Strength-trained adults demonstrate greater corticoreticular activation versus untrained controls.

The rapid increase in strength following strength-training involves neural adaptations, however, their specific localisation remains elusive. Prior focus on corticospinal responses prompts this study to explore the understudied cortical/subcortical adaptations, particularly cortico-reticulospinal tract responses, comparing healthy strength-trained adults to untrained peers. Fifteen chronically strength-trained individuals (≥2 years of training, mean age: 24 ± 7 years) were compared with 11 age-matched untrained participants (mean age: 26 ± 8 years). Assessments included maximal voluntary force (MVF), corticospinal excitability using transcranial magnetic stimulation (TMS), spinal excitability (cervicomedullary stimulation), voluntary activation (VA) and reticulospinal tract (RST) excitability, utilizing StartReact responses and ipsilateral motor-evoked potentials (iMEPs) for the flexor carpi radialis muscle. Trained participants had higher normalized MVF (6.4 ± 1.1 N/kg) than the untrained participants (4.8 ± 1.3 N/kg) (p = .003). Intracortical facilitation was higher in the strength-trained group (156 ± 49%) (p = .02), along with greater VA (98 ± 3.2%) (p = .002). The strength-trained group displayed reduced short-interval-intracortical inhibition (88 ± 8.0%) compared with the untrained group (69 ± 17.5%) (p < .001). Strength-trained individuals exhibited a greater normalized rate of force development (38.8 ± 10.1 N·s-1/kg) (p < .009), greater reticulospinal gain (2.5 ± 1.4) (p = .02) and higher ipsilateral-to-contralateral MEP ratios compared with the untrained group (p = .03). Strength-trained individuals displayed greater excitability within the intrinsic connections of the primary motor cortex and the RST. These results suggest greater synaptic input from the descending cortico-reticulospinal tract to α-motoneurons in strength-trained individuals, thereby contributing to the observed increase in VA and MVF.

Corticospinal and intracortical excitability is modulated in the knee extensors after acute strength training.

The corticospinal responses to high-intensity and low-intensity strength-training of the upper limb are modulated in an intensity-dependent manner. Whether an intensity-dependent threshold occurs following acute strength training of the knee extensors (KE) remains unclear. We assessed the corticospinal responses following high-intensity (85% of maximal strength) or low-intensity (30% of maximal strength) KE strength-training with measures taken during an isometric KE task at baseline, post-5, 30 and 60-min. Twenty-eight volunteers (23 ± 3 years) were randomized to high-intensity (n = 11), low-intensity (n = 10) or to a control group (n = 7). Corticospinal responses were evoked with transcranial magnetic stimulation at intracortical and corticospinal levels. High- or low-intensity KE strength-training had no effect on maximum voluntary contraction force post-exercise (P > 0.05). High-intensity training increased corticospinal excitability (range 130-180%) from 5 to 60 min post-exercise compared to low-intensity training (17-30% increase). Large effect sizes (ES) showed that short-interval cortical inhibition (SICI) was reduced only for the high-intensity training group from 5-60 min post-exercise (24-44% decrease) compared to low-intensity (ES ranges 1-1.3). These findings show a training-intensity threshold is required to adjust CSE and SICI following strength training in the lower limb.

Corticospinal and spinal adaptations to motor skill and resistance training: Potential mechanisms and implications for motor rehabilitation and athletic development.

Optimal strategies for enhancing strength and improving motor skills are vital in athletic performance and clinical rehabilitation. Initial increases in strength and the acquisition of new motor skills have long been attributed to neurological adaptations. However, early increases in strength may be predominantly due to improvements in inter-muscular coordination rather than the force-generating capacity of the muscle. Despite the plethora of research investigating neurological adaptations from motor skill or resistance training in isolation, little effort has been made in consolidating this research to compare motor skill and resistance training adaptations. The findings of this review demonstrated that motor skill and resistance training adaptations show similar short-term mechanisms of adaptations, particularly at a cortical level. Increases in corticospinal excitability and a release in short-interval cortical inhibition occur as a result of the commencement of both resistance and motor skill training. Spinal changes show evidence of task-specific adaptations from the acquired motor skill, with an increase or decrease in spinal reflex excitability, dependant on the motor task. An increase in synaptic efficacy of the reticulospinal projections is likely to be a prominent mechanism for driving strength adaptations at the subcortical level, though more research is needed. Transcranial electric stimulation has been shown to increase corticospinal excitability and augment motor skill adaptations, but limited evidence exists for further enhancing strength adaptations from resistance training. Despite the logistical challenges, future work should compare the longitudinal adaptations between motor skill and resistance training to further optimise exercise programming.

