Gender Differences In Muscle Strength , Blood Flow And Oxygen Consumption Recovery From Intermittent Handgrip Exercise

Abstract

Several studies have suggested that women may have greater resistance to skeletal muscle fatigue than men. Blood flow and oxygen consumption in working muscles are critical factors for muscle performance, fatigue-resistance, and muscle strength recovery from exercise. However, the mechanisms causing gender differences in muscle strength recovery from exercise are unclear. PURPOSE To investigate a mechanism causing gender differences in skeletal muscle fatigability, we examined whether there is a difference in muscle blood flow and oxygen consumption after intermittent handgrip exercise between men and women using near-infrared spectroscopy (NIRS) and high resolution ultrasound system. METHODS Healthy young (24.6±2.8 years) men (n =5) and women (n =5) laid supine and repeated static contractions of handgrip muscles at 100% maximal voluntary contraction (MVC) for 5 seconds followed by 5 seconds rest for 4 minutes. The MVC force was measured before, each minute during, and 2, 5, and 10 minute after the end of the exercise. We measured total-and deoxy-hemoglobin/myoglobin level by venous occlusion NIRS method, and calculated O2 supply index (OSI) and O2 consumption index (OCI), as follows OSI=[d(total Hb/Mb)/dt]·SaO2±100−1(OD/ min), OCI=[d(deoxy Hb/Mb)/dt]-[d(total Hb/Mb)/dt]·(1-SaO 2)·100−1(OD/min). The % MVC, %OSI, and %OCI were calculated as relative changes to the pre-exercise values. Simultaneously, forearm blood flow (FBF) was measured by a high resolution ultrasound system. RESULTS No gender difference was found in MVC force decline during the exercise. However, the force recovery was significantly faster in women than in men at minutes 5 (80.8±6.1 vs. 66.3±12.7 %MVC, p < 0.05) and 10 (86.0±5.8 vs. 71.8±11.7 %MVC, p < 0.05) of recovery. The %OSI was significantly lower in women than in men at minutes 5 (128.0±28.7 vs. 177.8±23.5 %OSI, p < 0.05) and 10 (111.2±8.3 vs. 156.1±39.7 %OSI, p < 0.05) of recovery, but no significant effects of gender were detected in %OCI. Although absolute FBF was less in women than in men before and after the exercise, %FBF was not different between groups. Furthermore, %MVC of recovery tended to correlate with %OCI of recovery in women (r=0.548, p=0.077), but not in men. CONCLUSION These findings suggest that women recovered their strength faster after intermittent handgrip exercise compared with men, and the observed differences that women more effectively consumed oxygen supplied to the working muscles may be linked with the underlying mechanisms causing gender differences in skeletal muscle fatigability.