RESUMO

Evidence indicates that aerobic performance is degraded either by environmental heat stress or sleep deprivation. However, whether these conditions interact to produce more significant performance impairment deserves further investigation. Therefore, this study investigated the effects of experimental sleep deprivation (24 h or 96 h) on aerobic performance and thermoregulatory responses in rats exercised on a treadmill at different environmental conditions. Adult male Wistar rats were subjected to rapid eye movement sleep deprivation (RSD) using the modified multiple platform method and were then subjected to an incremental-speed exercise until they were fatigued. Treadmill running was performed in a temperate (24°C) or warm (31°C) environment, and the colonic temperature (an index of core body temperature; TCORE) and the tail-skin temperature (TSKIN; an index of cutaneous heat loss) were recorded. 24-h and 96-h RSD produced small magnitude reductions in aerobic performance (Cohen's d = 0.47-0.58) and minor changes in thermoregulation. Relative to control rats, sleep-deprived rats showed a higher TCORE at the exercise initiation and a higher threshold for activating cutaneous heat loss, but unchanged TCORE and TSKIN at fatigue. Exercise at 31°C induced large reductions in performance (d = 0.82-1.29) and marked changes in thermoregulation, as evidenced by higher TCORE and TSKIN at fatigue, compared to exercise at 24°C. Interestingly, none of the effects induced by RSD were exacerbated by environmental heat stress and vice-versa, indicating that both conditions did not interact. We conclude that RSD and heat stress modulate aerobic performance and thermoregulatory responses by acting independently.

RESUMO

Evidence has shown that brain and abdominal (T abd) temperatures are regulated by distinct physiological mechanisms. Thus, the present study examined whether central cholinergic stimulation would change the dynamics of exercise-induced increases in T abd and thalamic temperature (T thal), an index of brain temperature. Adult male Wistar rats were used in all of the experiments. Two guide cannulae were implanted in the rats, one in the thalamus and the other in the right lateral cerebral ventricle, to measure T thal and to centrally inject a cholinergic agonist, respectively. Then, a temperature sensor was implanted in the abdominal cavity. On the day of the experiments, the rats received an intracerebroventricular injection of 2 µL of 10(-2)M physostigmine (Phy) or a vehicle solution (Veh) and were subjected to treadmill running until volitional fatigue occurred. T thal was measured using a thermistor connected to a multimeter, and T abd was recorded by telemetry. Phy injection delayed the exercise-induced increases in T thal (37.6 ± 0.2°C Phy vs 38.7 ± 0.1°C Veh at the 10th min of exercise) and in T abd. Despite the delayed hyperthermia, Phy did not change the rats' physical performance. In addition, the more rapid exercise-induced increase in T thal relative to Tabd in the rats treated with Veh was abolished by Phy. Collectively, our data indicate that central cholinergic stimulation affects the dynamics of exercise-induced increases in T thal and T abd. These results also provide evidence of the involvement of cholinoceptors in the modulation of brain heat loss during physical exercise.

Assuntos

RESUMO

Rats are used worldwide in experiments that aim to investigate the physiological responses induced by a physical exercise session. Changes in body temperature regulation, which may affect both the performance and the health of exercising rats, are evident among these physiological responses. Despite the universal use of rats in biomedical research involving exercise, investigators often overlook important methodological issues that hamper the accurate measurement of clear thermoregulatory responses. Moreover, much debate exists regarding whether the outcome of rat experiments can be extrapolated to human physiology, including thermal physiology. Herein, we described the impact of different exercise intensities, durations and protocols and environmental conditions on running-induced thermoregulatory changes. We focused on treadmill running because this type of exercise allows for precise control of the exercise intensity and the measurement of autonomic thermoeffectors associated with heat production and loss. Some methodological issues regarding rat experiments, such as the sites for body temperature measurements and the time of day at which experiments are performed, were also discussed. In addition, we analyzed the influence of a high body surface area-to-mass ratio and limited evaporative cooling on the exercise-induced thermoregulatory responses of running rats and then compared these responses in rats to those observed in humans. Collectively, the data presented in this review represent a reference source for investigators interested in studying exercise thermoregulation in rats. In addition, the present data indicate that the thermoregulatory responses of exercising rats can be extrapolated, with some important limitations, to human thermal physiology.

RESUMO

O objetivo deste estudo foi verificar o efeito da suplementação de creatina sobre o desempenho nos testes de Wingate de 10 e 30 segundos além da sua influência na concentração de lactato, ureia, creatinina e massa corporal de indivíduos fisicamente ativos. Para realização da pesquisa foram selecionados nove voluntários, sendo divididos dentro de dois grupos utilizando o procedimento duplo-cego: grupo creatina (n = 4) e grupo placebo (n = 5). A suplementação foi realizada via oral durante 10 dias, sendo que o grupo creatina ingeriu 20g de creatina (4x ao dia) nos primeiros cinco dias, seguida de uma ingesta de 5g/dia até o 10º dia. O grupo placebo recebeu a mesma dosagem, porém de maltodextrina como placebo. O protocolo de teste realizado antes e após o período de suplementação constou de um teste de Wingate adaptado de 10 segundos, seguido de um intervalo de 20 minutos para aplicação de um teste de Wingate de 30 segundos. Foram coletadas amostras de sangue antes e após o período de suplementação para análise de creatinina e ureia, lactato em repouso, 90 segundos após o teste de 10 segundos e 180 segundos após o teste de 30 segundos. A suplementação de creatina promoveu um aumento significativo (p < 0,05) na potência máxima durante o teste de 30 segundos, na potência média no teste de 10 segundos, além da concentração de creatinina. Os resultados sugerem que a suplementação de creatina pode melhorar o desempenho dos indivíduos durante exercício de alta intensidade e curta duração realizado no cicloergômetro, mas produz aumento da concentração de creatinina em repouso.

The aim of this research was to verify the effect of the creatine supplementation on performance in the 10 and 30-second Wingate tests, besides its influence in the creatinine, urea and lactate concentration and body mass of physically active men. This research selected nine volunteers, who were then separated in two groups using the double-blind procedure: creatine group (n=4) and placebo group (n=5).The supplementation was orally administered during ten days. The creatine group ingested 20g of creatine (4 times a day) in the first five days, followed by an ingestion of 5 g/day until the tenth day. The placebo group received the same dosage, but of maltodextrine instead, as placebo. The test protocol performed before and after the supplementation period consisted of an adapted 10-second Wingate test, followed by an interval of 20 minutes for application of the 30-second Wingate test .Blood samples were collected before and after the supplementation period for analysis of creatinine and urea, lactate at rest, 90 seconds after the 10-second test and 180 seconds after the 30-second test. Creatine supplementation promoted significant raise (p<0.05) in maximal power output during the 30-second test, in the mean power output in the 10 second-test, besides the creatinine concentration. The results suggest that creatine supplementation can improve individual performance in high intensity activities and short duration made in cycle ergometer; however, creatine supplementation increases the creatinine concentration at rest.