Abstract
Previous investigations have demonstrated that time to exhaustion (TTE) is shorter in males compared to females during sustained submaximal isometric contractions. This discrepancy has been attributed to males generating a greater absolute force at the same relative intensity causing occlusion of the vessel supplying blood to the working muscle. PURPOSE: To determine if differences in muscle blood flow (MBF) between sexes is associated with a reduced TTE in males compared to females during isometric handgrip exercise. METHODS: Eighteen subjects (9 male and 9 female, 24 ± 1 yrs (± SE)) performed isometric handgrip exercise at a target force requiring 20%, 50%, or 80% maximal voluntary contraction (MVC) on 3 separate occasions. TTE was determined when the subject could no longer maintain force within 5% of the target value. Forearm flexor muscle activity was measured using surface electromyography (EMG) and analyzed in the time domain (integrated EMG). Brachial artery blood velocity was measured continuously during exercise using Doppler ultrasonography and corrected to MBF by obtaining brachial artery diameter at rest. Forearm volume was determined by water displacement and MBF was expressed both in absolute and relative values. To analyze MBF responses between subjects, TTE was normalized to 100% and compared at 10% intervals. RESULTS: Males (401 ± 62 N) generated greater absolute force compared to females (215 ± 45 N). Although TTE decreased (p<0.05) with an increase in contraction intensity, there was no significant difference in TTE between sexes. At 20% MVC, absolute MBF increased (p<0.05) from rest to TTE in both males (80.3 ± 42.6 ml/min) and females (50.3 ± 22.3 ml/min). At TTE >60% absolute MBF was higher (p<0.05) in males compared to females. There was no difference in absolute MBF between sexes at 50% MVC. However, absolute MBF was reduced in males only during 50% MVC compared to 20% MVC. Expressed relative to forearm volume, MBF was similar between sexes at 20% and 50% MVC. MBF could not be measured at 80% MVC for either sex. EMG increased (p<0.05) with contraction intensity, and time, but no difference between the sexes was observed. CONCLUSIONS: Despite females generating less absolute force, the similar TTE between sexes and the lower absolute MBF in females then males at 20% MVC suggests that factors other then MBF and/or vascular occlusion explain the longer exercise times for females observed in other studies. When MBF was adjusted for forearm volume, differences in MBF between the sexes were eliminated suggesting that MBF was appropriate for the exercising muscle mass, independent of sex. Supported by deArce Memorial Endowment Fund, The University of Toledo
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call