(1) SEX-DEPENDENT DEVELOPMENT OF PERIPHERAL FATIGUE WITH AND WITHOUT BLOOD FLOW RESTRICTION

Abstract Details: PURPOSE. This study examined the sex-related differences in peripheral fatigue resulting from exhaustive, intermittent isometric forearm flexion exercise performed with and without blood flow restriction (BFR). METHODS. Eight men and eight women (24±6yrs) completed isometric trapezoidal muscle actions to failure at 50% maximal voluntary contraction (MVC) under control conditions (CON) and with BFR, on two separate days. The trapezoidal muscle action increased 10%MVC·s-1 to 50% MVC which was maintained for 12 s, followed by a 10% MVC·s-1 decline to baseline. For the BFR day, a cuff was inflated to 60% of the pressure required for full brachial artery occlusion at rest. The participants received peripheral nerve stimulation at the musculocutaneous nerve before and immediately after exercise to assess peripheral fatigue (peak-to-peak twitch force [twitch force-PP]). A 2 (condition: CON, BFR) x 2 (sex: men, women) ANOVA was used to examine repetitions completed. Separate 2 (condition: CON, BFR) x 2 (pre-, post-exercise) x 2 (sex: men, women) ANOVAs were used to examine change in MVC and twitch force-PP. RESULTS. There was a main effect of condition (p=0.036; =0.277) on repetitions completed that indicated more repetitions were completed during CON (14±8 reps) compared to BFR (10±10 reps). There was a main effect on condition (p=0.035; =0.281) that demonstrated MVC for BFR (223.5±56.8 N) was less than CON (231.6±69.0 N). The men demonstrated a decrease in pre- (347.6±52.2 N) to post-exercise MVC (214.4±33.8 N; p< 0.001), but women did not (pre: 205.4±46.2 N; post: 142.8±32.2 N; p=0.084). The men did demonstrate greater pre- (p< 0.001) and post-exercise (p=0.002) MVC force than the women. For twitch force-PP, there was a significant condition x time x sex ANOVA (p=0.005, =0.438). Follow-up time x sex ANOVAs were run separately for CON and BFR. For CON, the men demonstrated a decrease in twitch force-PP from pre- (20.8±7.1 N) to post-exercise (14.9±5.1 N; p=0.033), with no difference for the women (p=0.613). For CON the men demonstrated greater twitch force-PP pre-exercise than the women (6.8±4.6 N; p< 0.001), but no difference between sexes post-exercise (women=9.6±7.6; p=0.126). For BFR, there were no pre- to post-exercise decrease in twitch force-PP force for men or women (p >0.172). The men demonstrated greater post-exercise twitch force-PP (16.8±6.6 N) than the women (7.3±3.4 N; p=0.003), with no difference in pre-exercise (men: 15.9±7.4 N; women: 10.6±7.3 N; p=0.131). CONCLUSIONS. A decrease in CON pre- to post-exercise twitch force-PP in men, but not women, indicated peripheral fatigue contributed to a greater extent to failure in men, while additional mechanisms other than peripheral fatigue contributed to task failure in women. The lack of change in pre- to post-exercise twitch force-PP for both sexes and greater post-exercise twitch force-PP for men compared to women during BFR indicates mechanisms other than peripheral indices of fatigue alone are contributing to task failure for both sexes when BFR is applied. PRACTICAL APPLICATIONS. The addition of BFR augments fatigue in both men and women, but the reasons for failure may be different between the sexes. Coaches and practitioners should be aware of these differences in fatigue between the sexes that exist between CON or BFR conditions, as changes in performance noted after BFR conditions may not accurately depict similar mechanisms of muscular failure as CON conditions.

Acknowledgements: None