ECSS Paris 2023: OP-BM01
INTRODUCTION: Neural determinants of cross-education during submaximal contractions have been associated with increased common input to spinal motoneurons and enhanced motor unit (MU) recruitment, without changes in spinal motoneuron drive [1]. However, the characterisation of MU behaviour during maximal voluntary contractions (MVCs) is generally unfeasible in surface EMG studies, due to limitations in decomposing the full population of active MUs [2]. Therefore, we adopted a novel approach to decompose MU activity across multiple MVCs (up to four), each including a 5-s hold phase. This approach increases the number of independent sources available to the decomposition algorithm, enabling more accurate MU identification [3] and obtaining a relatively large sample of MUs (> 6 per participant). METHODS: High-density surface EMG was recorded from the biceps brachii in the trained (TL) and contralateral untrained limb (UL) during MVCs to assess maximal voluntary force (MVF) and MU properties. Ten participants (BMI: 21.8 ± 2.5 kg∙m-2) completed a 4-week unilateral strength training program (4x6 repetitions at 80% MVF; 3 sessions/week) and were compared with a control group (n=10, BMI: 23.1 ± 4.8 kg∙m-2). Analyses were performed on longitudinally tracked MUs over the intervention. The strength of the neural drive was estimated as the mean discharge rate (DR) of the MU pool. Cumulative MU recruitment and spiking activity were also assessed with EMG amplitude and muscle fibre conduction velocity (MFCV) [4]. RESULTS: Training produced significant MVF increases in the TL (+14 %, p<0.001) and UL (+6 %, p=0.004). These gains were accompanied by increased MU-DR (TL, +4.89 pps, p<0.001; UL,+2.19, p=0.001) and concurrent increases in EMG amplitude (TL, +281 μV; UL,+195 μV) and MFCV (TL, +0.43 m∙s-1; UL,+0.35 m∙s-1), suggesting greater cumulative neural activity and activation of larger MUs. Higher MFCV does not necessarily indicate increased muscle cross-sectional area, but rather a higher proportion of larger muscle fibres activated by the central nervous system. No changes were observed in the control group in any parameter (p>0.05). CONCLUSION: This study provides the first in vivo evidence that unilateral strength training increases spinal motoneuron output to untrained muscles during MVCs. These findings extend previous observations from submaximal contractions by demonstrating that cross-transfer of maximal force is mediated by a higher MU-DR rather than by MU recruitment alone [1]. These results also indicate that cross-education relies on distinct neural mechanisms at submaximal vs maximal force output, plausibly reflecting differences in supraspinal drive during maximal-effort contractions [5]. References 1. https://doi.org/10.1113/jp288954 2. https://doi.org/10.1016/j.jelekin.2020.102426 3. https://doi.org/10.1088/1741-2560/11/1/016008 4. https://doi.org/10.1152/japplphysiol.00810.2024 5. https://doi.org/10.1523/JNEUROSCI.0627-21.2022
Read CV Edoardo LecceECSS Paris 2023: OP-BM01
INTRODUCTION: Combat sports, such as boxing, consistently report some of the highest concussion rates per 100,000 athletic events. Despite this, limited research has examined the cumulative head impacts sustained during training, or the acute neurophysiological responses to a single sparring session. Using instrumented mouthguards (IMG), transcranial magnetic stimulation (TMS), and peripheral nerve stimulation (PNS), this naturalistic observational study examined acute changes in corticospinal and peripheral neuromuscular function following combat sport sparring. METHODS: 13 male competitive amateur combat sports athletes (age: 23 ± 5yrs, stature: 175 ± 8cm, BM: 74 ± 17kg) completed TMS & PNS testing before, immediately, and 48h after a single sparring session. In addition, five athletes from this cohort (age: 25 ± 6yrs, stature: 180 ± 11cm, BM: 83 ± 26kg) wore IMGs and were monitored before and immediately after multiple sessions. Outcome measures included Active Motor Threshold (AMT), Maximal Voluntary Contraction (MVC), Compound Muscle Action Potential (MMAX), Motor Evoked Potential (MEP), and Cortical Silent Period (cSP). RESULTS: Participants took part in 15 ± 2 min of sparring (min: 8 min, max: 20 min) and sustained a median head impact frequency (HIF) of 19 (IQR: 36) in a single session. The highest peak linear acceleration (PLA) and peak angular acceleration (PAA) recorded were 50 g and 5775 rad/s², respectively. Mean PLA per impact was 12 ± 6 g, while mean PAA was 1048 ± 622 rad/s². Cumulative load (sum of all impact load) per