The critical level of water deficit causing a decrease in human exercise performance: a practical field study

Abstract

To analyse the critical level of water deficit which causes a decrease in aerobic and anaerobic exercise performance, a step test score (STS) and 10 s maximal anaerobic power (MAP) output during cycling exercise were measured in two experiments (Ex-1, n=7, and Ex-2, n=9), before and after baseball practice, using subjects who played regularly. The measurements in both Ex-1 and Ex-2 were repeated under four conditions of fluid ingestion (FI) (FI of 80%, 60%, 40%, and 20% of the total sweat loss) on hot summer days. The subjects were allowed free access to a sports beverage, maintained at 10-15 degrees C, within any given FI condition during the exercise. The [mean (SEM)] duration of the exercise and the environmental conditions (wet bulb globe temperature) were similar between Ex-1 [3.52 (0.14) h and 29.2 (0.6) degrees C, respectively] and Ex-2 [3.82 (0.12) h and 29.2 (0.4) degrees C, respectively]. In both Ex-1 and Ex-2, the loss of body mass (Delta m(b)) increased significantly as FI decreased. In Ex-1, the STS significantly decreased ( P<0.05) at values of delta m(b) in excess of 2.4 (0.2)% (40%FI). In Ex-2, the MAP remained unchanged at values of delta m(b) up to 2.5 (0.3)% (40%FI), while the MAP significantly decreased ( P<0.05) at values of delta m(b) of 3.9 (0.2)% (20%FI). These results suggest that there is a critical level of water deficit at which a decrease in aerobic and anaerobic performance occurs, and that aerobic performance may be more adversely influenced by dehydration than anaerobic power output during exercise-induced dehydration.

Can firefighter instructors perform a simulated rescue after a live fire training exercise?

“…From the literature pertaining to sports performance such a low level of dehydration is unlikely to affect either thermoregulation or performance (Cheuvront and Haymes 2001;Yoshida et al 2002). However studies on firefighters working in the heat have shown a 15% reduction in plasma volume after only three 7-min bouts of firefighting tasks (Smith et al 2001b).…”

Rehydration with drinks differing in sodium concentration and recovery from moderate exercise-induced hypohydration in man

“…He concluded that hypohydration of 2% or greater may be tolerated without significant effects on performance when environmental conditions are moderate (\25°C) (Robinson et al 1995;McConell et al 1997;Backx et al 2003), but that hypohydration of approximately 2% or more of body mass impairs performance and increases the risk of heat injury when environmental temperatures are high ([30°C) (Walsh et al 1994;Below et al 1995;Yoshida et al 2002). The critical point at which a performance reduction occurs is likely to be influenced by many factors, including the rate at which hypohydration is induced, the subject's core temperature and the exercise mode: there may be some advantage of a small reduction in body mass when this must be supported or carried, as in running (Sawka and Noakes 2007).…”

A wearable electrochemical sensor for the real-time measurement of sweat sodium concentration

“…Dehydration for example can manifest itself as an increased sodium concentrations in sweat during exercise, so the possibility of monitoring this quantitatively in real-time is an appealing prospect 1 . Currently, for studies involving athletic performance, instead of directly analysing specific electrolyte concentrations, available fluid volumes are usually inferred only from body weight loss and urine output volumes over a set period of exercise, with electrolyte concentrations only measured separately and retrospectively [2][3][4][5] .…”