Greater chance of high core temperatures with modified pacing strategy during team sport in the heat

Objectives: To measure the activity profile, hydration status and core temperature of elite team sport athletes during matches in hot and cool conditions. Design: Thirty-five professional Australian footballers (age 25.9 +/- 3.5 yrs; height 188.4 +/- 7.8 cm; body mass 90.6 +/- 8.8 kg), gave informed consent to participate in this study. Core temperature (T-c), hydration and running performance were compared in eight hot and eight cool matches classified via a rating of the risk of heat illness from the Wet Bulb Globe Temperature (WBGT). Methods: Core temperature was measured via an ingestible sensor before matches and after each quarter and player movement was recorded by 5 Hz GPS and expressed per period of the match (rotation), for distance; high-intensity running (HIR, 4.17-10.00 m s(-1)), sprinting (>4.17 m s(-1)) and maximal accelerations (2.78-10.00 m s(-2)). All data was compared for hot and cool matches and the magnitude of effects was analysed with the effect size (ES) statistic. Results: Core temperature was elevated from rest at all time-points during matches (37.3-39.4 degrees C), with small additional elevations after the first and third quarters in hot matches (ES: 0.39 +/- 0.40 and 0.37 +/- 0.42 respectively). In hot matches 12 players had T-c > 40 degrees C but only one in cool matches. Total distance was reduced in the latter parts of each half (-6.5%, -0.49 +/- 0.58; and -6.7%, -0.57 +/- 0.59), yet the high intensity tasks of sprinting and accelerating were preserved. Conclusions: Players tolerated core temperatures up to 40.5 degrees C during hot matches but reduced the volume of running undertaken, thus preserving the ability to undertake high intensity activities. (C) 2013 Published by Elsevier Ltd on behalf of Sports Medicine Australia.