ECSS Paris 2023: OP-BM26
INTRODUCTION: Eccentric muscle actions, which generate high force at relatively low metabolic cost, often induce muscle damage and prolonged neuromuscular fatigability. The results of these mechanisms are evident in ecological situations, such as mountain trail running and other eccentric-intensive tasks. Such eccentric-induced deficits have important functional consequences: for instance, the ability to quickly manage terrain roughness to avoid potential accidents/injuries or the balance recovery after a sudden slip must occur within ≈100 ms. Thus, the ability to develop force rapidly, quantified as the rate of force development (RFD), is often more critical than maximal strength alone. Moreover, many real-world gestures involve submaximal forces. To address this, the RFD scaling factor (RFD-SF) has been proposed as a novel metric to assess rapid force capacity across submaximal intensities. We aimed to analyze the impact of a fatiguing incremental eccentric cycling task on muscle voluntary force (MVF), RFD (peak and time-locked window), and RFD-SF. METHODS: A within-subject, repeated-measures design was used to quantify the acute effects on knee extensor neuromuscular function. 38 healthy participants (31 men, 7 women; 23 ± 1 years) completed two sessions 10–15 days apart. Visit 1 served as a familiarization and Visit 2 as a neuromuscular assessment before and immediately after the incremental eccentric cycling task, until voluntary exhaustion (from 100W for males and 50W for females + 25W·min⁻¹). The primary dependent variables were MVF, RFDpeak, time-locked RFD50, 100, 150, and RFD-SF, derived from ≥ 48 ballistic isometric knee-extension contractions performed across 20, 40, 60, and 80% MVF targets in blocks randomized across participants and matched PRE–POST within participants. RESULTS: Linear mixed models indicated that, even after a prior identical eccentric exposure (to account for the repeated-bout effect), MVF decreased by ≈16% (p < 0.001; d = −3.34), RFD declined across all windows (RFD50: −9.3%, p < 0.05, d = −0.53; RFD100: −7.5%, p < 0.001, d = −1.00; RFD150: −8.4%, p < 0.001, d = −1.49) and RFDpeak decreased by −9.1% (p < 0.01; d = −0.84); additionally, the RFD-SF slope decreased by ≈5% (p < 0.01; d = −0.68), indicating reduced rapid force capacity across submaximal targets. CONCLUSION: An incremental eccentric cycling task induced marked reductions in MVF and in the ability to generate force rapidly, even after a prior eccentric exposure, highlighting RFD and RFD-SF as sensitive markers of acute fatigability. Because many athletic tasks have a large eccentric component, these impairments may compromise rapid reactive actions on technical terrain or during repeated decelerations. From a practical perspective, coaches should therefore monitor and periodize eccentric load, avoiding exhaustive bouts before power/agility-demanding sessions; conversely, eccentric pre-conditioning may be used strategically to elicit adaptation while attenuating damage on subsequent exposures.
