The influence of biological sex and fitness status on markers of recovery optimisation in response to prolonged high intensity interval exercise

This study aimed to characterise recovery outcomes and repeated performance following 2h high-intensity interval training (HIIT) exercise, followed by consumption of 1.2g/kg body mass (BM) and 0.4g/kgBM of carbohydrate and protein, respectively, between biological sex and fitness status categories. Venous blood samples, muscle biopsies, BM, body water, and breath samples were collected, and gastrointestinal symptoms (GIS) were measured, pre-exercise, and throughout 4h recovery. The following morning, participants returned to assess performance outcomes. Significantly greater body water losses were experienced by high (BM loss: 2.3%) vs. moderate fitness athletes (1.8%; P=0.009), but there were no differences between sexes (1.9%). Intestinal injury, carbohydrate malabsorption, and GIS occurred amongst all groups, with no differences. Phosphorylation of mTOR (P<0.001) and Akt (P=0.031), but not rpS6, increased from 0-2 h recovery in both fitness groups. Greater overall phosphorylation of GSK-3β was observed amongst high fitness (P=0.033). There were no group differences for glucose, insulin, cortisol, leukocyte or cytokine markers. A decline in neutrophil functional responses (36%) occurred for all groups. The following day, rates of carbohydrate oxidation were greater amongst males at all intensities. Rates of fat oxidation rates were greater at 50% and 60% V̇O2max, and carbohydrate oxidation were greater at 70% and 80% V̇O2max amongst high compared to moderate fitness athletes. Absolute performance was greater amongst high vs. moderate fitness; however, there were no differences in relative performance between groups. Recovery optimisation markers following a 2h HIIT exercise protocol and consumption of carbohydrate and protein at 1.2g/kgBM and 0.4g/kgBM, respectively, are similarly achieved by male and female athletes of moderate and high fitness status. Registration: This sub-group analysis was part of a larger study that was prospectively registered with ANZCTR (reference number 375090).