Effect of repeated caffeine ingestion on repeated exhaustive exercise endurance

Purpose: The purpose of this study was to examine the effect of repeated doses of caffeine on repeated exercise endurance. Methods: Nine male caffeine users performed exercise rides (ER) to exhaustion at 80% VO2max after ingesting a placebo, 5 mg(.)kg(-1) of caffeine, or 2.5 mk(.)kg(-1) of caffeine 1 h before the ER. Two ER were performed weekly on the same day once in the morning (AM) and 5 h later in the afternoon (PM). There were four treatments containing either caffeine or placebo, i.e., trial A representing 5-mg(.)kg(-1) caffeine in the AM and 2.5-mg(.)kg(-1) caffeine in the PM; trial B, which was placebo in both AM and PM; trial C representing 5-mg(.)kg(-1) caffeine in the AM and placebo in the PM; and trial D representing a placebo in the AM and 5-mg(.)kg(-1) caffeine in the PM. The order of the treatment trials was double blind and randomized. Results: Caffeine ingestion significantly increased exercise time to exhaustion in the AM (trial A 24.9 +/- 10.2 min and trial C 21.8 +/- 4.9 vs trial B 18.0 +/- 6.4 min and D 17.7 +/- 4:3 min). This effect was maintained in the PM and greater than placebo (B 18.3 +/- 4.8 min) regardless of whether redosing (trial A 21.5 +/- 8.6 min) or placebo (trial C 21.0 +/- 6.8) followed the initial morning dose. Caffeine dosing in the PM (trial D 22.4 +/- 7.2 min) also increased ER after placebo trial D in the AM. Conclusions: It was concluded that redosing with caffeine after exhaustive exercise in the AM was not necessary to maintain the ergogenic effect of the drug during subsequent exercise 6 h later.