Fluid Replacement Strategy during a 27-Km Trail Run in Hot and Humid Conditions

Abstract

We evaluated the effects of the fluid replacement strategy on core temperature, heart rate and urine osmolality during a 27-km trail run in tropical climate. 20 well-trained runners completed a 27-km trail race in tropical conditions. They were acclimatized to these conditions. Heart rate was monitored every 5 s, while core temperature and perceived thermal and comfort sensations were recorded before, at the 11(th) km, and just after the end of the race. Water intake, urine osmolality and body mass were measured before and after the race. Core temperature and the scores of perceived thermal and comfort sensations were significantly higher at the 11(th) km and at the end of the race compared to before the race, but not at the 11(th) km compared to the end of the race [corrected]. No participant exhibited dehydration as assessed by urine osmolality. The less the trail runners weighed, the greater the heat retention was. The less hot they felt at the end of the race, the more they lost water, and the better the performance was. The fastest runners were able to tolerate a greater variation in core temperature between the beginning and the end of the trail race with lower water intake.

A Pilot Study on How Do Elite Surfski Padllers Manage Their Effort and Hydration Pattern in the Heat

“…Some studies demonstrated that aerobically fit individuals attained significantly greater end-point temperatures than less-aerobically fit ones [ 19 ]. The fact that highly fit runners sustain high core temperatures throughout prolonged competitions [ 20 , 21 ] is in accordance with the present results showing that high performance is related to high core temperature. In this context, it has also been demonstrated that the increase in core temperature is unlikely to be a primary signal to start the anticipatory process [ 22 ].…”

“…The mean increase in T° C was only 0.45°C · hr -1 which is very relatively low regarding the environmental conditions and the athletes’ stature. Indeed, although these results agree with those noted for similar time spent running in tropical climate [ 21 ], it has been demonstrated that bigger athletes increased more their core temperature that smaller ones [ 23 ] and the present kayakers were definitively bigger (i.e., a mean of 84.5 kg) than the runners described in the study of Baillot et al [ 21 ]. We thus would have expected higher heat production and consecutive heat accumulation in relation to exercising in hot and humid environment.…”

“…When considered with the results concerning both the performance and the HR, one can infer from these finding that the kayakers having the highest intensities were able to turn in the best performances without a lot of hydration. Similar results have been noted during running and long-duration exercises, with the fastest finishers in endurance events often being the most dehydrated [ 21 ], confirming the observed fact that elite endurance athletes do not drink very much during exercise [ 28 ]. The most likely explanation is that the best kayakers, being the most trained, were able to paddle at higher intensities while drinking less water and supporting higher T° C increases.…”

“…The correlations between change in T° C and body mass loss (TBWL and TBWL · h -1 ) agree with theses explanations. Indeed, when running in tropical climate, because high humidity do not permit evapotranspiration, greater TBWL and T° C increases are usually observed in better runners [ 21 ]. In the present study, the opposite was observed with the better kayakers being effectively those with the greater T° C increase but the lowest T° C increase being correlated with higher body mass loss and TBWL; we could therefore make the hypothezis that the loss in body water was concomitant with an efficient evapotranspiration related to air convection [ 24 ] and/or ocean water cooling.…”

Self-hydration and thermoregulatory processes of average-level paddlers during international surfski events in a tropical climate

“…Taken together, these findings reinforce the view that ad libitum hydration is enough for endurance exercise in a hot environment [17, 21, 22, 23]. These results could be surprising if we consider that average-range athletes normally drink at a higher rate than high-level or more trained ones [24, 25]. In a recent study, Hue et al [9] noted quite pronounced differences between internationally ranked competitors who drank a mean 1.1 L, corresponding to 0.35 L · h −1 , and three nationally ranked competitors who drank a mean 2.2 L, corresponding to 0.80 L · h −1 .…”