexion movements executed as rapidly as possible. Performance of the right limb on the same task was assessed prior to, at the mid point of, and following left limb training. There was no evidence that variations in the excitability of corticospinal projections (assessed by transcranial magnetic stimulation (TMS)) to the inactive limb were associated with, or predictive of, the extent of interlimb transfer that was expressed. There were however associations between alterations in muscle activation dynamics observed for the untrained limb, and the degree of positive transfer that arose from training of the opposite limb. The results suggest that the acute adaptations that mediate the bilateral performance gains realized through unilateral practice of this ballistic wrist flexion task are mediated by neural elements other than those within M1 that are recruited at rest by single-pulse TMS.

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.

Muscle, functional and cognitive adaptations after flywheel resistance training in stroke patients: a pilot randomized controlled trial.

BackgroundResistance exercise (RE) improves neuromuscular function and physical performance after stroke. Yet, the effects of RE emphasizing eccentric (ECC; lengthening) actions on muscle hypertrophy and cognitive function in stroke patients are currently unknown. Thus, this study explored the effects of ECC-overload RE training on skeletal muscle size and function, and cognitive performance in individuals with stroke.MethodsThirty-two individuals with chronic stroke (≥6 months post-stroke) were randomly assigned into a training group (TG; n = 16) performing ECC-overload flywheel RE of the more-affected lower limb (12 weeks, 2 times/week; 4 sets of 7 maximal closed-chain knee extensions; <2 min of contractile activity per session) or a control group (CG; n = 16), maintaining daily routines. Before and after the intervention, quadriceps femoris volume, maximal force and power for each leg were assessed, and functional and dual task performance, and cognitive functions were measured.ResultsQuadriceps femoris volume of the more-affected leg increased by 9.4 % in TG. Muscle power of the more-affected, trained (48.2 %), and the less-affected, untrained limb (28.1 %) increased after training. TG showed enhanced balance (8.9 %), gait performance (10.6 %), dual-task performance, executive functions (working memory, verbal fluency tasks), attention, and speed of information processing. CG showed no changes.ConclusionECC-overload flywheel resistance exercise comprising 4 min of contractile activity per week offers a powerful aid to regain muscle mass and function, and functional performance in individuals with stroke. While the current intervention improved cognitive functions, the cause-effect relationship, if any, with the concomitant neuromuscular adaptations remains to be explored.Trial registrationClinical Trials NCT02120846

Effects of Physical Practice and Imagery Practice on Bilateral Transfer in Learning a Sequential Tapping Task.

Recent research on bilateral transfer suggests that imagery training can facilitate the transfer of motor skill from a trained limb to that of an untrained limb above and beyond that of physical practice. To further explore this effect, the present study examined the influence of practice duration and task difficulty on the extent to which imagery training and physical training influences bilateral transfer of a sequential key pressing task. In experiment 1, participants trained on the key pressing task using their non-dominant arm under one of three conditions (physical practice, imagery practice, and no practice). In a subsequent bilateral transfer test, participants performed the sequential task using their untrained dominant arm in either an original order or mirror-ordered sequence. In experiment 2, the same procedures were followed as in experiment 1 except that participants trained with their dominant arm and performed the bilateral transfer task with their non-dominant arm. Results indicated that with extended practice beyond what has been employed in previous studies, physical practice is more effective at facilitating bilateral transfer compared to training with imagery. Interestingly, significant bilateral transfer was only observed for transfer from the non-dominant to the dominant arm with no differences observed between performing the task in an original or mirror ordered sequence. Overall, these findings suggest that imagery training may benefit bilateral transfer primarily at the initial stages of learning, but with extended training, physical practice leads to larger influences on transfer.

Effects of Short-Term Dynamic Constant External Resistance Training and Subsequent Detraining on Strength of the Trained and Untrained Limbs: A Randomized Trial.

Short-term resistance training has been shown to increase isokinetic muscle strength and performance after only two to nine days of training. The purpose of this study was to examine the effects of three days of unilateral dynamic constant external resistance (DCER) training and detraining on the strength of the trained and untrained legs. Nineteen men were randomly assigned to a DCER training group or a non-training control group. Subjects visited the laboratory eight times, the first visit was a familiarization session, the second visit was a pre-training assessment, the subsequent three visits were for training sessions (if assigned to the training group), and the last three visits were post-training assessments 1, 2, and 3 (i.e., 48 h, 1 week, and 2 weeks after the final training session). Strength increased in both trained and untrained limbs from pre- to post-training assessment 1 for the training group and remained elevated at post-training assessments 2 and 3 (p ≤ 0.05). No changes were observed in the control (p > 0.05). Possible strength gains from short-term resistance training have important implications in clinical rehabilitation settings, sports injury prevention, as well as other allied health fields such as physical therapy, occupational therapy, and athletic training.

Mirror Visual Feedback-Induced Performance Improvement and the Influence of Hand Dominance.

Mirror visual feedback (MVF) is a promising technique in clinical settings that can be used to augment performance of an untrained limb. Several studies with healthy volunteers and patients using transcranial magnetic stimulation (TMS) or functional magnetic resonance imaging (fMRI) indicate that functional alterations within primary motor cortex (M1) might be one candidate mechanism that could explain MVF-induced changes in behavior. Until now, most studies have used MVF to improve performance of the non-dominant hand (NDH). The question remains if the behavioral effect of MVF differs according to hand dominance. Here, we conducted a study with two groups of young, healthy right-handed volunteers who performed a complex ball-rotation task while receiving MVF of the dominant (n = 16, group 1, MVFDH) or NDH (n = 16, group 2, MVFNDH). We found no significant differences in baseline performance of the untrained hand between groups before MVF was applied. Furthermore, there was no significant difference in the amount of performance improvement between MVFDH and MVFNDH indicating that the outcome of MVF seems not to be influenced by hand dominance. Thus our findings might have important implications in neurorehabilitation suggesting that patients suffering from unilateral motor impairments might benefit from MVF regardless of the dominance of the affected limb.