AUTHOR=Garrett Andrew T. , Dodd Edward , Biddlecombe Victoria , Gleadall-Siddall Damien , Burke Rachel , Shaw Jake , Bray James , Jones Huw , Abt Grant , Gritt Jarrod 

TITLE=Effectiveness of Short-Term Heat Acclimation on Intermittent Sprint Performance With Moderately Trained Females Controlling for Menstrual Cycle Phase

JOURNAL=Frontiers in Physiology

VOLUME=Volume 10 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.01458

DOI=10.3389/fphys.2019.01458

ISSN=1664-042X

ABSTRACT=<sec><title>Introduction</title><p>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.</p></sec><sec><title>Materials and Methods</title><p>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; <inline-formula><mml:math id="INEQ1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>.</mml:mo></mml:mover><mml:mo>⁢</mml:mo><mml:msub><mml:mtext>O</mml:mtext><mml:mrow><mml:mpadded width="+2.8pt"><mml:mn>2</mml:mn></mml:mpadded><mml:mo>⁢</mml:mo><mml:mi>peak</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula> 43.9 [8.6] mL⋅kg<sup>–1</sup>⋅min<sup>–1</sup>) 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 [T<sub>re</sub>] 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.</p></sec><sec><title>Results</title><p>Pre (HST2) vs post (HST3) STHA there was a reduction at 45-min in <italic>T</italic><sub><italic>re</italic></sub> by 0.20°C (95%CI −0.30 to −0.10°C; <italic>d</italic> = 0.77); <inline-formula><mml:math id="INEQ7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mover accent="true"><mml:mi>T</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mrow><mml:mi>s</mml:mi><mml:mo>⁢</mml:mo><mml:mi>k</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> (−0.50; −0.90 to −0.10°C; <italic>d</italic> = 0.80); and <inline-formula><mml:math id="INEQ9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mover accent="true"><mml:mi>T</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mi>b</mml:mi></mml:msub></mml:math></inline-formula> (−0.25; −0.35 to −0.15°C; <italic>d</italic> = 0.92). Cardiac frequency reduced at 45-min (−8; −16 to −1 b⋅min<sup>–1</sup>; <italic>d</italic> = 1.11) and %PV increased (7.0; −0.4 to 14.5%: <italic>d</italic> = 1.27). Mean power output increased across all nine maximal sprints by 56W (−26 to 139W; <italic>d</italic> = 0.69; n = 9). There was limited difference (<italic>P</italic> &gt; 0.05) for these measures in HST1 vs HST2 C trial.</p></sec><sec><title>Discussion</title><p>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.</p></sec>