Athletic performance may be compromised in extreme heat; this was relevant for the Athens and Beijing Olympics and may be for the 2014 and 2022 FIFA World cups in Brazil and Qatar respectively; under those conditions prior determination of required fluid intake is vital for athlete safety. Thompson (1954) described lower sweating rates in Bantus compared with Caucasians. The three aims of the study are: first, to determine the ethnic mix of the English Football Premiership. Second, to establish the fluid intake, sweat production and sweat evaporation during exercise in extreme heat. Third, to determine whether there are ethnic differences in the above and to establish the cardiorespiratory and other physiological factors contributing to any putative ethnic differences. Using Scout 7 software, we analysed all 270 English Football Premiership footballers in 2009; 44% players were of African origin (AO) and 56% of European origin (EO). Heart rate variability (HRV) was calculated from a five minute collection of resting ECG using bespoke frequency domain analysis software using American Heart Association guidelines (Omega Wave; Oregon USA). The ratio of Low frequency power (LF; 0.04 to 0.15 Hz) to High frequency power (HF; 0.15 to 0.40 Hz) i.e. LF/HF ratio, an index of sympatho-vagal tone balance, was calculated for all players. Mean + SD LF/HF ratio was 1.07 + 0.48 in AO, significantly lower than in EO (2.0 + 1.27; p= 0.03; unpaired t-test). Studies were performed in United Arab Emirates after four days heat acclimation, during 80 minutes training at 40 ± 2°C ambient temperature; 25 ± 8% relative humidity on 21 professional Premiership footballers from a single team with Ethics clearance. 12 were AO and 9 EO. Players could drink ad libitum throughout. AO and EO subjects exercised to a similar degree as evidenced by heart rates (Polar Electro). There was no difference between AO and EO in height, weight, body surface area, skin fold thickness, resting or average heart rate, electrocardiographically measured QT interval, echocardiographically measured cardiac chamber dimensions, left ventricular ejection fraction or maximum VO2. During exercise, fluid intake in AO ranged from 1.2- 3.0L (1.8 + 0.63L, median + SD) and in EO ranged from 0.5-1.9L (1.2 + 0.51L ; p=0.055; unpaired t-test). Sweat production in AO ranged from 1.8 – 3.9L (2.3+ 0.56L) compared with 1.3 – 2.7L in EO (2.09 + 0.48L; p = 0.09). We conclude that fluid intake during exercise in extreme heat may be up to 2.25 L/hr. There may be an increased sweat production in AO players which would confer a performance advantage to exercising in the heat and that this appears to be associated with an increased sympathetic tone, which has also been related to an increased risk of cardiac events (Tsuji H et al ,1996) .