Forearm Blood Flow is Similar Between Females and Males During Dynamic Submaximal Handgrip Exercise

Abstract

Muscle blood flow has been discussed as a possible factor contributing to observed sex differences in exercise tolerance. PURPOSE: To determine if forearm blood flow (FBF) is related to sex differences in exercise tolerance during dynamic forearm muscle contractions performed during a similar absolute task. METHODS: Fifteen females [24.3 ± 4.0 (SD) yr] and 16 males (24.9 ± 4.5 yr) of similar age performed intermittent handgrip exercise in a ramp function (0.5 kg-min-1) while supine with forearm at heart level. Task failure was denned as the inability to maintain contraction frequency (30 cpm) or duty cycle (0.2 s: 1.8 s). Motor unit recruitment and FBF were measured continuously during the exercise test using surface electromyography and Doppler ultrasound, respectively. RESULTS: Forearm volume was smaller (P<0.05) in females (836.9 ± 185.7 ml) than males (1291.9 ± 282.6 ml) along with isometric maximal voluntary contraction (MVC) force (F: 290.7 ± 44.4 N, M: 509.6 ± 97.8 N, P<0.05). Muscle strength was linearly related to forearm volume (pooled data, r2 = 0.79, P<0.01). Time to task failure was less for females than males (F: 450 ± 113 s, M: 831 ± 273 s, P<0.05) thus the workload achieved at task failure was greater (P<0.05) in males (M: 7.4 ±1.9 kg) than females (F: 4.2 ± 0.8 kg). However, exercise intensity achieved at task failure as a percent of their initial isometric MVC was similar between sexes (F: 14.3 ± 2.5% MVC, M: 14.2 ± 2.1 % MVC). No sex difference was found in FBF throughout forearm exercise or at task failure (F: 13.6 ± 5.3 ml-mm-1-lOOml-1, M: 14.5 ± 4.9 ml-min-l-100ml-l). In addition, the percent increase in motor unit recruitment from unloaded contractions to task failure was similar between females (425.6 ± 149.1%) and males (528.9 ± 302.9%). CONCLUSION: These findings suggest that FBF is not a contributing factor to sex differences in exercise tolerance during dynamic submaximal handgrip exercise.