Collegiate soccer players consistently underestimate practice sweat losses regardless of practice sweat loss volume

Soccer play in hot environments can result in major fluid deficit. If competitors are unsure of their sweat losses, accurate fluid intake needs during and between training bouts cannot be established. This study evaluated sweat loss estimation accuracy among collegiate male soccer players (n = 17) following three, 90-minute practice sessions in the heat. Data were collected during the last week of pre-season training during a morning (P1; wet bulb globe temperature (WBGT) = 31.2 degrees C) and same day afternoon (P2; WBGT = 26.9 degrees C) practice. The third estimation took place after a regular season morning practice (P3; WBGT = 31.5 degrees C) the following week. Change in nude body mass, with adjustment for fluid intake and urine output, from pre- to post-practice was assessed to determine sweat loss volume. After each practice participants estimated their sweat loss volume by filling cups with a volume of water equivalent to the volume of sweat they believed they lost during the practice session. Sweat losses differed (p < 0.05) among all 3 practices (P1 2.181 +/- 0.693; P2 1.706 +/- 0.474; P 3.360 +/- 0.956 L). Estimated sweat loss volume was less (p < 0.001) than actual sweat losses for P1 (0.804 +/- 0.329 L; 40.2 +/- 21.5%), P2 (0.672 +/- 0.324 L; 40.1 +/- 19.9%) and P3 (1.076 +/- 0.489 L; 31.8 +/- 11.6%), but there were no differences in percentage accuracy. Players estimations of sweat loss trended up and downward with actual sweat losses, but players greatly and consistently underestimated sweat losses. Visual depiction of sweat loss volume could potentially increase awareness of between training bout fluid intake needs of soccer players training in hot conditions.