Response of women using oral contraception to exercise in the heat

To compare the response of long-term oral contraceptive users (WomenOC; n = 8) to naturally menstruating women (WomenNM; n = 8) at rest and during exercise in temperate (TEMP; 22 °C) and hot (HEAT; 35 °C) conditions.

Participants performed a three-stage cycling trial in each condition at 90, 135, and 180% of lactate threshold 1 (total = 52.5 min). Heart rate (HR) and core temperature (T _c) were recorded continuously, whereas blood pressure (BP), ratings of perceived exertion (RPE), blood lactate [La⁻], and skin blood flow (BF_sk) were recorded every 7.5 min.

Baseline T _c was higher in WomenOC (37.5 ± 0.2, 37.6 ± 0.3 °C) than WomenNM (37.2 ± 0.2, 37.0 ± 0.4 °C) before the TEMP (p = 0.03) and HEAT (p < 0.01) trials, respectively. This difference remained for 22.5 min into both trials (p ≤ 0.05), after which time no between-group differences were found (p > 0.05). BF_sk measured in WomenNM plateaued from 7.5 min in the HEAT, whereas BF_sk measured in WomenOC increased for 15.0 min (p = 0.02) before plateauing. There were no between-group differences in HR, BP, or blood [La⁻] before or throughout either trial (p > 0.05). WomenOC had higher (p ≤ 0.04) RPE values than WomenNM in the HEAT, reporting 8 ± 1 and 6 ± 2 at the end of Stage 3, respectively.

WomenOC concluded both trials with a comparable T _c to WomenNM, but had a prolonged BF_sk response and elevated RPE in the HEAT. Changes to BF_sk and RPE observed in women using OC may have implications for exercise tolerance in hot conditions.