Determining the Intracortical Responses After a Single Session of Aerobic Exercise in Young Healthy Individuals: A Systematic Review and Best Evidence Synthesis.

ABSTRACT: Alibazi, RJ, Pearce, AJ, Rostami, M, Frazer, AK, Brownstein, C, and Kidgell, DJ. Determining the intracortical responses after a single session of aerobic exercise in young healthy individuals: a systematic review and best evidence synthesis. J Strength Cond Res 35(2): 562-575, 2021-A single bout of aerobic exercise (AE) may induce changes in the excitability of the intracortical circuits of the primary motor cortex (M1). Similar to noninvasive brain stimulation techniques, such as transcranial direct current stimulation, AE could be used as a priming technique to facilitate motor learning. This review examined the effect of AE on modulating intracortical excitability and inhibition in human subjects. A systematic review, according to PRISMA guidelines, identified studies by database searching, hand searching, and citation tracking between inception and the last week of February 2020. Methodological quality of included studies was determined using the Downs and Black quality index and Cochrane Collaboration of risk of bias tool. Data were synthesized and analyzed using best-evidence synthesis. There was strong evidence for AE not to change corticospinal excitability and conflicting evidence for increasing intracortical facilitation and reducing silent period and long-interval cortical inhibition. Aerobic exercise did reduce short-interval cortical inhibition, which suggests AE modulates the excitability of the short-latency inhibitory circuits within the M1; however, given the small number of included studies, it remains unclear how AE affects all circuits. In light of the above, AE may have important implications during periods of rehabilitation, whereby priming AE could be used to facilitate motor learning.

Corticomotor correlates of somatosensory reaction time and variability in individuals with post concussion symptoms.

Persistent post concussion symptoms (PPCS) describe the condition when an individual experiences chronic symptoms, particularly fatigue, beyond the expected time of recovery. The aim of this study was to quantify the effect of fatigue and related ongoing symptoms on somatosensory and corticomotor pathways using reaction time (RT) testing, and single-pulse and paired-pulse transcranial magnetic stimulation (TMS). Eighty-three participants (nine female, mean age 37.9 ± 11.5 years) were divided into two groups (persistent symptoms versus asymptomatic) following self-report based upon previously published clinical symptom scores. All participants completed somatosensory and visuomotor RT testing, as well as corticomotor excitability and inhibition measurements via TMS. Participants in the persistent symptom group (n = 38) reported greater number of previous concussions (t = 2.81, p = 0.006) and significantly higher levels of fatigue and related symptoms in the asymptomatic group (n = 45; t = 11.32, p < 0.006). Somatosensory RT showed significant slowing and increased variability in the persistent symptoms group (p < 0.001), however no significant differences were observed between groups for visuomotor RTs. Transcranial magnetic stimulation revealed differences between groups for intracortical inhibition at all stimulus intensities and paired pulse measures. The results indicate that somatosensory and corticomotor systems reflect on-going fatigue. From a practical perspective, objective and simplistic measures such as somatosensory and corticomotor measures can be used in the assessment of PPCS and gauging the efficacy of post concussion rehabilitation programmes.

Tracking the corticospinal responses to strength training.

