SummaryCaffeine is one of the famous ergogenic aids in the athletic field. Caffeine has been known to stimulate lipolysis that spares stored glycogen utilization during moderate intensity exercise. Therefore, we investigated the effects of caffeine ingestion on exercise per formance in rats and athletes. Rats were administered the caffeine (6mg/kg) 1h prior to the exercise then were run on a treadmill at a speed of 20m/min. They were decapitated at 0min, 30min, 60min of exercise, and exhausted time point. Human subjects ingested the caffeine (5mg/kg) 1h prior to the exercise. They exercised on a cycle ergometer at 60% of their VO2max for 45min, and then the exercise intensity was increased to 80% of their VO 2max until exhaustion. Blood and breathing gas samples were collected and calculated every 10min during exercise. Respiratory exchange ratio of the caffeine trial was signifi cantly lower than that of the placebo trial in the athletes' study (p<0.05). Blood free fatty acid (FFA) levels in studies of both rats and athletes were increased by caffeine ingestion during exercise (p<0.05). Blood lactate levels were also increased during exercise in both rats and athletes (p<0.05). Increased FFA and glycerol concentrations reduced glycogen utilization during exercise compared with placebo group in rats. In addition, endurance time to exhaustion was significantly increased by the caffeine ingestion in both rats and ath letes (p<0.05). These results suggest that the caffeine ingestion enhanced endurance per formance resulting from spare stored glycogen with increasing lipolysis from adipose tissues and fat oxidation during exercise both in rats and in athletes.
SummaryThe effects of body weight cycling on energy metabolism and body fat accumulation were examined in sedentary and exercised rats. Ten rats were sacrificed before the experiment to obtain basal data, and then 90 rats were divided into three groups; control (CN), food restricted (FR) and weight cycling (WC). Food intake in rats of the FR group was restricted constantly to 70% of the intake of the CN group. The rats of WC group were subjected to four bouts of weight cycling consisting of 7 -days food restriction followed by 7-days refeeding, but were fed the same total amount of dietary energy as that of the FR group throughout the experimental period. The rats of all groups were meal-fed twice a day.Half of the rats in each group were exercised by running on a treadmill (30min/day) throughout the experimental period. The body weight, abdominal adipose tissue weight, body fat, body protein and energy restoration for the study in both sedentary and exercised groups were greater in the WC group than in the FR group. The resting metabolic rate of the WC group after four bouts of weight cycling was lower than that of the FR group in the sedentary rats, but this difference was not observed in the exercised rats. Also, the thermic effect of food (TEF) in the sedentary rats for 6h after a meal was significantly less in the WC group as compared to that of the FR group. However, the TEF for the exercised rats was not different between the two groups. The serum insulin level,
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