Identifying sex differences in neuromuscular fatigue: the challenge of normalizing exercise intensity and interpreting the results between populations

Time Course of Performance Fatigability during Exercise below, at, and above the Critical Intensity in Females and Males

“…In addition, it has been suggested that females have diminished amplitude in the decline of VA compared with males, probably because of lower intramuscular metabolic disturbance and thus less muscle-specific afferent feedback (14,49). However, our data and other findings (7,8) do not support this view when exercise intensity is normalized to relative metabolic stress (i.e., MLSS in our study), which is of utmost relevance to compare physiological responses between sexes (12,24). As a result of the normalization of exercise intensity between females and males (i.e., exercise intensities around each participant’s MLSS), there might have been similar relative afferent feedback to the central nervous system from the active and auxiliary musculature, as well as corollary discharge rate during the exercise (2,3), ultimately leading to the same decline in VA between sexes.…”

“…For example, the rate of decline in contractile function has been shown to be either similar (19)(20)(21) or greater (7,22,23) in males compared with females. This uncertainty may be related factors such as i) the absence of performance fatigability assessments (20); ii) distinct task characteristics, such as amount of muscle mass involved and/or contraction type (7,19,22,23); and iii) lack of precise exercise intensity normalization according to each individual's metabolic responses, which, as recently highlighted elsewhere (24), leads to poor quantification of the metabolic stress (12,(25)(26)(27).…”