Impact Of Fluctuating Sex Hormones On Heart Rate, Perceived Effort, And Blood Lactate During Heavy And Severe Domain Exercise

PURPOSE: Investigate the impact of sex hormone profile on measures of cardiovascular, perceptual, and metabolic strain in the heavy and severe exercise intensity domains. METHODS: Twelve endurance trained women (female assigned at birth; 9 IUD users & 3 naturally cycling; Age: 29 ± 7 years) completed six visits. Maximal oxygen uptake and gas exchange parameters were determined via graded exercise test on a cycle ergometer. Participants completed four weekly cycling protocols consisting of four, 4-minute stages spanning intensity domains, including the intensity associated with the predicted heavy - severe domain boundary. Serum sex hormone concentration for estradiol and progesterone was determined at the beginning of each visit. Menstrual cycle phase did not dictate visit order. Heart rate (HR) and rating of perceived effort (RPE) were measured during the last minute of each stage. Blood lactate [BLa] was measured via finger prick immediately following each stage. For analysis, visits were ordered beginning with the lowest hormone concentration (early follicular) visit first, followed by remaining visits in sequential order. Two-way repeated measures ANOVA determined differences across visits. Relationships between hormone concentration and HR, RPE, and [BLa] were analyzed via linear mixed models. RESULTS: As expected, HR, RPE, and [BLa] increased with exercise intensity (P < 0.001). Neither HR, RPE, nor [BLa] differed across the four visits (HR: P = 0.748; RPE: P = 0.216; and [BLa]: P = 0.150). HR and [BLa] were not impacted by concentration of estradiol (P = 0.647 and P = 0.622, respectively) or progesterone (P = 0.747 and P = 0.621, respectively). RPE was positively corelated with progesterone concentration (P = 0.002) but not with estradiol concentration (P = 0.431). CONCLUSIONS: These data suggest that fluctuations in sex hormone concentration do not impact measures of cardiovascular and metabolic strain during exercise in the heavy and severe domains. However, progesterone concentration appears to negatively impact perceived exertion. Supported by: Wu Tsai Human Performance Alliance at the University of Oregon