ECSS Paris 2023: OP-AP41
INTRODUCTION: Neuromuscular fatigue may be defined as an exercise-induced reduction in the force-generating capacity of muscle (1). It is a complex phenomenon involving a range of neural and muscular mechanisms. Previous research has suggested that there is a difference in the functional organization of the neuromuscular system between strength-trained (ST) and endurance-trained (ET) males (2), which may lead to different neuromuscular responses to fatigue. Research into the effects of fatigue in differentially trained individuals has mainly focused on dynamic exercise, whereas studies on sustained isometric fatiguing tasks remain limited. These can provide a paradigm in which the contribution of individual mechanisms may be more easily observed. The aim of this study was to assess the neuromuscular fatigue in recreationally ST males and ET runners during a sustained submaximal isometric knee extensor contraction. METHODS: Eleven ST (21.5 ± 2.9yr) and 11 ET (19.8 ± 2.4yr) males volunteered for the study. Participants performed maximal voluntary isometric contractions (MVICs) of the knee extensors before and immediately after submaximal isometric knee extension at 30% MVIC until task-failure. High-density surface EMG was simultaneously recorded from the vastus lateralis muscle. EMG root mean square (RMS), median frequency (MDF) and muscle fibre conduction velocity (MFCV) were estimated. RMS and MDF post-fatigue were normalized with respect to their pre-fatigue MVIC values. RMS%, MDF% and MFCV were examined at intervals corresponding to 10% of the contraction time. RESULTS: ST were 43% stronger (p<0.01) than ET with a higher BMI (24.7 vs 21.1kg/m2; p<0.001). No differences were observed in post-fatigue MVIC (20.6 vs 22.5%) or time-to-failure between groups. However, MDF% decreased by 8.7% in ST, while it remained unchanged in ET (p<0.05) in post-fatigue MVIC. During the fatiguing task, MFCV was lower in ET compared to ST (4.4 vs 4.7 m/s, p<0.05). Moreover, the linear mixed model revealed a decrease in MFCV (p<0.05) and MDF% (p<0.001) in ST, whereas they were unchanged in ET throughout the contraction. The increase in RMS% was similar between the two groups (p<0.001). CONCLUSION: In this study, both groups exhibited similar time-to-failure or reductions in MVIC%. However, ST showed a decrease in MDF% and MFCV during the fatiguing task, whereas ET remained unchanged. Additionally, MFCV was higher in ST compared to ET, suggesting that the muscle fibres with a larger cross-sectional area were recruited in ST. These findings indicate that while submaximal isometric fatiguing task induced comparable fatigue in both groups, the underlying neuromuscular fatigue mechanisms differ, likely due to a greater percentage of type II fibres and/or a greater relative area of type II fibres in ST. REFERENCE: 1) Blgland-Ritchie & Woods, Muscle & Nerve 1984 2) Pääsuke, M. et al., Acta Physiol Scand 1999
Read CV Rui WuECSS Paris 2023: OP-AP41
INTRODUCTION: Sex differences in performance fatigability of limb muscles are specific to the task demands, and can vary according to the contraction type, speed and intensity or the involved muscle groups (1). In this line, research has consistently shown that women experience less fatigue than men during and in response to isometric and slow, dynamic-contraction tasks (performed at the same relative intensities) (2); however, less is clear about fast-dynamic contractions. In addition, monitoring velocity loss (VL) throughout a set provides accurate information about the level of effort generated during the training session (3). This study aimed to compare the acute and short-term mechanical and metabolic responses in women and men with similar levels of strength performance (4) after a resistance training (RT) session in bench press (BP) exercise. METHODS: Thirty-one participants (16 women and 15 men) performed a single RT bout in BP exercise: (load: 70% of one-repetition maximum (1RM), sets: 3, velocity loss VL: 50%, rest: 3 min). Before the performing protocol a previous session was carried out to obtain the 1RM and individualized load-velocity relationship. Measurement session involved recordings at different time points: pre-exercise (Pre), post-exercise (Post), 10-minute post (Post-10), and 24-hour post (Post-24), of different variables: mean propulsive velocity (MPV) of the load of 60% 1RM in the BP (Load-60) and lactate. In addition, the