Sex differences in IL-6 responses to moderate-intensity aerobic exercise are explained by cycling power output

This study characterized interleukin-6 (IL-6) and derivative-reactive oxygen metabolites (d-ROMs) responses to moderate-intensity exercise in healthy adults and assessed whether sex differences were due to workload. Fifteen males (26.5 ± 2.9 years, BMI: 23.7 ± 3.1) and 14 females (25.7 ± 2.8 years, BMI: 21.2 ± 1.8 in the menstrual phase (MP) and 21.8 ± 2.1 in the luteal phase (LP)) completed 60 min of cycling at 65 ± 5% of predicted maximal heart rate. Power output was 42.8 ± 11.8 W (MP), 44.0 ± 14.1 W (LP), and 78.8 ± 26.9 W (males) (MP vs. males and LP vs. males: p < 0.001). IL-6 and d-ROMs were measured before (Pre), immediately after (Post0), and 60 min after exercise (Post60), and group × time effects were tested using linear mixed-effects models. IL-6 showed a group × time interaction. Males had greater IL-6 responses than females at Post0 (MP vs. males: p < 0.001; LP vs. males: p < 0.05), but these differences were not significant after adjusting for power output. d-ROMs showed no significant changes over time or by group. Power output correlated with carbohydrate oxidation. These findings suggest that, at the same relative intensity, sex differences in IL-6 responses reflect workload.