Core body temperature during competition in the heat: National Boys' 14s Junior Championships

To examine on-court core body temperature (T(C)) and sweat loss, as well as pre- and post-play hydration status, in elite adolescent tennis players during a national championships event in a hot climate. Eight healthy, fit, young male tennis players (mean (SD) age 13.9 (0.9) years; mass 56.0 (10.7) kg; height 169.2 (14.7) cm) were evaluated during first-round singles competition at the National Boys' 14s Junior Championships in the heat (wet-bulb globe temperature (WBGT) 29.6 (0.4) degrees C). Five of those same players were also evaluated during a same-day doubles match (WBGT 31.3 (0.5) degrees C). During doubles (4.37 (0.35) h after singles), pre-play urine specific gravity (USG) (1.025 (0.002); p = 0.06) and total sweat loss (1.9 (0.2) litres; p = 0.10) tended to be higher before and during doubles, respectively, compared to singles. However, percentage change in body mass (-0.5 (0.3) %) tended to be comparatively less (p = 0.08), even though the doubles matches were generally longer (106.6 (11.2) vs 78.8 (10.9) min; p = 0.09) and the degree minutes total was greater (p = 0.04). T(C) increased (p