Muscle blood flow is not reduced in humans during moderate exercise and heat stress

Abstract

The effect of heat stress on circulation in an exercising leg was determined using one-legged knee extension and two-legged bicycle exercise, both seated and upright. Subjects exercised for three successive 25-min periods wearing a water-perfused suit: control [CT, mean skin temperature (Tsk) = 35 degrees C], hot (H, Tsk = 38 degrees C), and cold (C, Tsk = 31 degrees C). During the heating period, esophageal temperature increased to a maximum of 37.91, 39.35, and 39.05 degrees C in the three types of exercise, respectively. There were no significant changes in pulmonary O2 uptake (VO2) throughout the entire exercise period with either one or two legs. Leg blood flow (LBF), measured in the femoral vein of one leg by thermodilution, remained unchanged between CT, H, and C periods. Venous plasma lactate concentration gradually declined over time, and no trend for an increased lactate release during the heating period was found. Similarly, femoral arteriovenous O2 difference and leg VO2 remained unchanged between the three exercise periods. Although cardiac output (acetylene rebreathing) was not significantly higher during H, there was a tendency for an increase of 1 and 2 l/min in one- and two-legged exercise, respectively, which could account for part of the increase in total skin blood flow during heating (gauged by changes in forearm blood flow). Because LBF was not reduced during exercise and heat stress in these experiments, the additional increase in skin blood flow must have been met by redistribution of blood away from vascular beds other than active skeletal muscle.

Skeletal muscle substrate metabolism during exercise: methodological considerations

“…3 and Table 1). The largest (0·3-0·4 litre/min) difference is observed when skin temperature is high (Savard et al 1988). This finding was confirmed by direct measurements of the blood flow in the saphenous vein in one subject during moderate and intense cycle exercise in a warm (40°) and a cold (17°) environment.…”

The influence of ambient temperature on power at anaerobic threshold determined based on blood lactate concentration and myoelectric signals

“…Exercising in a hot environment contributes to a higher degradation of muscle glycogen and greater blood lactate accumulation [5]. However, Savard et al [19] and Yang et al [20] have shown that during exercise in hot environment, muscle blood flow and muscle glycogen do not decrease more than under the thermo-neutral conditions. There are many reasons for trying to quantify the intensity of exercise; these including the necessity to assess the cardiovascular and pulmonary functions during workload or to evaluate the training programs for sportsmen and categorize the exercise as mild, moderate, or intense.…”

Aspectos atuais sobre aminoácidos de cadeia ramificada e exercício físico

“…Desse modo, tem sido sugerido que o estresse térmico per se pode acelerar a ocorrência da fadiga por meio da redução da função de centros motores no cérebro, alteração do recrutamento de unidades motoras ou diminuição da motivação para a atividade. A observação desses fatos, aliada ao conhecimento que ACR estão relacionados com a hipótese da fadiga central, têm acarretado em estudos que visam avaliar o efeito da suplementação com ACR sobre a performance de indivíduos submetidos a exercício de endurance em ambientes quentes (Nielsen et al, 1990;Savard et al, 1988).…”