PURPOSE: The motor cortex (M1) appears to be a primary site of adaptation following both a single session, and repeated strength-training sessions across multiple weeks. Given that a single session of strength-training is sufficient to induce modification at the level of the M1 and corticospinal tract, this study sought to determine how these acute changes in M1 and corticospinal tract might accumulate across the course of a 2-week heavy-load strength-training program. METHODS: Transcranial magnetic stimulation (TMS) was used to infer corticospinal excitability (CSE), intracortical facilitation (ICF), short and long-interval intracortical inhibition (SICI and LICI) and silent period duration prior to and following each training session during a 2-week heavy-load strength-training period. RESULTS: Following 2-weeks of strength-training, increases in strength (15.5%, P = 0.01) were accompanied by an increase in CSE (44%, P = 0.006) and reductions in both silent period duration (14%, P < 0.0001) and SICI (35%, P = 0.0004). Early training sessions acutely increased CSE and ICF, and acutely reduced silent period duration and SICI. However, later training sessions failed to modulate SICI and ICF, with substantial adaptations occurring offline between training sessions. No acute or retained changes in LICI were observed. Co-contraction of antagonists reduced by 36% following 2-weeks of strength-training. CONCLUSIONS: Collectively, these results indicate that corticospinal plasticity occurs within and between training sessions throughout a training period in distinct early and later stages that are modulated by separate mechanisms of plasticity. The development of strength is akin to the previously reported changes that occur following motor skill training.

Modulation of intracortical inhibition and excitation in agonist and antagonist muscles following acute strength training.

PURPOSE: Transcranial magnetic stimulation (TMS) usually investigates the corticospinal responses of the agonist muscle to strength training, despite the role of the antagonist muscle in strength development. We examined the intracortical responses from an agonist and antagonist muscle following a single session of heavy-loaded strength training (dominant-arm only) to identify the early antagonistic responses to a single session that may accompany improvements in strength. METHODS: Corticospinal and motor cortical excitability and inhibition was collected from agonist and antagonist muscles prior to and following a single session of heavy-loaded wrist flexor training in 18 individuals. Training consisted of four sets 6-8 repetitions at 80% of 1-repetition maximum (1-RM). Recruitment curves for corticospinal excitability and inhibition of the right wrist flexor and wrist extensor muscles were constructed and assessed by examining the area under the recruitment curve. Intracortical measures were obtained using paired-pulse TMS. RESULTS: Following a single training session, increases in corticospinal excitability were observed in both the agonist and antagonist muscles. This was accompanied by decreases in corticospinal inhibition in both muscles. Intracortical inhibition was reduced and intracortical facilitation was increased for the agonist muscle only. Intracortical measures in the antagonist muscle remained unchanged after training. CONCLUSIONS: These findings indicate that the corticospinal responses to a single session of strength training are similar between agonist and antagonist muscles, but the intrinsic cortico-cortical circuitry of the antagonist remains unchanged. The corticospinal responses are likely due to increased involvement/co-activation of the antagonist muscle during training as the agonist muscle fatigues.

Priming the Motor Cortex With Anodal Transcranial Direct Current Stimulation Affects the Acute Inhibitory Corticospinal Responses to Strength Training.

Frazer, AK, Howatson, G, Ahtiainen, JP, Avela, J, Rantalainen, T, and Kidgell, DJ. Priming the motor cortex with anodal transcranial direct current stimulation affects the acute inhibitory corticospinal responses to strength training. J Strength Cond Res 33(2): 307-317, 2019-Synaptic plasticity in the motor cortex (M1) is associated with strength training (ST) and can be modified by transcranial direct current stimulation (tDCS). The M1 responses to ST increase when anodal tDCS is applied during training due to gating. An additional approach to improve the M1 responses to ST, which has not been explored, is to use anodal tDCS to prime the M1 before a bout of ST. We examined the priming effects of anodal tDCS of M1 on the acute corticospinal responses to ST. In a randomized double-blinded cross-over design, changes in isometric strength, corticospinal excitability, and inhibition (assessed as area under the recruitment curve [AURC] using transcranial magnetic stimulation) were analyzed in 13 adults exposed to 20 minutes of anodal tDCS and sham tDCS followed by a ST session of the right elbow flexors. We observed a significant decrease in isometric elbow-flexor strength immediately after training (11-12%; p < 0.05), which was not different between anodal tDCS and sham tDCS. Transcranial magnetic stimulation revealed a 24% increase in AURC for corticospinal excitability after anodal tDCS and ST; this increase was not different between conditions. However, there was a 14% reduction in AURC for corticospinal inhibition when anodal tDCS was applied before ST when compared with sham tDCS and ST (all p < 0.05). Priming anodal tDCS had a limited effect in facilitating corticospinal excitability after an acute bout of ST. Interestingly, the interaction of anodal tDCS and ST seems to affect the excitability of intracortical inhibitory circuits of the M1 through nonhomeostatic mechanisms.

