ECSS Paris 2023: OP-BM21
INTRODUCTION: Eccentric quasi-isometric (EQI) contractions are gaining attention due to their theorized benefits for muscle endurance, tendon stiffness, and hypertrophy (Oranchuk et al., 2019). However, these claims remain largely speculative. This series of exploratory studies aims to examine the biomechanics, fatigue patterns of EQI contractions, and compare their acute effects with traditional exercise modes METHODS: Three studies examined EQI contractions across different muscle groups and loading conditions. Study 1 investigated EQI knee extensions and flexions in 16 active participants, analysing torque, fatigue, and range of motion (RoM). Study 2 compared plantarflexion EQIs at 75% and 90% of maximal voluntary isometric contraction (MVIC) in 20 participants, assessing contraction time, torque impulse, and fatigue. Study 3 contrasted EQI and isokinetic heavy-slow resistance exercise in 32 participants, evaluating neuromuscular performance, pain, and RoM across multiple time points. RESULTS: Study 1 showed distinct fatigue responses between extensors and flexors, with extensors exhibiting greater peak torque loss (16.6% vs. 13.3%) and shifts in the optimal angle (+7.4%) following EQI contractions. Knee flexors demonstrated higher intra-repetition velocity and more stable RoM across repetitions. Study 2 found no significant effect of EQI on MVIC torque, but EQIs at 75% MVIC resulted in 34% longer contraction duration, 23% greater torque impulse, and 19% increased RoM compared to 90% MVIC. Study 3 demonstrated that EQI induced lower fatigue, pain, and perceived effort than isokinetic heavy-slow resistance exercise while accumulating greater total torque impulse. Additionally, EQI participants experienced a smaller reduction in MVIC force torque post-exercise (η² = 0.16), and pain levels remained significantly lower across all time points (η² = 0.32). CONCLUSION: EQI contractions exhibit distinct biomechanical and fatigue characteristics depending on muscle group and loading conditions. Knee extensors may be more susceptible to EQI-induced fatigue than flexors, and moderate loading (75% MVIC) may optimize torque impulse and RoM in plantarflexion EQIs. Compared to isokinetic heavy-slow resistance exercise, EQI appears to induce less fatigue and post-exercise pain, suggesting potential advantages in rehabilitation settings. However, given the exploratory nature of these studies, further research is required to substantiate these findings and establish practical applications.
Read CV Žiga KozincECSS Paris 2023: OP-BM21
INTRODUCTION: Although crossover fatigue, defined as a decline in maximal voluntary isometric contraction in the non-exercised contralateral homologous muscle, is still debated in the literature, recent studies have shown that eccentric contractions impair contralateral motor performance. However, to date, no study has evaluated the influence of the fatigue level induced in the exercised muscle group on contralateral motor performance fatigue. Therefore, this study aimed to investigate the impact of two exercises involving submaximal unilateral knee extension eccentric contractions, which induce different levels of fatigue, on crossover fatigue. We hypothesized that motor performance-induced fatigue in the exercised muscle group would influence the magnitude of crossover fatigue. METHODS: Fifteen participants, comprising 8 males (aged 22.3 ± 3.6 years) and 7 females (aged 20.1 ± 1.7 years), randomly underwent unilateral submaximal eccentric exercises of the knee extensors performed at 80% of maximal voluntary eccentric contraction (MVEC) until a reduction of 20% (FAT20%) or 40% (FAT40%) in maximal voluntary isometric contraction (MVIC) of the exercised limb (EL) was achieved. Motor performance fatigue (i.e., central and peripheral factors assessed via percutaneous nerve stimulation) were collected before (PRE), immediately after (POST), 2 minutes (POST2), 5 minutes (POST5) and 10 minutes after (POST10) the fatiguing exercises on both the EL and the non-exercised limb (NEL). Perceived motor fatigue and perceived muscle soreness were assessed at PRE, and POST and POST10, respectively. RESULTS: Contralateral motor performance fatigue was evident after both fatiguing exercises (p<0.05). Although the level of fatigue induced in the EL at POST was greater