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The neural drive to the muscle is the primary determinant of the rate of force development (RFD) in the first 50 ms of a rapid contraction. It is still unproven if repetitive rapid contractions specifically impair the net neural drive to the muscles. To isolate the fatiguing effect of contraction rapidity, 17 male adult volunteers performed 100 burst‐like (i.e., brief force pulses) isometric contractions of the knee extensors. The response to electrically‐evoked single and octet femoral nerve stimulation was measured with high‐density surface electromyography (HD‐sEMG) from the vastus lateralis and medialis muscles. Root mean square (RMS) of each channel of HD‐sEMG was normalized to the corresponding M‐wave peak‐to‐peak amplitude, while muscle fiber conduction velocity (MFCV) was normalized to M‐wave conduction velocity to compensate for changes in sarcolemma properties. Voluntary RFD 0–50 ms decreased (d = −0.56, p < 0.001) while time to peak force (d = 0.90, p < 0.001) and time to RFDpeak increased (d = 0.56, p = 0.034). Relative RMS (d = −1.10, p = 0.006) and MFCV (d = −0.53, p = 0.007) also decreased in the first 50 ms of voluntary contractions. Evoked octet RFD 0–50 ms (d = 0.60, p = 0.020), M‐wave amplitude (d = 0.77, p = 0.009) and conduction velocity (d = 1.75, p < 0.001) all increased. Neural efficacy, i.e., voluntary/octet force ratio, largely decreased (d = −1.50, p < 0.001). We isolated the fatiguing impact of contraction rapidity and found that the decrement in RFD, particularly when calculated in the first 50 ms of muscle contraction, can mainly be explained by a decrease in the net neural drive. [ABSTRACT FROM AUTHOR]

Walking and running are based on rapid burst‐like muscle contractions. Burst‐like contractions generate a Gaussian‐shaped force profile, in which neuromuscular determinants have never been assessed. We investigated the neural and contractile determinants of the rate of force development (RFD) in burst‐like isometric knee extensions. Together with maximal voluntary force (MVF), voluntary and electrically evoked (8 stimuli at 300 Hz, octets) forces were measured in the first 50, 100, and 150 ms of burst‐like quadriceps contractions in 24 adults. High‐density surface electromyography (HDsEMG) was adopted to measure the root mean square (RMS) and muscle fiber conduction velocity (MFCV) from the vastus lateralis and medialis. The determinants of voluntary force at 50, 100, and 150 ms were assessed by stepwise multiple regression analysis. Force at 50 ms was explained by RMS (R2 = 0.361); force at 100 ms was explained by octet (R2 = 0.646); force at 150 ms was explained by MVF (R2 = 0.711) and octet (R2 = 0.061). Peak RFD (which occurred at 60 ± 10 ms from contraction onset) was explained by MVF (R2 = 0.518) and by RMS50 (R2 = 0.074). MFCV did not emerge as a determinant of RFD. Muscle excitation was the sole determinant of early RFD (50 ms), while contractile characteristics were more relevant for late RFD (≥100 ms). As peak RFD is mostly determined by MVF, it may not be more informative than MVF itself. Therefore, a time‐locked analysis of RFD provides more insights into the neuromuscular characteristics of explosive contractions. [ABSTRACT FROM AUTHOR]

Women are known to be less fatigable than men in single-joint exercises, but fatigue induced by running has not been well understood. Here we investigated sex differences in central and peripheral fatigue and in rate of force development (RFD) in the knee extensors after a half-marathon run. Ten male and eight female amateur runners (aged 25-50 years) were evaluated before and immediately after a half-marathon race. Knee extensors forces were obtained under voluntary and electrically evoked isometric contractions. Maximal voluntary isometric contraction (MVC) force and peak RFD were recorded. Electrically doublet stimuli were delivered during the MVC and at rest to calculate the level of voluntary activation and the resting doublet twitch. After the race, decreases in MVC force (males: −11%, effect size [ES] 0.52; females: −11% ES 0.33), voluntary activation (males: −6%, ES 0.87; females: −4%, ES 0.72), and resting doublet twitch (males: −6%, ES 0.34; females: −8%, ES 0.30) were found to be similar between males and females. The decrease in peak RFD was found to be similar between males and females (males: −14%, ES 0.43; females: −15%, ES 0.14). Half-marathon run induced both central and peripheral fatigue, without any difference between men and women. The maximal and explosive strength loss was found similar between sexes. Together, these findings do not support the need of sex-specific training interventions to increase the tolerance to neuromuscular fatigue in half-marathoners. [ABSTRACT FROM AUTHOR]

In order to investigate the behaviour of athletes in choosing sports, we analyse data from part of the We-Sport®database, a vertical social network that links athletes through sports. In particular, we explore connections between people sharing common sports and the role of age and gender by applying “network science” approaches and methods. The results show a disassortative tendency of athletes in choosing sports, a negative correlation between age and number of chosen sports and a positive correlation between age of connected athletes. Some interesting patterns of connection between age classes are depicted. In addition, we propose a method to classify sports, based on the analyses of the behaviour of people practising them. Thanks to this brand new classifications, we highlight the links of class of sports and their unexpected features. We emphasise some gender dependency affinity in choosing sport classes. [ABSTRACT FROM PUBLISHER]

ABSTRACT Introduction: We describe the innervation zone (IZ) location in 43 muscles to provide information for appropriate positioning of bipolar electrodes for clinical and research applications. Methods: The IZ was studied in 40 subjects (20 men and 20 women) using multichannel surface electromyography (sEMG). Signal quality was checked visually to identify motor unit action potentials and estimate muscle fiber conduction velocity. Results: Results in 33 muscles were classified as excellent or good, because it was possible to identify an area which is favorable for appropriate positioning of an electrode pair without the need to previously determine the IZ location. Conclusions: Knowledge of IZ location will increase standardization and repeatability of sEMG measures. Muscle Nerve 49:413-421, 2014 [ABSTRACT FROM AUTHOR]

Women are known to be less fatigable than men in single-joint exercises, but fatigue induced by running has not been well understood. Here we investigated sex differences in central and peripheral fatigue and in rate of force development (RFD) in the knee extensors after a half-marathon run. Ten male and eight female amateur runners (aged 25-50 years) were evaluated before and immediately after a half-marathon race. Knee extensors forces were obtained under voluntary and electrically evoked isometric contractions. Maximal voluntary isometric contraction (MVC) force and peak RFD were recorded. Electrically doublet stimuli were delivered during the MVC and at rest to calculate the level of voluntary activation and the resting doublet twitch. After the race, decreases in MVC force (males: −11%, effect size [ES] 0.52; females: −11% ES 0.33), voluntary activation (males: −6%, ES 0.87; females: −4%, ES 0.72), and resting doublet twitch (males: −6%, ES 0.34; females: −8%, ES 0.30) were found to be similar between males and females. The decrease in peak RFD was found to be similar between males and females (males: −14%, ES 0.43; females: −15%, ES 0.14). Half-marathon run induced both central and peripheral fatigue, without any difference between men and women. The maximal and explosive strength loss was found similar between sexes. Together, these findings do not support the need of sex-specific training interventions to increase the tolerance to neuromuscular fatigue in half-marathoners. [ABSTRACT FROM AUTHOR]