Comparative Responses of Self-Regulated Exercise, Thermoregulation, and Neuromuscular Function to Monophasic Oral...

This study investigated the effect of monophasic oral contraceptive (OC) use on self-paced cycling performance, thermoregulation, and skeletal muscle strength and contractile properties in healthy women. Eight physically active women performed 30 min fixed intensity cycling at 50% W_max, followed by a 30 min self-paced time trial (TT) with each section interspersed with a 30 s maximal sprint at 9, 19, and 29 min. The tests were conducted in different ambient conditions corresponding to either baseline day 1 (20°C, BASE), day 8 (20°C COOL), or day 18 (32°C WARM) of 1 month pill cycle. Core (T_c) and skin (T_sk) temperatures, heart rate, perceptual, neuromuscular responses, and serum cortisol (CORT) were measured multiple times throughout the trials and postexercise. Time trial performance remained unchanged across conditions (range 10.9-11.1 km) although T_c was elevated in WARM in the final 15 min of self-paced exercise, reaching 38.5°C (p < 0.05). CORT was increased from preexercise, whereas lactate increased in all conditions (p < 0.05). Peak force was significantly reduced from pre (439 ± 95 and 429 ± 121 N) to postexercise (345 ± 91 and 361 ± 94 N) for BASE and WARM, respectively, (p < 0.05). Twitch contractile duration declined (∼14%; p < 0.05) in all conditions along with time to peak force (∼17%, p < 0.05) in BASE and WARM. We conclude that OC use does not affect self-paced cycling performance across ambient conditions with no detrimental alteration in neuromuscular performance across the menstrual cycle.