EFFECT OF CAFFEINE INGESTION ON PERCEPTION OF EFFORT AND SUBSEQUENT WORK PRODUCTION

The purpose of this investigation was to determine the effect of caffe ine ingestion on work output at various levels of perceived exertion d uring 30 min of isokinetic variable-resistance cycling exercise. Ten s ubjects completed six trials 1 hr after consuming either 6 mg . kg(-1) caffeine (3 trials) or a placebo (3 trials). During each trial the su bjects cycled at what they perceived to be a rating of 9 on the Borg r ating of perceived exertion scale for the first 10 min, a rating of 12 for the next 10 min, and a rating of 15 for the final 10 min. Total w ork performed during the caffeine trials averaged 277.8 +/-26.1 kJ, wh ereas the mean total work during the placebo trials was 246.7 +/- 21.5 kJ (p<.05). Blood glycerol and free fatty acid levels increased over time to a significantly greater degree in the caffeine trials than in the placebo trials (p<.05). However, there were no significant differe nces between conditions in respiratory exchange ratio. These data sugg est that caffeine may play an ergogenic role in exercise performance b y altering both neural perception of effort and substrate availability .