ECSS Paris 2023: OP-BM16
INTRODUCTION: Since the rise of powerlifting, consisting of the squat, bench press, and deadlift, calls for biomechanically informed coaching strategies have become increasingly important to maximise performance and enhance technique. Understanding the muscle forces at work can play a key part in this endeavour and musculoskeletal modelling provides a non-invasive and valid means for estimating in-vivo muscle forces [1]. So far, only a small number of musculoskeletal modelling studies focussed on analysing muscle forces during squats in elite athletes [2]. The aim of this study was to investigate the effects of increasing intensity in the squat on muscle forces in elite powerlifters. METHODS: 3D movement data and ground reaction forces were recorded from 29 top-ranked powerlifters (age: 26.1±5.4 years; 1-repetition-maximum: 2.4±0.4 x body mass) performing squats at 70%, 75%, 80%, 85% and 90% of their 1-repetition-maximum. Personalized musculoskeletal models based on the “Catelli”-model [3] were used to estimate muscle forces in OpenSim [1]. Maximum isometric muscle forces of the models were adjusted based on the muscle volumes obtained from magnetic resonance imaging of six athletes [4]. Statistical Parametric Mapping was used to compare muscle forces waveforms throughout the squat across various intensity conditions. RESULTS: While muscle forces increased significantly at higher intensities, the extent of this increase varied between the muscles examined. The gluteus maximus showed the greatest increase in muscle forces (eccentric: +25.1%±8.6; concentric: +24.6%±7.2) and the vasti muscles exhibited the highest absolute muscle forces (eccentric: 13.2±2.4 x body weight; concentric: 12.3±2.5 x body weight) but did not show a significant increase in the deepest position of the squat with increasing intensities. Furthermore, the ratio between the muscle forces of single-joint and multi-joint hip extensors was inversely correlated with the performance level of the athletes. CONCLUSION: According to our results the increase in muscle forces was not uniform between the muscles tested. Consequently, the gluteus maximus could be identified as the muscle increasingly involved at high intensities, while the vasti muscles contributed to the squat with the highest muscle forces. The higher the athletes performance level, the more likely they were to rely on multi-joint hip joint extensors. Athletes should therefore favour a hip dominant squatting style. By tailoring training programmes and fine-tuning squat techniques based on these biomechanical findings, lifters can maximise their performance. 1) Delp et al., IEEE Trans Biomed Eng, 2007 2) Kipp et al., J Strength Cond Res, 2022 3) Catelli et al., Comput Methods Biomech Biomed Engin, 2019 4) Fedorov et al., J Magn Reson Imaging, 2012
Read CV Alexander PürzelECSS Paris 2023: OP-BM16
INTRODUCTION: Recent research has highlighted partial range-of-motion (ROM) exercises as potentially equal or superior to full-ROM training for promoting hypertrophy and strength adaptations [1,2]. However, possible differences in muscle excitation between full and partial ROM—and thus potential mechanisms underlying these adaptations—remain largely unexplored, particularly for upper-body exercises. Therefore, this study investigated the effects of ROM variations during two resistance exercises, bench press (BP) and the prone barbell row (PBR), on muscle excitation. METHODS: Nineteen resistance-trained male participants (24.3±3.1 years) performed 10-repetition-maximum (10RM) sets of the BP and PBR in three ROM conditions: full ROM, upper-half ROM, and lower-half ROM. Surface electromyography (sEMG) was recorded from primary muscles (BP: pectoralis major [clavicular, sternocostal], triceps brachii [long, lateral], anterior deltoid; PBR: latissimus dorsi, trapezius transversus, rear deltoid, biceps brachii). BP repetitions were standardized by controlling movement velocity (2s up, 2s down for full ROM; 1s up, 1s down for partial ROMs), whereas the row was standardized by matching total time under tension (2s up, 2s down) across all ROMs. Mean and peak sEMG amplitudes were analyzed across repetitions. A repeated measures ANOVA (one factor, levels: full ROM, upper-half ROM, lower-half ROM) assessed possible differences in performance and muscle activity. Bonferroni post-hoc tests followed significant main