No sex differences in systemic metabolic responses to acute sprint interval training performed after an oral 75-g glucose load in adults with excess adiposity.

Background & aims: Research exploring sex-based variations in responses to acute sprint interval training (SIT) remains limited. This study aimed to examine the impact of biological sex on the systemic metabolic response to SIT. We hypothesized that acute metabolic responses to SIT would differ between males and females.

Methods: Sedentary adults (15 males; 14 females) with excess adiposity (defined as body fat > 30%) were matched for age (32.8 ± 7.5 vs. 29.5 ± 6.5 years) and body fat mass (33.0 ± 6.9 vs. 33.2 ± 6.8%). Following a 75-g glucose load, participants were randomly allocated to either a control (resting) or SIT trial (8 × 30 s of "all-out" cycling at a resistance of 0.075% W kg^-1 of muscle mass, interspersed with 1 min of recovery). Parameters assessed included respiratory quotient (RQ), resting energy expenditure (REE), substrate utilization rates (fat and carbohydrate), total energy output, and blood lactate and glucose levels. These were collected during fasting and at 60, 120, and 240 minutes post-glucose load, with the area under the curve (AUC) calculated for both trials.

Results: An interaction was observed between sex × time (P = 0.012) and trial (P < 0.001) for RQ over time; however, there was no significant interaction between sex and trial (P = 0.818). Males exhibited higher mean REE values than females in both conditions. Nevertheless, AUC analysis showed no significant interaction between sex and trial (P = 0.562). A significant trial × time relationship was found for fat and carbohydrate percentage contributions (P < 0.001). Post-SIT, AUCs for fat contribution (g min^-1 and mg kg^-1 min^-1) to energy expenditure increased in both sexes compared with resting (P < 0.05), with differences noted among trials over time (P < 0.001). Blood lactate levels also increased similarly post-SIT in both sexes (P < 0.05), without a significant sex × trial interaction (AUC, P = 0.798).

Conclusions: These data demonstrate that exercise differed between the sexes and did not support the premise that acute metabolic responses to SIT would vary between males and females.