Why do team sports athletes drink fluid in excess when exercising in cool conditions?

This study assessed the potential physiological and perceptual drivers of fluid intake (FI) and thirst sensation (TS) during intermittent exercise. 10 male rugby players (17 ± 1 years, stature: 179.1 ± 4.2 cm, body mass (BM): 81.9 ± 8.1 kg) participated in 6x6 min small-sided games, interspersed with 2 min rest, where FI was ad libitum during rest periods. Pre and post measurements of BM, subjective ratings (thirst, thermal comfort, thermal sensation, mouth dryness), plasma osmolality (POsm), serum sodium concentration (S[Na+]), haematocrit and haemoglobin (to calculate plasma volume change; PV) were taken. FI was measured during rest periods. BM change was -0.17 ± 0.59% and FI was 0.88 ± 0.38L. Pre to post POsm decreased (-3.1 ± 2.3 mOsm·kg−1; p = 0.002) and S[Na+] remained similar (-0.3 ± 0.7mmol·L-1, p = 0.193). ∆PV was 5.84 ± 3.65%. FI displayed a relationship with pre POsm (r = -0.640, p = 0.046), pre thermal comfort (r = 0.651; p = -0.041), ∆S[Na+] (r = 0.816, p = 0.004), and ∆PV (r = 0.740; p = 0.014). ∆TS displayed a relationship with pre mouth dryness (r = 0.861, p = 0.006) and ∆mouth dryness (r = 0.878, p = 0.004). Yet a weak positive relationship between ∆TS and FI was observed (r = 0.085, p = 0.841). These data observed in an ambient temperature of 13.6 ± 0.9̊C, suggest team sport athletes drink in excess of fluid homeostasis requirements and TS in cool conditions, however this was not influence by thermal discomfort.

http://dx.doi.org/10.1139/apnm-2016-0445