Determining the Corticospinal Responses to Single Bouts of Skill and Strength Training.

Mason, J, Frazer, AK, Jaberzadeh, S, Ahtiainen, JP, Avela, J, Rantalainen, T, Leung, M, and Kidgell, DJ. Determining the corticospinal responses to single bouts of skill and strength training. J Strength Cond Res 33(9): 2299-2307, 2019-Neuroplastic changes in the primary motor cortex accompany performance improvements following motor practice. Recent evidence suggests that the corticospinal responses to strength and skill training are similar, following both a single session and repeated bouts of training, promoting discussion that strength training is a form of motor learning. However, these findings are limited by the lack of a light-load strength training group. Therefore, the aim of the current study was to determine whether a single session of heavy-load strength training, light-load strength training or skill training differentially modulates the corticospinal pathway. Transcranial magnetic stimulation was used to assess the excitatory and inhibitory circuitry of the motor cortex following a single session of skill training, and following a single session of light-load and heavy-load strength training. Following a single session of training, participants in all groups experienced comparable increases in corticospinal excitability (ranging from 38 to 46%, all p < 0.05); however, disparity was observed in the inhibitory responses. Corticospinal inhibition was reduced in all 3 single-sessions, although to a greater magnitude in the heavy-load and skill-training sessions (22 and 18% respectively, compared with 11% following light-load training, all p < 0.05). Short-interval intracortical inhibition was reduced immediately following single sessions of heavy-load strength training (40% p < 0.05) and skill training (47% p < 0.05), but remained unchanged the following light-load strength training session. It appears that the corticospinal responses to single sessions of different types of strength and skill training are task-dependent. These findings reinforce the notion that strength training, at least when heavily-loaded, can be considered a form of motor learning, potentially because of the sensory feedback involved.

Determining the potential sites of neural adaptation to cross-education: implications for the cross-education of muscle strength.

Cross-education describes the strength gain in the opposite, untrained limb following a unilateral strength training program. Since its discovery in 1894, several studies now confirm the existence of cross-education in contexts that involve voluntary dynamic contractions, eccentric contraction, electrical stimulation, whole-body vibration and, more recently, following mirror feedback training. Although many aspects of cross-education have been established, the mediating neural mechanisms remain unclear. Overall, the findings of this review show that the neural adaptations to cross-education of muscle strength most likely represent a continuum of change within the central nervous system that involves both structural and functional changes within cortical motor and non-motor regions. Such changes are likely to be the result of more subtle changes along the entire neuroaxis which include, increased corticospinal excitability, reduced cortical inhibition, reduced interhemispheric inhibition, changes in voluntary activation and new regions of cortical activation. However, there is a need to widen the breadth of research by employing several neurophysiological techniques (together) to better understand the potential mechanisms mediating cross-education. This fundamental step is required in order to better prescribe targeted and effective guidelines for the clinical practice of cross-education. There is a need to determine whether similar cortical responses also occur in clinical populations where, perhaps, the benefits of cross-education could be best observed.

Corticospinal responses following strength training: a systematic review and meta-analysis.

Strength training results in changes in skeletal muscle; however, changes in the central nervous system also occur. Over the last 15 years, non-invasive brain stimulation techniques, such as transcranial magnetic stimulation, have been used to study the neural adaptations to strength training. This review explored the hypothesis that the neural adaptations to strength training may be due to changes in corticospinal excitability and inhibition and, such changes, contribute to the gain in strength following strength training. A systematic review, according to PRISMA guidelines, identified studies by database searching, hand-searching and citation tracking between January 1990 and the first week of February 2017. Methodological quality of included studies was determined using the Downs and Black quality index. Data were synthesised and interpreted from meta-analysis. Nineteen studies investigating the corticospinal responses following strength training were included. Meta-analysis found that strength training increased strength [standardised mean difference (SMD) 0.84, 95% CI 0.55 to 1.13], decreased short-interval intracortical inhibition (SMD -1.00, 95% CI -1.84 to -0.17) and decreased the cortical silent period (SMD -0.66, 95% CI -1.00 to -0.32). Strength training had no effect on motor threshold (SMD -0.12, 95% CI -0.49 to 0.25), but a borderline effect for increased corticospinal excitability (SMD 0.27, 95% CI 0.00 to 0.54). In untrained healthy participants, the corticospinal response to strength training is characterised by reduced intracortical inhibition and cortical silent period duration, rather than changes in corticospinal excitability. These data demonstrate that strength training targets intracortical inhibitory networks within the primary motor cortex (M1) and corticospinal pathway, characterising an important neural adaptation to strength training.

