Adaptations in corticospinal excitability and inhibition are not spatially confined to the agonist muscle following strength training

Purpose: We used transcranial magnetic stimulation (TMS) to determine the corticospinal responses from an agonist and synergist muscle following strength training of the right elbow flexors. Methods: Motor evoked potentials were recorded from the 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 and control group; n = 10) before and after three weeks of strength training at 80% of 1-repetition maximum (1-RM). To characterise the input-output properties of the corticospinal tract, stimulus-response curves for corticospinal excitability and inhibition of the right Biceps Brachii and Flexor Carpi Radialis were constructed and assessed by examining the area under the recruitment curve (AURC). Results: Strength training resulted in a 29% (P < 0.001) increase in 1-RM Biceps Brachii strength and this was accompanied by a 19% increase in isometric strength of the wrist flexors (P = 0.001). TMS revealed an increase in corticospinal excitability AURC and a decrease in silent period duration AURC for the Biceps Brachii and Flexor Carpi Radialis following strength training (all P < 0.05). However, the changes in corticospinal function were not associated with increased muscle strength. Conclusion: These findings show that the corticospinal responses to strength training of a proximal upper limb muscle is not spatially restricted, but rather, results in a change in connectivity, among an agonist and a synergistic muscle relevant to force production

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

Central & peripheral fatigue in male cyclists after 4, 20 & 40 km time-trials

Purpose: Few studies have assessed neuromuscular fatigue after self-paced locomotor exercise; moreover, none have assessed the degree of supraspinal fatigue. This study assessed central and peripheral fatigue after self-paced exercise of different durations. Methods: Thirteen well-trained male cyclists completed 4 km, 20 km and 40 km simulated time-trials (TTs). Pre- and immediately post-TT (30 min)

Neuromuscular changes and the rapid adaptation following a bout of damaging eccentric exercise

An initial bout of eccentric exercise is known to protect against muscle damage following a repeated bout of the same exercise, however, the neuromuscular adaptions owing to this phenomenon are unknown. Aim: To determine if neuromuscular disturbances are modulated following a repeated bout of eccentric exercise. Methods: Following eccentric exercise performed with the elbow-flexors, we measured maximal voluntary force, resting twitch force, muscle soreness, creatine kinase and voluntary activation using motor point and motor cortex stimulation at baseline, immediately post and at 1, 2, 3, 4 and 7 days post-exercise on two occasions, separated by 3 weeks. Results: Significant muscle damage and fatigue was evident following the first exercise bout; maximal voluntary contraction was reduced immediately by 32% and remained depressed at 7 days post-exercise. Soreness and creatine kinase release peaked at 3 and 4 days post-exercise, respectively. Resting twitch force remained significantly reduced at 7 days (−48%) whilst voluntary activation measured with motor point and motor cortex stimulation was reduced until 2 and 3 days, respectively. A repeated bout effect was observed with attenuated soreness and creatine kinase release and a quicker recovery of maximal voluntary contraction and resting twitch force. A similar decrement in voluntary activation was observed following both bouts; however, following the repeated bout there was a significantly smaller reduction in, and a faster recovery of voluntary activation measured using motor cortical stimulation. Conclusion: Our data suggest that the repeated bout effect may be explained, partly, by a modification in motor corticospinal drive

Determining the Sites of Neural Adaptations to Resistance Training: A Systematic Review and Meta-Analysis