after FAT40% (-44.9 ± 8.9% of MVIC produced at PRE) compared to FAT20% (-24.3 ± 5.9%), this fatigue level did not significantly influence the significant decline in MVIC in the NEL (-8.3 ± 10.2%, vs -8.8 ± 10.5% after FAT20% and FAT40%, respectively). While significantly impaired in the EL (p<0.001), no significant alterations in neuromuscular parameters (i.e., central or peripheral factors) were observed in the NEL. However, a global increase of perceived motor fatigue at POST (p<0.001) and perceived muscle soreness at POST10 in both limbs was observed (p<0.001). Fatigue in the EL was maintained up to 10 minutes in a lower extent after FAT20% compared to FAT40% (PRE-POST2: -17.6% vs -30.9%; PRE-POST5: -15.0% vs -32.7%; PRE-POST10: -15.7% vs -27.2%, respectively). In the NEL, the loss of MVIC at POST10 was no longer significantly different from PRE following FAT20%, whereas it remained significantly altered until POST10 following FAT40%. CONCLUSION: The current study highlights that the level of fatigue in the EL did not influence crossover fatigue in the NEL. Although motor performance fatigue in the EL involved peripheral and central alterations, increased global perceived motor fatigue may likely account for the crossover fatigue in the NEL.
Read CV Serge ColsonECSS Paris 2023: OP-BM21
INTRODUCTION: Exercise-induced fatigue significantly impairs three-point jump shot accuracy by affecting neuromuscular control, including muscle activation patterns and postural balance (1). However, the underlying mechanisms of these impairments remain unclear. Muscle synergies are low-dimensional control modules organized within the central nervous system that coordinate muscle activation to produce efficient movement patterns (2). Synergy analysis offers a valuable approach to understanding how multiple muscles work together to optimize shooting performance (3). This study aimed to compare the muscle synergies of highly trained basketball players during three-point jump shots before and after exercise-induced fatigue to better understand neuromuscular coordination under fatigued conditions. METHODS: Fifteen highly trained male basketball players participated in this study. Fatigue was induced through a high-intensity protocol combining shuttle sprints and vertical jumps to simulate game-related conditions (4). During pre- and post-fatigue testing, participants performed three-point jump shots continuously on force plates until three successful and three unsuccessful attempts were recorded, following a standardized warm-up and immediately after fatigue induction. Surface electromyography (EMG) was recorded from 16 muscles across the trunk, upper, and lower extremities during the shooting task. Muscle synergies were identified using non-negative matrix factorization (NNMF) to compare neuromuscular coordination before and after fatigue (5). RESULTS: We observed five muscle synergies in successful shots before fatigue, which were reduced to four after fatigue. Unsuccessful shots consistently displayed four synergies both pre- and post-fatigue. Fatigue caused a merging of muscle synergies during the preparation phase, shifting from distinct upper and lower limb activation pre-fatigue to continuous co-activation post-fatigue, closely associated with changes in the center of pressure. During the ball elevation phase, the modular organization of muscle synergies remained unaffected with fatigue. However, significant alterations were observed in the motor modules and primitives of synergy 4 (responsible for push-off), particularly in the tibialis anterior (left: d = -1.06; right: d = -1.47) and gastrocnemius lateral (left: d = 1.61; right: d = 1.66) muscles, resulting in distinct muscle activation patterns and temporal shifts. The time-to-peak of synergy 4 vectors occurred significantly earlier before fatigue than after (d = -0.71). CONCLUSION: The changes in the central nervous systems modular control strategies highlight neuromuscular adjustments that are essential for maintaining shooting performance and accuracy under fatigue. Therefore, coaches and athletes should incorporate targeted neuromuscular training programs aimed at optimizing muscle synergy patterns and improving postural control, ensuring athletes can sustain performance even under fatigued conditions.
Read CV Muzhi ZhangECSS Paris 2023: OP-BM21