Alterations In Performance And Perceived Fatigability In Hormonal Contraceptive Users

Exercise tolerance, characterized by an integration of neurophysiological and perceptual responses, has demonstrated contradictory profiles across the menstrual cycle. PURPOSE: This ongoing study aims to investigate the effects of endogenous and exogenous ovarian hormonal changes on determinants of exercise tolerance. METHODS: After a ramp-incremental test, combined monophasic oral contraceptive pill (OCP) and hormonal intrauterine device users (hIUD) (n = 7 in each group; 22 ± 1.2 yrs) completed two randomized visits whereby a cycling protocol at 5% below respiratory compensation point to task failure was performed. In OCP, sessions were performed in the active and inactive pill phases, randomly, and in hIUD, sessions were separated by ~14 days. Neuromuscular evaluations, including isometric knee extension maximal voluntary contraction (MVC) superimposed with electrical stimulation of the femoral nerve and transcranial magnetic stimulation of the motor cortex, were performed at baseline, every 5 min during cycling, and at task failure. Effort, pain, fatigue, and dyspnea were recorded at the same time intervals as neuromuscular evaluations. RESULTS: There was no significant difference between the OCP and IUD for all performance fatigability measures. Task duration was 43.9 ± 17.9 vs. 39.1 ± 13.2 min in the active vs. non-active pill phase in OCP and 41.5 ± 17.8 vs. 46.0 ± 19.9 min in the first vs. second visit in IUD, respectively (p = 0.128). Pre- to post-MVC decline was -14.0 vs. -21.1% in OCP and -25.9 vs. -25.6% in IUD (p = 0.374). Pre- to post-potentiated twitch decline was -32.8 vs. -34.3% in OCP and -37.8 vs. -33.6% in IUD (p = 0.526). Pre- to post-changes in voluntary activation were -6.9 vs. -3.6% in OCP and -6.6 vs. -5.6% in IUD (p = 0.307). There was no significant difference in the kinetics of effort, pain, fatigue, and dyspnea sensations across cycling tasks in the two experimental visits between OCP and IUD. CONCLUSIONS: During a warm weather race, TDEV displayed overall good agreement with a mean bias of -0.21 ± 0.48°C compared to TGI and fair agreement at race finish with a mean bias of -0.10 ± 0.6°C, therefore it is not equipped to diagnose exertional heat stroke. Continued validation and enhancement of the algorithm for TDEV in future, adequately powered studies with varying populations, environmental conditions, intensities, equipment and clothing worn, and at the upper limits of hyperthermia (i.e. >39.5°C) are needed to establish appropriate validity for use during training and competition.