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

Abstract

IntroductionInvestigate 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 MethodsTen, moderately trained, females (Mean [SD]; age 22.6 [2.7] y; stature 165.3 [6.2] cm; body mass 61.5 [8.7] kg; V.⁢O2⁢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.ResultsPre (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); T¯s⁢k (−0.50; −0.90 to −0.10°C; d = 0.80); and T¯b (−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.DiscussionShort-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.

Effectiveness of short-term isothermic-heat acclimation (4 days) on physical performance in moderately trained males

“…Upon achieving this target, participants ceased exercising and were seated for the remainder of the session–unless T re fell below 38.5°C then light exercise was prescribed. This protocol is identical to previous work conducted by Garrett and colleagues [ 5 , 10 , 35 , 36 ] but over 4 d HA.…”

“…Considering the duration and number of daily exposures, it may be worth noting the total exposure time versus the time spent above 38.5°C T re . A T re of 38.5°C has been routinely used in controlled hyperthermia studies and is widely viewed as the threshold for adaptive response [ 2 , 35 , 49 , 54 , 55 ]. Therefore, it would seem appropriate to record the time spent above 38.5°C when comparing between studies.…”

“…The fundamental component of using the controlled hyperthermia technique is that participants experience the same thermal load, as was the case in the current study—experiencing mild hypohydration of ~1.3% BM in both the pre- and post-intervention trials ( Table 1 ). Blood parameters during acclimation ( Table 3 ) indicates a meaningful change in [Na + ] p −which is responsible for aiding fluid retention [ 35 ]–on day one but not day four despite an increase in resting [aldo] p . Post-exercise [aldo] p increased significantly from resting concentrations on day four.…”

“…Utilising the controlled hyperthermia methodology protocols vary in exercise mode, exposure duration, exposure intensity, and the number of repeated bouts. Heat acclimation adaptations are achieved within 4–7 d [ 34 ] and a 5 d protocol is commonly used [ 2 , 5 , 10 , 28 , 33 , 35 – 37 ]. Limited evidence exists following 4 d of heat exposure.…”

Short-term heat acclimation preserves knee extensor torque but does not improve 20 km self-paced cycling performance in the heat

“…In comparison to traditional HA protocols, shortterm approaches (e.g., ≤ 7 days) are proposed as a practical, time-efficient alternative for athletes when tapering before competition (Racinais and Périard 2020), while still partially inducing beneficial physiological adaptations (Garrett et al 2011;Chalmers et al 2014;Daanen et al 2018). These adaptions are also present in moderately trained and recreational athletes who undertake HA training (Garrett et al 2009(Garrett et al , 2011(Garrett et al , 2019Ashley et al 2015).…”