Intensity-dependent effect of ageing on fatigue during intermittent contractions of the human calf muscle in males and females

Ageing reduces fatigue during submaximal intermittent contractions, but the influence of intensity on this ageing effect in males and females is not clear. Younger males (n = 8; 23 ± 2 years), younger females (n = 8; 22 ± 1 years), older males (n = 8; 67 ± 5 years) and older females (n = 10; 64 ± 7 years) completed intermittent calf contractions at four submaximal intensities (30–70 %MVC) for up to 20 min. MVC was assessed during exercise at 30–60 s intervals and its linear rate of decline represented fatigue. Individual relationships between intensity and fatigue (%MVC min⁻¹) were fitted to a biphasic function consisting of a linear and nonlinear component. There was no age × sex × intensity interaction for fatigue (3-way ANOVA, P = 0.46). However, there were significant interactive effects of age and sex on endurance at 70 %MVC, fatigue at 70 %MVC and the linear component of the intensity–fatigue relationship. Endurance was lower and fatigue and its linear component were greater (P < 0.05) in younger males compared with other groups, but not different between younger and older females. This suggests that there is an intensity-dependent effect of human ageing on fatigue during submaximal exercise that is specific to males.