Effects of caffeine on the rate of perceived exertion

The role of caffeine in improving performance in endurance exercises is controversial and its mechanism of action is not well understood. The purpose of the present study was to evaluate the effects of caffeine on the rate of perceived exertion (RPE) by exercising athletes. Six male non-smoking runners, aged 26.8 ñ 4.9 years (mean ñ SD), who had been in training continuously for at least two years before the experiment were studied. Mean maximum oxygen consumption (VO2max) was 61.21 ñ 5.36 ml kg**-1 min**-1. The subjects were asked to exercise on a bicycle ergometer for 3 min each at 300 and 600 kg m min**-1, after which the work load was elevated to 1200 kg m min**-1 and they exercised until exhaustion. In order to evaluate the effects of caffeine, the exercicse was performed twice following the ingestion of 200 ml decaffeinated coffee with and without caffeine (5 mg/kg body veight). Caffeine had no significant effect on exercise time, pulmonary ventilation, oxygen consumption, carbon dioxide extraction or exchange respiratory ratio, but the RPE was significantly lower (P<0.05) at the work load of 1200 kg m min**-1 after the ingestion of caffeine for both trials I and II. The present results suggest that metabolic acidosis and glycogen depletion were not the main causes of exhaustion

Breathing pattern during pharmacological activation and blockade of the intermediate area of the ventrolateral surface of the cat medulla

The present study analyzes the respiratory pattern of chloralose- (50-60 mg/kg,iv) anesthetized cats treated with Nembutal (NE) (30 mg/ml), glycine (GL) (200 mg/ml) or leptazol (LE) (200 mg/ml) topically applied to the intermediate area of the ventrolateral surface of the medulla oblongata in a volume of 20 micronl. Application of NE and GL produced a decrease in ventilation (-24%) and tidal volume (-25%) suggesting that the intermediate area facilitates respiratory drive and inhibits the inspiratory off-switch mechanism. These results are consistent with the view that intermediate area is necessary for the central chemosensitivity to CO2. The topical application of LE produced an increase in inspiration time (12.5%), expiration time (20.8%) and tidal volume (7%). The increased tidal volume caused by LE is compatible with it action as a GL antagonist