Alyssa Olenick, Regis Pearson, Nathan Jenkins. University of Georgia, Athens, GA.

BACKGROUND: The menstrual cycle may impact metabolic responses to exercise such as blood lactate, with findings indicating elevated exercise blood lactate concentrations in the follicular phase. However, no studies have examined blood lactate during high-intensity interval exercise (HIIE) across the menstrual cycle. METHODS: We explored the impact of the menstrual cycle phase in 8 young, healthy, active women (24.4±2.4 yrs; 167.0±6.3cm; 66.8±11.7kg; 29.5±3.7% BF; VO2peak: 37.5±3.1 ml/kg/min) experiencing a regular menstrual cycle (n=5) or using oral contraceptives (OC) (n=3). Participants completed a baseline and two identical counterbalanced HIIE sessions. All exercise was performed on an electrically-braked cycle ergometer. One HIIE session took place in the week following the onset of the menstrual cycle or non-active OC days 2-5 during the follicular phase (FP). The other took place ~6-8 days following urine ovulation or days 20-23 of active OC pills during the luteal phase (LP). HIIT sessions were 4x4 min intervals performed at the power output corresponding to 50% of the difference between the ventilatory threshold and VO2peak separated, with 3 min of unloaded cycling (0W) as recovery between intervals. Blood lactate was assessed via finger stick across all exercise intervals, during rest periods between intervals, and at 5, 10 and 15 minutes post-exercise. RESULTS: Blood lactate was significantly greater during the FP than the LP during rest interval 1 (FP: 7.1±1.8, LP: 5.9±1.3; p=0.014) and rest interval 3 (FP: 8.4±2.2; LP: 7.0±1.9; p=0.045). Lactate trended greater in the FP during high 2 (8.1±2.4; LP: 7.2±1.7; p=0.074) and recovery at 15 minutes (FP: 4.6±1.5; LP: 4.1±1.1; p=0.076). Area under the blood Lactate curve (AUC) was not different between phases (FP: 280.4±116, LP: 266.7±81.7, p=0.598). CONCLUSION: Our results reflect elevated blood lactate during the follicular phase during HIIE, especially during recovery periods between intervals. These results suggest that intra-workout recovery during HIIE may vary across the menstrual cycle.

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