BELL, D. G., and T. M. MCLELLAN. Effect of Repeated Caffeine Ingestion on Repeated Exhaustive Exercise Endurance. Med. Sci. Sports Exerc., Vol. 35, No. 8, pp. 1348–1354, 2003.
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% V̇O2max after ingesting a placebo, 5 mg·kg−1 of caffeine, or 2.5 mg·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.
The ergogenic effects of caffeine ingestion during submaximal exercise are well documented in a number of recent reviews (7,12,22). Most studies have looked at exercise endurance approximately 1 h after caffeine ingestion when plasma concentrations of the drug are close to maximal (4,13,14,23–25,27). Recently, we reported that both the magnitude and duration of the ergogenic effect that followed a 5-mg·kg−1 dose of caffeine differed between users and nonusers of the drug (1). For caffeine users, exercise endurance was improved approximately 20% one and three hours after caffeine ingestion, but performance had returned to placebo levels 6 h later. In contrast, endurance was increased by 30% for nonusers of the drug for up to 6 h after caffeine ingestion. In that study, plasma caffeine concentrations decreased from 36 μmol·L−1 1 h after caffeine ingestion to 27 μmol·L−1 6 h later for users of the drug (1), implying that this lower concentration was insufficient to induce the ergogenic effect. Thus, the focus of the present study was to examine whether restoring plasma concentrations to these higher values would again be associated with an improvement in exercise endurance. For athletes and the military, it would seem critical to know not only when a particular ergogenic aid should be taken to produce its effect but also when and whether further dosing should be used to maintain the ergogenic benefit. It is not uncommon for athletic events or military operations to involve repeated bouts of exercise or work throughout the day. Any strategy that can be adopted to enhance the performance of the athlete or soldier over these periods would be advantageous.
To our knowledge, the evaluation of exercise endurance during the morning and afternoon after redosing of caffeine has not been studied. Others have examined the effects of repeated dosing of caffeine throughout a prolonged exercise task on the performance of a subsequent time trial or exercise test to exhaustion (5,8). For example, Cox et al. (5) reported a small 3% improvement in time trial performance that followed 2 h of exercise at 70% V̇O2max for trained cyclists regardless of whether 6 mg·kg−1 of caffeine was ingested in a single dose before or divided into six equal doses and administered at 20-min intervals throughout the 2 h of exercise. In contrast, Falk et al. (8) observed that cycle time to exhaustion at 90% V̇O2max was not improved after an 8-h, 40-km march when blood caffeine levels were maintained at high levels with an initial 5-mg·kg−1 dose of the drug that was supplemented after 3 and 5 h of marching with additional 2.5-mg·kg−1 caffeine doses. However, neither of these studies examined repeated exercise tests that were separated by a period of recovery.
It was the purpose of this study, therefore, to determine whether redosing with caffeine would be an efficacious strategy to maintain the ergogenic effects of the drug during repeated exercise bouts i.e., one in the morning and another in the afternoon. Thus, one exhaustive exercise bout at 80% V̇O2max was performed 1 h after an initial 5-mg·kg−1 dose of caffeine was ingested in the morning, and the second was performed 1 h after an additional 2.5-mg·kg−1 maintenance dose was administered in the afternoon. The 2.5-mg·kg−1 dose was administered 5 h after the initial dose was consumed. We hypothesized that this dosing regimen would maintain the ergogenic effect of the drug during exercise performed in the afternoon at a similar level to the effect observed during the morning exercise.
Operational Medicine Section, Defence R&D Canada–Toronto, Ontario, CANADA
Address for correspondence: D. G. Bell, Defence R&D Canada–Toronto, 1133 Sheppard Avenue West, P. O. Box 2000, Toronto, Ontario, Canada, M3M 3B9; E-mail: email@example.com.
Submitted for publication December 2002.
Accepted for publication April 2003.