Author(s): KEEFE, M., DUNN, R., SEKIGUCHI, Y., Institution: TEXAS TECH UNIVERSITY, Country: UNITED STATES, Abstract-ID: 1479

INTRODUCTION:
Training and competing in the heat negatively impact athlete performance and health. Heat acclimation (HA) involves repeated heat exposures that many endurance athletes use to optimize performance and safety when competing in the heat. Although HA has been shown to improve endurance performance in the heat, contention remains whether it may confer these adaptations to a cool environment. Thus, the purpose of this study was to investigate physiological and performance adaptations in a cool environment following HA in endurance athletes.
METHODS:
Seven high-level endurance runners (6 females [age: 20±2 years; body mass: 62.05±5.81 kg; maximal oxygen uptake [VO2max], 61.52±7.21 mL·kg-1·min-1], 1 male [age, 19 years; body mass, 66.80 kg; VO2max, 79.60 mL·kg-1·min-1]) participated in this pilot study. As a baseline assessment, participants completed a VO2max test, followed by an 8-kilometer time-trial (TT) in cool conditions (ambient temperate [Tamb], 11°C; relative humidity [RH], 40%). Following this, participants completed a 7-day training protocol consisting of 60-minutes running at 50% velocity at VO2max in either a thermoneutral (n = 3; Tamb, 22°C; RH, 40%) or hot condition (n = 4; Tamb, 40°C; RH, 35%). Physiological variables (i.e., core temperature [Tc], sweat rate [SR], plasma volume [PV]) were assessed on days 1 and 7 to determine HA adaptations. A post-testing visit was conducted to determine performance (VO2max, lactate threshold [LT], TT) changes. A two-way repeated measures ANOVA was conducted to assess physiological and performance changes from pre- to post-testing for performance variables, and from days 1 to 7 for physiological variables, between conditions. Cohen’s d classification of effect sizes was calculated to determine small (0.20-0.50), medium (0.50-0.80), and large (>0.80) effects.
RESULTS:
No significant differences were identified for physiological variables (i.e., Tc, SR, and PV) between days 1 and 7 in both conditions (ps > 0.05), however, large effects for SR (d = 0.95), and small effect sizes for Tc (d = 0.20) and PV (d = 0.18) were observed in the heat condition. The thermoneutral condition experienced small effect sizes for Tc and SR (d = 0.06-0.37), and a medium effect size for PV (d = 0.51). Similarly, there were no significant improvements in performance metrics (i.e., VO2max, LT, and TT) from pre- to post-training between conditions (ps > 0.05). In the heat condition, LT and VO2max demonstrated medium effect sizes (d = 0.51-0.63), but TT (d = 0.08) resulted in a small effect size. For the thermoneutral condition, LT, VO2max, and TT demonstrated small effect sizes (d = 0.00-0.19).
CONCLUSION:
The present findings indicate that heat acclimation may procure the necessary adaptations to improve endurance performance in cool temperatures. Caution should be taken when interpreting these findings due to the nature of pilot data analyzed. This research was supported by a World Athletics Research Grant from the American College of Sports Medicine.