Sex differences in neuromuscular fatigability in response to load carriage in the field in British Army recruits

Abstract

Objectives: Women are resistant to neuromuscular fatigue compared to men in response to a range of exercise tasks. The sex differences in the neuromuscular responses to load carriage have yet to be investigated.

Design: Prospective cohort study.

Methods: Twenty-three male and 19 female British Army recruits completed a 9.7km loaded march within 90min, with the weight carried dependent on military trade (16±2kg for men and 15±1kg for women). Isometric maximal voluntary contraction (MVC) force of the knee extensors and vertical jump (VJ) height were examined pre- and post-loaded march to examine neuromuscular fatigue. Heart rate (HR) was recorded throughout and ratings of perceived exertion (RPE) was recorded following the march.

Results: HR was higher for women (173±9bmin^-1, 83±6% heart rate reserve) than men (158±8bmin^-1, 72±6% heart rate reserve) (p≤0.001). RPE following the march was also higher for women than men (6±2 vs 4±2, respectively, p<0.001). The loss in MVC force was greater for men than women (-12±9% vs -9±13%, respectively, p=0.031), however VJ height was impaired to a similar extent (-5±11% vs -5±6%, respectively, p=0.582).

Conclusions: The greater physiological stress during load carriage for women compared to men did not translate to a greater severity of knee extensor muscle fatigue, with women demonstrating fatigue resistance.

Keywords: Exercise physiology; Load carriage; Military personnel; Muscle fatigue; Muscle strength.