Effectiveness of short term heat acclimation on intermittent sprint performance with moderately trained females controlling for menstrual cycle phase

Abstract

Introduction: Investigate the effectiveness of short-term heat acclimation (STHA), over 5-days (permissive dehydration), on an intermittent sprint exercise protocol (HST) with females. Controlling for menstrual cycle phase. Materials and Methods: Ten, moderately trained, females (Mean [SD]; age 22.6 [2.7] y; stature 165.3 [6.2] cm; body mass 61.5 [8.7] kg; VO˙ 2 peak 43.9 [8.6] mL·kg−1 ·min−1 ) participated. The HST (31.0◦C; 50%RH) was 9 × 5 min (45-min) of intermittent exercise, based on exercise intensities of female soccer players, using a motorized treadmill and Wattbike. Participants completed HST1 vs. HST2 as a control (C) trial. Followed by 90 min, STHA (no fluid intake), for five consecutive days in 39.5◦C; 60%RH, using controlled-hyperthermia (∼rectal temperature [Tre] 38.5◦C). The HST3 occurred within 1 week after STHA. The HST2 vs HST3 trials were in the luteal phase, using self-reported menstrual questionnaire and plasma 17β-estradiol. Results: Pre (HST2) vs post (HST3) STHA there was a reduction at 45-min in Tre by 0.20◦C (95%CI −0.30 to −0.10◦C; d = 0.77); Tsk (−0.50; −0.90 to −0.10◦C; d = 0.80); and Tb (−0.25; −0.35 to −0.15◦C; d = 0.92). Cardiac frequency reduced at 45-min (−8; −16 to −1 b·min−1 ; d = 1.11) and %PV increased (7.0; −0.4 to 14.5%: d = 1.27). Mean power output increased across all nine maximal sprints by 56W (−26 to 139W; d = 0.69; n = 9). There was limited difference (P > 0.05) for these measures in HST1 vs HST2 C trial. Discussion: Short-term heat acclimation (5-days) using controlled-hyperthermia, leads to physiological adaptation during intermittent exercise in the heat, in moderately trained females when controlling for menstrual cycle phase.