Collins JD, et al. - In a cohort of young and older working age males and females, researchers investigate age and sex-related differences in manifestations of shoulder muscle fatigue in a single experiment design allowing for direct comparison of the fatigue effects between the target groups. Trapezius muscle fibre Conduction Velocity (CV) was reported as an indicative measure of muscle fatigability, and isometric endurance time, at three levels of shoulder abduction lifting force set relative to participants’ maximal strength. As per findings, muscle fatigue resistance improved in correlation to age, and females showed increased resistance over males, contrary to injury prevalence trends. Muscle fibre type composition seems to underlie the muscle fatigue effects. Relative to the participants’ strength, experimental fatigue treatments of the upper trapezius were tested at exposures. At a young age, absolute strength is higher and it is higher for males generally. The differences in the injury trends seemed to be primarily due to age and sex-related differences in strength rather than in muscle fatigue resistance.