Effects of caffeine and glucose ingestion on metabolic and respiratory functions during prolonged exercise

The effects of caffeine and the effects of glucose on athletic performance have been well documented. The purpose of this investigation was to examine the effects of caffeine, used separately or in combination with glucose, on blood glucose, blood lactate, plasma FFA, respiratory exchange ratio (R), VO2 and perceived exertion (RPE) during an extended submaximal treadmill run (n = 6). The four treatments administered were: (a) placebo ingested both prior to and during exercise (P + P); (b) caffeine ingested 60 min pre-exercise and a placebo 30 min prior to and during exercise (C + P); (c) placebo ingested 60 min pre-exercise and 10% glucose ingested 30 min prior to and during exercise (P + G); and (d) caffeine ingested 60 min pre-exercise and 10% glucose ingested 30 min prior to and during exercise (C + G). Results showed that the P + G and C + G treatments produced significantly higher mean blood glucose levels than P + P (P 0.01) and significantly higher blood lactate levels than P + P and C + P (P0.05). Plasma FFA levels were found to be significantly higher and R values significantly lower for C + P than for the other three treatments (P0.01). Furthermore, subjects were found to perceive exercise as significantly easier with treatment C + P and significantly more difficult with treatment C + G when compared to P + P (P 0.01). The C + P treatment exhibited the most beneficial effects overall when performing extended submaximal exercise compared to the other three treatments.