Read CV Samuel DEmanueleECSS Paris 2023: OP-BM26
INTRODUCTION: Individuals with Amyotrophic Lateral Sclerosis (ALS) experience progressive degeneration and eventually death of their motor neurons, leading to muscle atrophy and weakness [1]. As the disease advances, surviving motor neurons partially compensate for this loss through collateral sprouting, resulting in the formation of enlarged motor units (MUs) [2]. These structural adaptations alter the shape and discharge patterns of motor unit action potentials (MUAPs) [3]. This study aims to investigate differences in MU characteristics during voluntary contractions at three force intensities between individuals with ALS and sedentary healthy controls using a novel, non-invasive technique called high-density surface electromyography (HDsEMG). METHODS: Participants (ALS: n=9, females=11%, age=60±13 years; healthy: n=9, females=56%, age=60±14 years) performed maximal (MVC) and submaximal isometric voluntary contractions (35%, 50%, and 70% of MVC) of the ankle dorsiflexors on an isokinetic dynamometer. HDsEMG recordings were obtained from the tibialis anterior using a 64-electrode grid. MUs were identified using a convolutive blind source separation method. MUAP peak-to-peak values, area, and MU spatial and discharge characteristics were assessed and compared between the two populations. RESULTS: There was no significant difference in the MVC between groups (ALS: 21.9±13.2 Nm, healthy: 23.7±8.5 Nm; p=0.747). On average, 9 MUs were identified in participants with ALS, compared to 10 in healthy controls across all force levels. There was no significant difference between groups for MU activity within the electrode grid (ALS: 454±89 mm2, healthy: 486±168 mm2; p=0.911). MU characteristics were significantly altered in participants with ALS compared to healthy controls including larger MUAP peak-to-peak amplitudes (391±143 µV vs. 277±202 µV; p=0.027), greater MUAP areas (2689±1111 µV·ms vs. 1843±12587 µV·ms; p=0.007) and higher MU discharge rates (17±5 pps vs. 13±3 pps; p<0.001). The MU recruitment thresholds were increased in ALS (58±21 %MVC vs. 48±13 %MVC; p=0.048) while the de-recruitment thresholds did not differ between groups. CONCLUSION: The increased MUAP peak-to-peak amplitude, MUAP area, discharge rate, and higher recruitment threshold in the participants with ALS indicate MU remodelling, where collateral sprouting leads to enlarged MUs and require a greater synaptic input. These findings suggest that HDsEMG could serve as a powerful tool for future studies, allowing more detailed identification of MU changes and a deeper understanding of ALS progression and the effects of interventions. [1] Gordon, P.H. (2013), Aging and disease. [2] Nijssen, J. et al (2017), Acta Neuropathologica. [3] Krarup, C. et al (2011), Clinical Neurophysiology.
Read CV Patricia BayerECSS Paris 2023: OP-BM26
INTRODUCTION: When applied to a muscle, local vibration (LV) can decrease its maximum force output. Previous studies indicate that the magnitude of force reduction increases with longer durations of vibration exposure. Beyond force modulation, LV has also been shown to increase range of motion (ROM) and decrease passive torque. Whether LV modulates maximal force production and ROM when applied to the tendons remains unclear due to inconsistent LV parameters and its frequent application following exercise sessions or in combination with stretching interventions. To the best of our knowledge, no study has investigated the acute effects of prolonged LV applied to the hamstring tendons during rest. Therefore, the objective of this study was to investigate the effects of a 30-min tendon LV on maximal voluntary isometric contraction, ROM, and passive torque at rest. METHODS: 17 recreationally active adults participated in a randomized cross-over study. Each participant completed two experimental sessions separated by at least 48 hours, one with local vibration (LV), and one control condition (CC). LV (100 Hz, 2-3 mm) was applied for 30 minutes to the distal tendons of the biceps femoris and semitendinosus while participants remained in a passive seated position. Surface electromyographic (sEMG) activity was recorded to verify muscle relaxation during both conditions. Maximal voluntary isometric contraction (MVIC), ROM, and passive torque during a passive knee extension test were assessed 1 min before and immediately after each condition. A repeated-measures ANOVA was used to examine the effects of Time and Condition. RESULTS: The ANOVA revealed a significant main effect of Time for ROM (p = 0.045), indicating an increase from pre- to post-measurement independently of the condition. No significant main effect of Condition (p = 0.227) nor Time × Condition interaction (p = 0.995) was observed. Passive torque showed no significant effects of Time (p = 0.536), Condition (p = 0.803), nor interaction (p = 0.646). For MVIC, a significant main effect of Time was detected (p = 0.001), reflecting a decrease in maximal voluntary strength from pre- to post-measurement independently of the experimental condition. No significant main effect of Condition (p = 0.548) nor Time × Condition interaction (p = 0.815) was found. CONCLUSION: The results suggest that prolonged tendon-targeted LV alone does not induce acute changes in hamstring flexibility or passive mechanical properties compared to the control condition, whereas strength performance declines over time regardless of intervention. Further research should examine whether LV applied to tendons or muscles yields similar neuromuscular adaptations under different vibration frequencies and application parameters.
Read CV CHRISTOS PAIZISECSS Paris 2023: OP-BM26