Background: Resistance-training causes changes in the central nervous system (CNS); however, the sites of these adaptations remain unclear. Objective: To determine sites of neural adaptation to resistance-training by conducting a systematic review and meta-analysis on the cortical and subcortical responses to resistance-training. Methods: Evidence from randomized controlled trials (RCTs) that focused on neural adaptations to resistance-training was pooled to assess effect estimates for changes in strength, cortical, and subcortical adaptations. Results: The magnitude of strength gain in 30 RCTs (n = 623) reported a standardised mean difference (SMD) of 0.67 (95% CI 0.41, 0.94; P < 0.001) that measured at least one cortical/subcortical neural adaptation which included: motor-evoked potentials (MEP; 19 studies); silent period (SP; 7 studies); short-interval intracortical inhibition (SICI; 7 studies); cervicomedullary evoked potentials (CMEP; 1 study); transcranial magnetic stimulation voluntary activation (VATMS; 2 studies); H-reflex (10 studies); and V-wave amplitudes (5 studies). The MEP amplitude during voluntary contraction was greater following resistance-training (SMD 0.55; 95% CI 0.27, 0.84; P < 0.001, n = 271), but remained unchanged during rest (SMD 0.49; 95% CI -0.68, 1.66; P = 0.41, n = 114). Both SP (SMD 0.65; 95% CI 0.29, 1.01; P < 0.001, n = 184) and active SICI (SMD 0.68; 95% CI 0.14, 1.23; P = 0.01, n = 102) decreased, but resting SICI remained unchanged (SMD 0.26; 95% CI − 0.29, 0.81; P = 0.35, n = 52). Resistance-training improved neural drive as measured by V-wave amplitude (SMD 0.62; 95% CI 0.14, 1.10; P = 0.01, n = 101), but H-reflex at rest (SMD 0.16; 95% CI − 0.36, 0.68; P = 0.56; n = 57), during contraction (SMD 0.15; 95% CI − 0.18, 0.48; P = 0.38, n = 142) and VATMS (MD 1.41; 95% CI − 4.37, 7.20; P = 0.63, n = 44) remained unchanged. Conclusion: There are subtle neural adaptations following resistance-training involving both cortical and subcortical adaptations that act to increase motoneurone activation and likely contribute to the training-related increase in muscle strength

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

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

Repeatability of Corticospinal and Spinal Measures during Lengthening and Shortening Contractions in the Human Tibialis Anterior Muscle

Elements of the human central nervous system (CNS) constantly oscillate. In addition, there are also methodological factors and changes in muscle mechanics during dynamic muscle contractions that threaten the stability and consistency of transcranial magnetic stimulation (TMS) and perpherial nerve stimulation (PNS) measures

Bilateral renal agenesis/hypoplasia/dysplasia (BRAHD):postmortem analysis of 45 cases with breakpoint mapping of two de novo translocations

Bilateral renal agenesis/hypoplasia/dysplasia (BRAHD) is a relatively common, lethal malformation in humans. Established clinical risk factors include maternal insulin dependent diabetes mellitus and male sex of the fetus. In the majority of cases, no specific etiology can be established, although teratogenic, syndromal and single gene causes can be assigned to some cases.45 unrelated fetuses, stillbirths or infants with lethal BRAHD were ascertained through a single regional paediatric pathology service (male:female 34:11 or 3.1:1). The previously reported phenotypic overlaps with VACTERL, caudal dysgenesis, hemifacial microsomia and Müllerian defects were confirmed. A new finding is that 16/45 (35.6%; m:f 13:3 or 4.3:1) BRAHD cases had one or more extrarenal malformations indicative of a disoder of laterality determination including; incomplete lobulation of right lung (seven cases), malrotation of the gut (seven cases) and persistence of the left superior vena cava (five cases). One such case with multiple laterality defects and sirelomelia was found to have a de novo apparently balanced reciprocal translocation 46,XY,t(2;6)(p22.3;q12). Translocation breakpoint mapping was performed by interphase fluorescent in-situ hybridization (FISH) using nuclei extracted from archival tissue sections in both this case and an isolated bilateral renal agenesis case associated with a de novo 46,XY,t(1;2)(q41;p25.3). Both t(2;6) breakpoints mapped to gene-free regions with no strong evidence of cis-regulatory potential. Ten genes localized within 500 kb of the t(1;2) breakpoints. Wholemount in-situ expression analyses of the mouse orthologs of these genes in embryonic mouse kidneys showed strong expression of Esrrg, encoding a nuclear steroid hormone receptor. Immunohistochemical analysis showed that Esrrg was restricted to proximal ductal tissue within the embryonic kidney.The previously unreported association of BRAHD with laterality defects suggests that renal agenesis may share a common etiology with heterotaxy in some cases. Translocation breakpoint mapping identified ESRRG as a plausible candidate gene for BRAHD