Cross-education of muscular strength is facilitated by homeostatic plasticity.

PURPOSE: We examined the effect of priming the ipsilateral motor cortex (M1) using anodal transcranial direct current stimulation (tDCS) prior to a single bout of strength training on the cross-transfer of strength and corticospinal excitability and inhibition of the ipsilateral M1. METHODS: In a randomized double-blinded cross-over design, changes in strength and indices of corticospinal plasticity were analysed in 13 adults who were exposed to 20 min of ipsilateral anodal and sham tDCS (applied to the ipsilateral M1 to the training arm) followed by a single strength training session of the right Biceps Brachii only. RESULTS: The induction of homeostatic plasticity via anodal tDCS priming, significantly increased strength of the untrained left Biceps Brachii (12%) compared to sham tDCS (2%), increased corticospinal excitability (12-33%) and cross-activation (25%) when ipsilateral anodal tDCS was applied to the right M1 prior to a single session of strength training. Interestingly, ipsilateral sham tDCS and strength training resulted in an average increase in MEP amplitude of 2-32%. CONCLUSION: The novel findings of this study include: priming the ipsilateral M1 via anodal tDCS prior to a single bout of strength training augments the cross-transfer of strength which is manifested by an increase in corticospinal excitability and cross-activation. These findings provide insight into how priming methods that induce homeostatic plasticity may be used to enhance the cross-education phenomenon.

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

PURPOSE: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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.

Differential modulation of corticomotor excitability in older compared to young adults following a single bout of strength -exercise.

Evidence shows corticomotor plasticity diminishes with age. Nevertheless, whether strength-training, a proven intervention that induces corticomotor plasticity in younger adults, also takes effect in older adults, remains untested. This study examined the effect of a single-session of strength-exercise on corticomotor plasticity in older and younger adults. Thirteen older adults (72.3 ± 6.5 years) and eleven younger adults (29.9 ± 6.9 years), novice to strength-exercise, participated. Strength-exercise involved four sets of 6-8 repetitions of a dumbbell biceps curl at 70-75% of their one-repetition maximum (1-RM). Muscle strength, cortical, corticomotor and spinal excitability, before and up to 60-minutes after the strength-exercise session were assessed. We observed significant changes over time (p < 0.05) and an interaction between time and age group (p < 0.05) indicating a decrease in corticomotor excitability (18% p < 0.05) for older adults at 30- and 60-minutes post strength-exercise and an increase (26% and 40%, all p < 0.05) in younger adults at the same time points. Voluntary activation (VA) declined in older adults immediately post and 60-minutes post strength-exercise (36% and 25%, all p < 0.05). Exercise had no effect on the cortical silent period (cSP) in older adults however, in young adults cSP durations were shorter at both 30- and 60- minute time points (17% 30-minute post and 9% 60-minute post, p < 0.05). There were no differences in short-interval cortical inhibition (SICI) or intracortical facilitation (ICF) between groups. Although the corticomotor responses to strength-exercise were different within groups, overall, the neural responses seem to be independent of age.

Induction of cortical plasticity and improved motor performance following unilateral and bilateral transcranial direct current stimulation of the primary motor cortex.