session totalled 240 ± 136 g for PLA (CLA) and 20,421 ± 11,910 rad/s² for PAA (CAA). AMT increased post-sparring (p = .024 ) while MMAX decreased immediately post (p = .031; .018) but returned to baseline by 48 hours. MEP amplitude decreased post (p < .001) and remained suppressed at 48 hours (p = .034), while cSP duration increased post-sparring (p = .044) and did not return to baseline at 48 hours. Significant positive repeated measures correlations (p < .001) were observed between cSP duration and HIF (r = 0.69), CLA (r = 0.89), and CAA (r = 0.91). In addition, a linear mixed model demonstrated that HIF (β = 1.27), CLA (β = 0.91), and CAA (β = 1.08) were significant predictors (p < .001) of cSP change after accounting for participant-level variability. CONCLUSION: These findings provide novel evidence that a typical combat sport sparring session can result in suppressed MEP amplitude, prolonged cSP, and elevated motor threshold, suggesting transient neurophysiological disruption following repeated head impacts after a single session. Furthermore, head impact characteristics, particularly CAA, are strongly associated with the observed transient GABAB-mediated inhibitory upregulation post-impact. Mechanistically, these findings reinforce rotational acceleration as a primary driver of acute neurophysiological disturbance following head impacts, likely reflecting load-dependent modulation of cortical inhibitory circuitry in response to repeated head impacts.
Read CV Nasir UddinECSS Paris 2023: OP-BM01
INTRODUCTION: Yips is defined as a psycho-neuromuscular impairment that disrupts the execution of fine motor skills in sports performance [1]. Yips can cause severe deterioration in sports performance and even lead to an athlete’s career termination; however, its underlying neural mechanisms remain unclear. Among the brain regions involved, the primary motor cortex (M1) deserves particular attention due to its critical role in the output of descending motor commands. Indeed, a previous study indicated that athletes with the yips exhibit greater activation in the M1 than healthy controls during motor execution [2]. This study aimed to elucidate the causal effects of inhibitory continuous theta burst stimulation (cTBS) over the M1 on the occurrence of the yips and throwing performance in baseball players with the yips. METHODS: 12 male baseball players (age: 22.5 ± 3.3 years; playing experience: 13.9 ± 3.6 years) with yips symptoms participated. Participants performed a throwing task toward a target located 18.44 m away at a self-selected subjective intensity at which they experienced the most pronounced yips symptoms (approximately 50–80% of maximal effort). They first performed a pre-stimulation throwing set (pre), followed by two throwing sets (post1, post2), each preceded by cTBS [3]. Each set consisted of 20 throwing trials. cTBS was applied over the forearm hotspot in the M1 contralateral to the dominant pitching hand. Throwing performance measures included ball speed, proportion of throws with self-reported yips symptoms, and absolute error of ball arrival position. The Friedman tests and Wilcoxon signed-rank tests were used to compare these measures across conditions, with statistical significance set at p < 0.05. RESULTS: The Friedman test revealed no significant differences in ball speed among all conditions (p > 0.05). In contrast, a Friedman test followed by post-hoc Wilcoxon signed-rank tests showed that both the post1 and post2 conditions exhibited significantly lower rates of throws with self-reported yips symptoms (pre: median [IQR]: 25.0 % [12.5–41.2 %]; post1: 15.0 % [3.8–25.0 %]; post2: 5.0 % [0–11.2 %]) and lower absolute error of ball arrival position (pre: median [IQR]: 58.6 cm [52.4–76.4 cm]; post1: 56.7 cm [42.9–74.3 cm]; post2: 52.5 cm [38.9–59.9 cm] ) compared with the pre condition (post1: p < 0.05; post2: p < 0.01). CONCLUSION: Our results showed that cTBS significantly reduced the rate of throws with self-reported yips symptoms and the absolute error of ball arrival position, whereas ball speed remained unchanged. These findings indicate that the observed changes cannot be attributed to differences in throwing intensity across conditions, but rather to the inhibitory effects of cTBS. These findings provide valuable insight into the neural mechanisms underlying the yips and offer a novel foundation for future intervention strategies. REFERENCES: [1] Clarke et al., 2015 Int Rev Sport Exerc Psychol [2] Watanabe et al., 2021 SciRep [3] Huang et al., 2005 Neuron.
Read CV Daiki YamasakiECSS Paris 2023: OP-BM01