Gender differences in muscle force and oxygenation recovery from intermittent handgrip exercise

To investigate a relationship between gender differences in recovery from skeletal muscle fatigue and muscle oxygenation, we examined whether there is a difference in oxygen supply and consumption of the working muscles after intermittent handgrip exercise between young males and females using near-infrared spectroscopy (NIRS). Healthy young subjects (25.8 +/- 3.9 years; males, n=10; females, n=10) repeated static maximal voluntary contractions (MVC) with a handgrip for 5 seconds followed by 5 seconds rest for a period of 4 minutes in Study 1. The MVC force was measured before, each minute during the handgrip exercise, and 2, 5, and 10 minutes following the exercise. In Study 2, the selected 10 subjects (males, n=5; females, n=5) performed the same exercise and their total- and deoxy- hemoglobin/myoglobin level was measured using the venous occlusion NIRS method; and O-2 supply index (OSI) and O-2 consumption index (OCI) calculated before and after the exercise. In Study 1, females exhibited higher %MVC force at the end of the exercise and during the recovery period than males (p < 0.05). In Study 2, the %OSI was significantly lower in females than in males at 5 and 10 minutes in the recovery period (p < 0.05), but no significant differences were detected in %OCI. Furthermore, %MVC of the recovery period correlated with %OCI of the recovery period in females (r=0.724, p=0.015), but not in males. These findings suggest that female working muscles can convert consumed oxygen more effectively after an intermittent handgrip exercise, and therefore, be able to recover muscle force faster.