Gender differences in muscle blood volume reduction in the tibialis anterior muscle during passive plantarflexion.

Physical flexibility, such as joint range of motion and muscle extension, may influence muscle blood volume. Women have been shown to have a greater degree of flexibility than men. We examined whether there is a gender difference in the relationship between fascicle length and muscle blood volume or oxygenation in untrained men and women. In 16 untrained men and thirteen untrained women, we measured the total-[haemoglobin (Hb) + myoglobin (Mb)] (total-[Hb + Mb]) and relative oxy-[Hb + Mb] after calibrating baseline and arterial occlusion deoxygenation levels with near-infrared spectroscopy. Also, fascicle length was measured with B-mode ultrasonography at the tibialis anterior muscle during passive plantarflexion. Increases in fascicle length from baseline (ankle joint angle 120°, composed from the caput fibulae, the malleolus (pivot), and the distal epiphysis of the fifth metatarsal bone) were greater in women than in men during plantarflexion of 140° and 160° and the maximal angle without pain. However, the decreases in total-[Hb + Mb] and relative oxy-[Hb + Mb] from baseline were not different between women and men at any degree of plantarflexion. Moreover, fascicle length and total-[Hb + Mb]/muscle thickness (men > women) showed a similar relationship, with muscle thickness increasing capillary compression. These findings indicate the possibility of a mechanical function underlying muscle blood volume during muscle stretching, which is greater in women than in men.