BACKGROUND: Transcranial direct current stimulation (tDCS) is a non-invasive technique that modulates the excitability of neurons within the primary motor cortex (M1). Research shows that anodal-tDCS applied over the non-dominant M1 (i.e. unilateral stimulation) improves motor function of the non-dominant hand. Similarly, previous studies also show that applying cathodal tDCS over the dominant M1 improves motor function of the non-dominant hand, presumably by reducing interhemispheric inhibition. In the present study, one condition involved anodal-tDCS over the non-dominant M1 (unilateral stimulation) whilst a second condition involved applying cathodal-tDCS over the dominant M1 and anodal-tDCS over non-dominant M1 (bilateral stimulation) to determine if unilateral or bilateral stimulation differentially modulates motor function of the non-dominant hand. Using a randomized, cross-over design, 11 right-handed participants underwent three stimulation conditions: 1) unilateral stimulation, that involved anodal-tDCS applied over the non-dominant M1, 2) bilateral stimulation, whereby anodal-tDCS was applied over the non-dominant M1, and cathodal-tDCS over the dominant M1, and 3) sham stimulation. Transcranial magnetic stimulation (TMS) was performed before, immediately after, 30 and 60 minutes after stimulation to elucidate the neural mechanisms underlying any potential after-effects on motor performance. Motor function was evaluated by the Purdue pegboard test. RESULTS: There were significant improvements in motor function following unilateral and bilateral stimulation when compared to sham stimulation at all-time points (all P < 0.05); however there was no difference across time points between unilateral and bilateral stimulation. There was also a similar significant increase in corticomotor excitability with both unilateral and bilateral stimulation immediately post, 30 minutes and 60 minutes compared to sham stimulation (all P < 0.05). Unilateral and bilateral stimulation reduced short-interval intracortical inhibition (SICI) immediately post and at 30 minutes (all P < 0.05), but returned to baseline in both conditions at 60 minutes. There was no difference between unilateral and bilateral stimulation for SICI (P > 0.05). Furthermore, changes in corticomotor plasticity were not related to changes in motor performance. CONCLUSION: These results indicate that tDCS induced behavioural changes in the non-dominant hand as a consequence of mechanisms associated with use-dependant cortical plasticity that is independent of the electrode arrangement.

Evidence of altered corticomotor inhibition in older adults with a history of repetitive neurotrauma. A transcranial magnetic stimulation study.

International concern continues regarding the association between the long-term neurophysiologic changes from repetitive neurotrauma associated with contact and collision sports. This study describes corticomotor changes in retired contact/collision sport athletes and controls, between the ages of 30 and 70 years. Retired athletes (n = 152; 49.1 ± 8.5 years) and controls (n = 72; 47.8 ± 9.5 years) were assessed using single and paired-pulse transcranial magnetic stimulation (TMS) for active motor threshold (aMT), motor evoked potential and cortical silent period duration (expressed as MEP:cSP ratio), and short- and long-interval intracortical inhibition (SICI and LICI). Motor threshold, MEP:cSP, SICI and LICI for both groups were correlated across age. Controls showed significant moderate correlations for MEP:cSP ratios at 130% (rho = 0.48, p < 0.001), 150% (rho = 0.49, p < 0.001) and 170% aMT (rho = 0.42; p < 0.001) and significant small negative correlation for SICI (rho = -0.27; p = 0.030), and moderate negative correlation for LICI (rho = -0.43; p < 0.001). Group-wise correlation analysis comparisons showed significant correlation differences between groups for 130% (p = 0.016) and 150% aMT (p = 0.009), specifically showing retired athletes were displaying increased corticomotor inhibition. While previous studies have focussed studies on older athletes (>50 years), this study is the first to characterize corticomotor differences between retired athletes and controls across the lifespan. These results, demonstrating pathophysiological differences in retired athletes across the lifespan, provide a foundation to utilise evoked potentials as a prodromal marker in supplementing neurological assessment for traumatic encephalopathy syndrome associated with contact/collision sport athletes that is currently lacking physiological biomarkers.

Identifying the role of the reticulospinal tract for strength and motor recovery: A scoping review of nonhuman and human studies.

