Quantifying heat strain and its effect on intermittent sprint exercise in male games players under climatic heat stress: The Physiological Society Conference Proceedings

Heat per se(heat strain) has been suggested as a contributing factor to reduced exercise times and intermittent sprint running times while under heat stress (Morris et al. 1998), yet less is known about the effect of heat strain on intermittent sprint cycling. This investigation aimed to quantify the amount of heat strain (Physiological Strain Index, PSI; Moran et al. 1998) and its effect on peak power output (PPO)during a Cycling Intermittent Sprint Protocol in temperate (CISPtemp; 21.4±0.3°C, 62.2±2.0% relative humidity; RH;)and hot, humid conditions (CISPhot;37.1|±1.4o°C,74±2.4 %RH).Eight male games players (age, 23.3±0.8yr, mass 76.4±2.2kg, peakoxygenuptake3.8±0.1L.min-1,means±SEM)completed both CISPs, each of twenty,2min periods (10s rest,5s sprint against a resistance of 7.5% body mass and 105s active recovery at 50% of predetermined ) in a randomised order. Oxygen consumption, ratings of thermal sensation(TS),perceived exertion(RPE)and finger tip blood samples (analysed for lactate concentration) were measured in all conditions. Peak PSI was greater in CISPhot (8.2±0.2) compared to CISPtemp (7.0±0.2; P<0.01). Subjects completed the CISPtemp without any decline in PPO. In CISPhot PPO declined by sprint 10(fig 1;P<0.05) and subjects (n=5) stopped after sprint 11. Negative correlations were observed between PSI and PPO in CISPhot (r=-0.80;P<0.01) and PPO declined with a corresponding PSI value of7.3 (High). PSI positively correlated with the RPE and TS in both environments (P<0.01). There were no differences in blood lactate or oxygen consumption between environments. Decrements in PPO while under heat stress are related to greater heat strain, rather than changes in lactate concentration or oxygen cost. Observed relationships between the quantifiable PSI and the subjective RPE/TS may indicate a centrally regulated mechanism (Noakes.T.D,2004)Moran, DS et al.(1998).Am J Physiol Regulatory Integrative Comp Physiol. 275:R129-134.Morris, G et al. (1998). J Sports Sci. 16:677-686, .Noakes, T. D. (2004). J. Appl Physiol. 96:1571-1573