Kylie Sears1, Tony Montgomery Jr.1, Alex Olmos1, Pasquale Succi2, Ethan Hill3, Haley Bergstrom2, Michael Trevino1, Taylor Dinyer-McNeely1 and Shane Hammer1

1Oklahoma State University, Stillwater, OK

2University of Kentucky, Lexington, KY

3University of Central Florida, Orlando, FL

Differences in oxygen delivery across the contraction-relaxation cycle of intermittent contractions may contribute to sex differences in exercise tolerance at matched relative intensities. Specifically, consequences of increased intramuscular pressures during contraction, including reductions in blood flow (BF), may differ between sexes resulting in sex-specific determinants of time to task failure (TTF).

PURPOSE: To determine sex differences in absolute- and %-reductions in BF during muscular contractions and relationships between BF reductions and TTF.

METHODS: Thirteen men (25 ± 4 yrs) and 13 women (22 ± 5 yrs) completed intermittent isometric trapezoidal forearm flexion at 50% maximal voluntary contraction until task failure. Doppler ultrasound was used to measure brachial artery BF during the 12-s plateau phase and 12-s relaxation phase. Sex-differences in absolute BF between phases at end-exercise were tested using ANOVA (phase × sex). Sex-differences in absolute- and %-reductions in BF at end-exercise were determined by t-tests. Linear regression was performed to identify relationships between BF reductions and performance characteristics.

RESULTS: Target torque was less in women compared to men (24 ± 5 vs. 42 ± 7 Nm; p < 0.001); however, TTF was not different between sexes (W: 425 ± 187 vs. M: 401 ± 158 s; p = 0.72). Relaxation-phase BF at end-exercise was less in women compared to men (435 ± 161 vs. 937 ± 281 mL/min; p < 0.001) but contraction-phase BF was not different (127 ± 46 vs. 190 ± 99 mL/min; p = 0.42). Absolute- and %-reductions in BF by contraction were less in women compared to men (309 ± 146 vs. 747 ± 210 mL/min and 69 ± 10 vs. 80 ± 6%, respectively; both p < 0.01) and were associated with target torque independent of sex (r = 0.78 and 0.56, respectively; both p < 0.01). Interestingly, absolute BF reduction per target torque (mL/min/Nm) and TTF were positively associated in men (r = 0.60; p = 0.031) but negatively associated in women (r = -0.61; p = 0.029).

CONCLUSION: Reductions in BF during the contraction phase of intermittent isometric contractions at matched relative intensities were sex-dependent and likely a consequence of differences in absolute torque production between men and women. However, the relationship between contraction-induced BF reductions and TTF was inverted in women compared to men.

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