effects. The alpha level was set to p≤0.05. RESULTS: In the BP, significant differences (p<0.01) in mean sEMG were found across all tested muscles for the three ROM conditions. The upper-half ROM showed the highest mean excitation in the triceps, while both partial-ROM conditions showed greater mean excitation in the pectoralis major and anterior deltoid compared to the full ROM. For the PBR exercise, the latissimus dorsi exhibited significantly greater mean excitation during the upper-half ROM compared to lower-half and full ROM (p<0.01), whereas the trapezius transversus showed lower peak excitation in the upper-half ROM (p<0.05). CONCLUSION: In summary, these findings highlight that partial-ROM strategies can alter muscle excitation in both pushing and pulling exercises. Moreover, the method of standardization (i.e., movement velocity versus total time under tension) may influence the observed activation patterns. However, these results are based on the acute relationship between muscle excitation and ROM and do not provide direct insights into long-term adaptations [3,4]. Future research should investigate how these excitation patterns translate to changes in muscle hypertrophy and strength over time. 1. Pedrosa et al. 2022. European Journal of Sport Science.22(8), Article 8. 2. Kassiano et al. 2022. International Journal of Sports Medicine. 43(03), Article 03. 3. Vigotsky et al. 2018. Frontiers in Physiology. 14, 1279170. 4. Plotkin et al. 2023. Frontiers in Physiology. 8, 985.
Read CV Josef FischerECSS Paris 2023: OP-BM16
INTRODUCTION: The nervous system controls the activation of hip muscles according to the magnitude and direction of the muscle forces required during various movements (1). The mechanical action of each muscle is traditionally estimated as the projected moment arm vector (2). However, it remains unclear whether neuromuscular activation is appropriately regulated according to its mechanical action. To investigate this, we developed a novel method to quantify the direction in which a muscle exhibits the highest level of neuromuscular activation among multiple external force directions (the optimal activation angle). This study aimed to determine the optimal activation angles of hip muscles and evaluate their deviations from the projected moment arm vector in the transverse plane. METHODS: Eight male participants performed maximum voluntary isometric contractions (MVICs) for 3 s in eight directions (hip adduction, flexion, abduction, extension, and in between them [every 45°]) at the hip flexed by 0° and the knee flexed by 90°. Surface electromyograms (EMG) were recorded from the major 14 hip muscles. A root mean square (RMS) of EMG during MVICs (1 s) and corresponding direction of exeternal force were plotted in a polar coordinate system, with the RMS as the radius and direction of exeternal force as the angle from the polar axis. For each muscle, the centroid of the eight MVICs was calculated in the polar coordinates. The optimal activation angle for each muscle was defined as the angle of the line connecting the centroid and the pole from the polar axis. The projected moment arm vector was calculated using the musculoskeletal simulation model (OpenSim) for each muscle. The Wilcoxon signed-rank test was used to compare the optimal activation angle with the projected moment arm vector. RESULTS: The optimal activation angles deviated from the projected moment arm vector in the sartorius, adductor longus and magnus, gracilis, biceps femoris long head, upper and lower parts of gluteus maximus, and anterior part of gluteus medius (12.0-63.5° [all p < 0.05]). However, the optimal activation angles of the other six muscles did not deviate from the projected moment arm vector. CONCLUSION: Our findings showed that the optimal activation angles of several hip muscles deviated from their projected moment arm vector, with the lower part of gluteus maximus exhibiting deviations over 60°. These results suggest that certain hip muscles prioritize other functions (e.g., joint stabilization) rather than their mechanical actions. Training exercises that considering the optimal activation angle of the target muscles may be more effective than traditional exercises based on their mechanical actions. REFERENCES 1) d’ Avella et al. Nat Neurosci (2003) 2) Horsman et al. Clin Biomech (2007)
Read CV Hironoshin TozawaECSS Paris 2023: OP-BM16