The effect of menstrual cycle on maximal breath-hold time.

This study investigated the effect of menstrual cycle phase on breath-hold time (BHT). Twelve healthy females, aged 18-30 yrs, with regular menstrual cycles, without breath-hold (BH) experience, performed a BH protocol which included eight repeated maximal efforts with face immersion in cool water separated by 2-min intervals in two different phases of menstrual cycle; early follicular (EF) phase and midluteal (ML) phase. Respiratory, cardiovascular and hematological responses were studied before, during and after BH efforts. Maximal BHT was significantly higher during ML (115.59 ±â€¯13.95 s) compared to EF (106.10 ±â€¯12.42 s) phase of the menstrual cycle. Metabolic rate and build-up of CO2 were higher (p < 0.001) in EF compared to ML phase. In conclusion, the greater BHT observed at the ML phase of the menstrual cycle may be the result of elevated levels of estrogen and progesterone during midluteal phase affecting both ventilatory response and metabolic rate.