Cerebral oxygenation declines but does not impair peak oxygen uptake during incremental cycling in women using oral contraceptives

To compare prefrontal cortex oxygenation in recreationally-active women using oral contraceptives (WomenOC; n = 8) to women with a natural menstrual cycle (WomenNC; n = 8) during incremental exercise to exhaustion.

Participants performed incremental cycling to exhaustion to determine lactate threshold 1 (LT1) and 2 (LT2) and peak oxygen uptake (VO₂peak). Prefrontal cortex oxygenation was monitored via near-infrared spectroscopy through concentration changes in oxy-haemoglobin (Δ[HbO₂]), deoxy-haemoglobin (Δ[HHb]), total-haemoglobin (Δ[tHb]) and tissue saturation index (TSI).

17β-oestradiol and progesterone were lower in WomenOC (35 ± 26; 318 ± 127 pmol·L⁻¹, respectively) than WomenNC (261 ± 156; 858 ± 541 pmol·L⁻¹, respectively). There were no differences in full blood examination results or serum nitric oxide (p > 0.05). However, WomenOC presented lower concentrations in ferric-reducing ability of plasma (− 8%; effect size; ES − 0.52 ± 0.61), bilirubin (− 32%; ES − 0.56 ± 0.62) and uric acid (− 17%; ES − 0.53 ± 0.61). Cardiopulmonary parameters were similar between groups during cycling, including VO₂peak (p = 0.99). While there was a significant effect of time on all parameters measured by near-infrared spectroscopy during incremental cycling, there was no effect of OC at LT1, LT2 or exhaustion calculated as a change from baseline (TSI; p = 0.096, Δ[HbO₂]; p = 0.143, Δ[HHb]; p = 0.085 and Δ[tHb]; p = 0.226). The change in TSI from LT1 to LT2 was significantly different between groups (WomenNC; mean difference + 2.06%, WomenOC; mean difference − 1.73%; p = 0.003).

Prefrontal tissue oxygenation declined at a lower relative exercise intensity in WomenOC as compared to WomenNC, however, this did not influence VO₂peak. The results provide the first evidence for variance in the cerebral oxygenation response to exercise, which may be associated with female sex hormones.