In addition to the established postural control role of the reticulospinal tract (RST), there has been an increasing interest on its involvement in strength, motor recovery, and other gross motor functions. However, there are no reviews that have systematically assessed the overall motor function of the RST. Therefore, we aimed to determine the role of the RST underpinning motor function and recovery. We performed a literature search using Ovid Medline, Embase, CINAHL Plus, and Scopus to retrieve papers using key words for RST, strength, and motor recovery. Human and animal studies which assessed the role of RST were included. Studies were screened and 32 eligible studies were included for the final analysis. Of these, 21 of them were human studies while the remaining were on monkeys and rats. Seven experimental animal studies and four human studies provided evidence for the involvement of the RST in motor recovery, while two experimental animal studies and eight human studies provided evidence for strength gain. The RST influenced gross motor function in two experimental animal studies and five human studies. Overall, the RST has an important role for motor recovery, gross motor function and at least in part, underpins strength gain. The role of RST for strength gain in healthy people and its involvement in spasticity in a clinical population has been limitedly described. Further studies are required to ascertain the role of the RST's role in enhancing strength and its contribution to the development of spasticity.

Unilateral Strength Training Imparts a Cross-Education Effect in Unilateral Knee Osteoarthritis Patients.

Background: Worldwide, 86 million individuals over the age of 20 were diagnosed with knee osteoarthritis (KOA) in 2020. Hallmark features of KOA are the loss in knee extensor strength, increasing knee pain severity, and deficits in functional performance. There is a critical need for the investigation into potential cost-effective therapeutic interventions in the treatment of KOA. A potential therapeutic option is the cross-education phenomenon. Methods: This was a non-blinded randomized control trial, with a 4-week intervention, with a pre, post and follow-up assessment (3 months post intervention). Outcome measures of isometric knee extensor strength, rectus femoris muscle thickness and neuromuscular activation were assessed at all-time points. Results: Compared to age-matched KOA controls, 4 weeks of unilateral strength training in end-stage KOA patients increased strength of the untrained affected KOA limb by 20% (p < 0.05) and reduced bilateral hamstring co-activation in the KOA intervention group compared to the KOA control group (p < 0.05). Conclusions: A 4-week-long knee extensor strength training intervention of the contralateral limb in a cohort with diagnosed unilateral KOA resulted in significant improvements to knee extensor strength and improved neuromuscular function of the KOA limb. Importantly, these results were maintained for 3 months following the intervention.

Assessment of Somatosensory and Motor Processing Time in Retired Athletes with a History of Repeated Head Trauma.

Measurement of the adverse outcomes of repeated head trauma in athletes is often achieved using tests where the comparator is 'accuracy'. While it is expected that ex-athletes would perform worse than controls, previous studies have shown inconsistent results. Here we have attempted to address these inconsistencies from a different perspective by quantifying not only accuracy, but also motor response times. Age-matched control subjects who have never experienced head trauma (n = 20; 41.8 ± 14.4 years) where compared to two cohorts of retired contact sport athletes with a history of head trauma/concussions; one with self-reported concerns (n = 36; 45.4 ± 12.6 years), and another with no ongoing concerns (n = 19; 43.1 ± 13.5 years). Participants performed cognitive (Cogstate) and somatosensory (Cortical Metrics) testing with accuracy and motor times recorded. Transcranial magnetic stimulation (TMS) investigated corticospinal conduction and excitability. Results showed that there was little difference between groups in accuracy scores. Conversely, motor times in all but one test revealed that ex-athletes with self-reported concerns were significantly slower compared to other groups (p ranges 0.031 to <0.001). TMS latency showed significantly increased time (p = 0.008) in the group with ongoing concerns. These findings suggest that incorporating motor times is more informative than considering accuracy scores alone.

Determining the Corticospinal Responses and Cross-Transfer of Ballistic Motor Performance in Young and Older Adults: A Systematic Review and Meta-Analysis.

Ballistic motor training induces plasticity changes and imparts a cross-transfer effect. However, whether there are age-related differences in these changes remain unclear. Thus, the purpose of this study was to perform a meta-analysis to determine the corticospinal responses and cross-transfer of motor performance following ballistic motor training in young and older adults. Meta-analysis was performed using a random-effects model. A best evidence synthesis was performed for variables that had insufficient data for meta-analysis. There was strong evidence to suggest that young participants exhibited greater cross-transfer of ballistic motor performance than their older counterparts. This meta-analysis showed no significant age-related differences in motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and surface electromyography (sEMG) for both hands following ballistic motor training.