number of repetitions in each set and the total number of repetitions were registered and analyzed. RESULTS: No significant “Sex × time” interaction was found for any variable. However, the lactate displayed a tendency toward a significant “Sex × time” interaction (p=0.07), with higher increments for men compared to women. A significant “Time effect” (p<0.001) was obtained for MPV Load-60, with a similar response in women and men in Post and Post-10 with respect to Pre (p<0.001), and both sexes were recovered at Post-24. A significant “Sex effect” was reported for total repetitions (p= 0.019), women completed significantly more repetitions in set 2 (8.3 ± 2.0 vs. 6.9 vs. 1.3; p= 0.03), set 3 (7.6 ± 1.9 vs. 6.1 ± 1.0: p= 0.01), and during all session (24.8 ± 5.1 vs. 21.1 ± 2.7; p= 0.019). CONCLUSION: Our results provide evidence about sex-differences in the acute and short-term fatigability after a BP training session when equalizing the strength performance level, the intensity, and volume through VL. Although no significant differences between sexes were found in the mechanical response at different time points, higher metabolic responses were observed for men compared to women, despite the higher number of repetitions performed by women. REFERENCES 1) Hunter., Cold Spring Harb Perspect Med, 2018 2) Ansdell et al., J Physiol, 2019 3) Sánchez-Medina et al., 2011 4) Santos Junior et al., Strength and Cond J, 2021
Read CV Beatriz Bachero MenaECSS Paris 2023: OP-AP41
INTRODUCTION: This study compared the effects of mental fatigue and locomotor muscle fatigue on endurance performance, perception of effort and physiological responses in a group of well-trained and elite cyclists. METHODS: Seven performance level 4 and three level 5 (21.8 ± 2.7 yrs, 8 Male 68.4 ± 2.5 VO2Max and 438.8 ± 50.1 PPO, 2 Female 58.7 ± 5.4 VO2Max and 335.0 ± 14.1 PPO) have been recruited for this study. During the first visit to the laboratory, all participants performed an incremental ramp test on a cycle ergometer to determine the respiratory compensation point (RCP), VO2Max and Peak Power Output (PPO). In the subsequent three visits, participants performed TTE at the power corresponding to 95% RCP under three different conditions: 1) Mental fatigue (MF) induced by a 1-hour psychomotor vigilance task (PVT); 2) Locomotor muscle fatigue (LMF) induced by a 100-drop jumps protocol; 3) Watching documentaries was used as a control condition. The order of the three visits was randomly assigned. Physiological and psychological responses measured during the TTE test included heart rate (HR), VO2, ventilation, blood lactate concentration (La) and rating of perceived exertion (RPE). Manipulation checks included maximal voluntary contraction (MVC) of the knee extensors, PVT performance and perceived physical and mental fatigability scales. One-way (condition) or two-way (condition x time) repeated measure ANOVAs were used to analyse the data. Significance was set at p<0.05. The individual isotime method 1 was used to analyse the responses to the TTE test. RESULTS: Manipulation checks revealed mixed results, with only PVT performance influenced by MF (p<0.001) and only perceived physical fatiguability affected by LMF (p<0.001). No significant differences in TTE were found between conditions (Control 989±122s, MF 1019±137s, LMF 973±145s, p=0.876). The RPE and HR at individual isotime in the LMF condition tended to be higher compared to the control condition but these effects were not significant (p=0.081 and p=0.090). No significant effects were found for the other physiological responses. CONCLUSION: The results of this study confirm previous investigations 2 suggesting that well-trained and elite cyclists are resistant to the negative effects of MF. The current study also suggests that well-trained and elite cyclists may also be resistant to the negative effects of LMF experimentally induced in the laboratory. Larger studies are required to confirm these findings and to investigate the “dose” of MF and LMF that may eventually reduce the performance of high-level cyclists. References 1. Nicolò, A. et al. A comparison of different methods to analyse data collected during time-to-exhaustion tests. Sport Sci. Health 15, 667–679 (2019). 2. Martin, K. et al. Superior Inhibitory Control and Resistance to Mental Fatigue in Professional Road Cyclists. PLoS One 11, e0159907 (2016).
Read CV Tullio SenatoreECSS Paris 2023: OP-AP41