Influence of ambient temperature on plasma ammonia and lactate accumulation during prolonged submaximal and self-paced running

Abstract

This study examined the effects of heat stress on the accumulation of plasma ammonia, lactate, and urate during prolonged running. Nine highly trained endurance runners completed two running trials in a counterbalanced fashion in cool (15 degrees C) and in hot (35 degrees C) humid (60% relative humidity) conditions. Subjects ran on a motorised treadmill at 70% of peak treadmill running speed for 30 min (submaximal) followed by a self-paced 8-km performance run. Blood was drawn at pre-exercise, end-submaximal and end-performance run and analysed for plasma ammonia, lactate, and urate. Four subjects failed to complete the performance run in the heat and the performance times for the rest of the subjects was increased from 27.3 (0.6) min in cool conditions to 31.3 (1.2) min in hot conditions (P < 0.05). The end-performance rectal temperature was 38.6 (0.1) and 39.2 (0.1) degrees C (P<0.05) in cool and hot conditions, respectively. Differences in plasma lactate at the end of submaximal running were not significant. However, at the end of performance runs lactate was 6.0 (0.9) m mol x l(-1) in cool and 3.1 (0.5) mmol x l(-1) in hot conditions, values that were significantly different (P<0.05). Plasma ammonia increased from pre-exercise to approximately equal to 59 micromol x l(-1) at the end-submaximal runs for both coditions and further at the end of performance runs to 108.5 (11) micromol x l(-1) (P<0.05) in hot but not in cool conditions. Plasma urate increased from pre-exercise to 311.2 (25.9) micromol x l(-1) at end-submaximal runs and to approximately equal to 320.4 micromol x l(-1) at end-performance runs in hot and cool environments. The findings that plasma urate accumulation was similar at the completion of running in both conditions, while ammonia was significantly augmented in hot conditions compared with cool, suggest that ammonia accumulation during heat stress exercise might be derived from sources other than purine catabolism.

Influence of environmental temperature on exercise-induced inspiratory muscle fatigue

“…The finding of a significant decrease in exercise performance is consistent with previous studies using constant-load cycling to exhaustion (Febbraio et al 1996b) and self-paced treadmill running (Marino et al 2001). We believe it is unlikely that the decrease in time-trial performance observed in the present study was due to between-trial differences in participant motivation.…”

The limitations of the constant load and self-paced exercise models of exercise physiology

“…Thus, constant load exercise is indeed useful when the measurement of the sensitivity of a physiological response is of primary interest. However, in self-regulated exercise, plasma lactate accumulation is lower in heat stress compared with cool conditions, because the exercise intensity is internally regulated rather than being externally driven 39 .…”

Effects of human head hair on performance and thermoregulatory responses during 10-km outdoor running in healthy men

“…Considering the type of exercise, self-paced exercise in the heat permits to evaluate the responses to exercise through the interaction of performance regulation mechanisms with the environment without the dissociation of one or more fatigue variables, as established for fixedintensity exercise 4,15,25 . Therefore, minor physiological changes may not be sufficient to elicit a higher exercise intensity during self-paced exercise 14,15 .…”

“…Key words: Body temperature regulation; Hair; Running; Solar radiation; Velocity.. (29,5 ± 3,7 anos, 174,9 ± 4,3 [3][4] , and heat storage 5 . Outdoor physical activity, especially in hot environments, may increase the physiological strain imposed on the human body due to the solar radiation.…”