A sex-specific relationship between capillary density and anaerobic threshold

Although both capillary density and peak oxygen consumption (V̇O ₂) improve with exercise training, it is difficult to find a relationship between these two measures. It has been suggested that peak V̇O₂ may be more related to central hemodynamics than to the oxidative potential of skeletal muscle, which may account for this observation. We hypothesized that change in a measure of submaximal performance, anaerobic threshold, might be related to change in skeletal muscle capillary density, a marker of oxidative potential in muscle, with training. Due to baseline differences among these variables, we also hypothesized that relationships might be sex specific. A group of 21 subjects completed an inactive control period, whereas 28 subjects (17 men and 11 women) participated in a 6-mo high-intensity exercise program. All subjects were sedentary, overweight, and dyslipidemic. Potential relationships were assessed between change in capillary density with both change in V̇O₂ at peak and at anaerobic threshold with exercise training. All variables and relationships were assessed for sex-specific effects. Change in peak V̇O₂ was not related to change in capillary density after exercise training in either sex. Men had a positive correlation between change in V̇O₂ at anaerobic threshold and change in capillary density with exercise training (r = 0.635; P < 0.01), whereas women had an inverse relationship (r = -0.636; P < 0.05) between the change in these variables. These findings suggest that, although enhanced capillary density is associated with training-induced improvements in submaximal performance in men, this relationship is different in women.