Muscle blood flow and muscle metabolism during exercise and heat stress

Abstract

The effect of heat stress on blood flow and metabolism in an exercising leg was studied in seven subjects walking uphill (12-17%) at 5 km/h on a treadmill for 90 min or until exhaustion. The first 30 min of exercise were performed in a cool environment (18-21 degrees C); then subjects moved to an adjacent room at 40 degrees C and continued to exercise at the same speed and inclination for a further 60 min or to exhaustion, whichever occurred first. The rate of O2 consumption, 2.6 l/min (1.8-3.3) (average from cool and hot conditions), corresponded to 55-77% of their individual maximums. In the cool environment a steady state was reached at 30 min. When the subjects were shifted to the hot room, the core temperature and heart rate started to rise and reached values greater than 39 degrees C and near-maximal values, respectively, at the termination of the exercise. The leg blood flow (thermodilution method), femoral arteriovenous O2 difference, and consequently leg O2 consumption were unchanged in the hot compared with the cool condition. There was no increase in release of lactate and no reduction in glucose and free net fatty acid uptake in the exercising leg in the heat. Furthermore, the rate of glycogen utilization in the gastrocnemius muscle was not elevated in the hot environment. There was a tendency for cardiac output to increase in the heat (mean 15.2 to 18.4 l/min), which may have contributed to the increase in skin circulation, together with a possible further reduction in flow to other vascular beds, because muscle blood flow was not reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

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).…”

Effect of the menstrual cycle on performance of intermittent, high-intensity shuttle running in a hot environment

“…A high deep body temperature has been suggested to be a limiting factor in exercise performance in the heat (Nielsen et al 1990(Nielsen et al , 1993Gonzalez-Alonso et al 1999). If during the luteal phase or taking oral contraceptives, a higher deep body temperature is observed during exercise, this may decrease the time to exhaustion.…”

Effect of Temperature on Muscle Metabolism During Submaximal Exercise in Humans

“…It is apparent from these results, therefore, that the augmented glycogen utilization in HL relative to CL was not secondary to changes in the adenine nucleotide pool or free inorganic phosphate (Pé) concentrations. An increased plasma adrenaline concentration has been observed during exercise and heat stress (Nielsen et al 1990;Febbraio et al 1994a;Hargreaves et al 1996a) which may partly account for the enhanced muscle glycogen utilization under such conditions (Febbraio et al 1998). However, since in the present study both legs were exposed to the same plasma adrenaline level and core temperature, this could not account for the observed difference in muscle glycogen utilization between HL and CL.…”