Effects of caffeine ingestion on metabolism and performance during graded exercise.
Seven trained men were studied during graded cycle ergometer exercise to assess the effects of caffeine ingestion on metabolism and performance. A single blind experimental procedure was followed with one trial being performed 60 min after the subject ingested caffeine (5 mg . kg-1) while the second trial required the subject to ingest a placebo with the treatment order being counterbalanced. Subjects began exercising at a work load of 30 W while the load was increased by an additional 30 W every 3 min until the subject could not maintain the desired pedal frequency. Venous blood samples were obtained at each work load and assayed for free fatty acids (FFA), glycerol, lactic acid, and caffeine. There was no significant difference (p greater than 0.05) in time to exhaustion between the two experimental treatments. Resting measurements of FFA and glycerol showed that ingestion of caffeine brought about significant (p less than 0.05) increases in plasma levels of both FFA and glycerol compared to values obtained during the placebo treatment. The rate of blood lactic acid accumulation was not significantly different (p greater than 0.05) between the two exercise tests. These data suggest that a small dose of caffeine does not change the rate of blood lactate accumulation nor does it enhance performance during graded cycle ergometer exercise.