The effect of different dosages of caffeine on time to exhaustion in prolonged exercise in trained athletes (a meta analysis)

Abstract

Background The world anti doping organisation removed caffeine from the banned list of substances in 2004; yet, research shows over recent years caffeine has become one of the most widely used ergogenic aids by athletes in the UK. This analysis investigates one of the suggested ergogenic benefits of caffeine, increasing time to exhaustion, and whether this effect relates to specific dosages of caffeine ingested before exercise.

Objectives To assess the effects of two different dosages of caffeine on trained athlete’s time to exhaustion in endurance exercise.

Search methods “caffeine” and “time to exhaustion” were entered into Pubmed, Scirus and Google Scholar. “Humans, randomised, double blind trial” were entered as limiters. The search was completed using the Athens log in through the University of Plymouth on 29 January 2010.

Selection criteria Randomised, double blind trials which reported the effects of ingesting dosages of caffeine of either 3-6 mg per kg of body weight (mg/kg) or 9-13mg/kg and a placebo for time to exhaustion in prolonged exercise were used in this meta analysis.

Data collection and analysis The data was extracted by the author using strict inclusion criteria. The mean difference with 95% confidence intervals, fixed effects was analysed using RevMan 5 for time to exhaustion when ingesting either caffeine or the placebo one hour before exercise.

Main results Thirty studies were available via the University of Plymouth subscription. Six were eligible as having the correct inclusion criteria and measuring the correct endpoints. Overall, caffeine increased time to exhaustion in comparison to the placebo with a mean increase of 11.94 minutes The dose range 3-6mg/kg had a significant effect on time to exhaustion in comparison to the placebo with a mean increase of 11.99 minutes. The dose range 9-13mg/kg also had a significant effect on time to exhaustion when compared to the placebo with a mean increase of 11.81 minutes. There was no significant difference between the mean differences for the two dose ranges and so the smaller dose (3-6 mg/kg) of caffeine produced a similar effect on time to exhaustion as the larger dose (9-13mg/kg).

Conclusions Caffeine significantly increased time to exhaustion in comparison to the placebo across all studies. There was no dose- response relationship evident for the effects of caffeine on time to exhaustion. Due to the side effects noted for caffeine doses residing in the higher range (9-13mg/kg), it may be more beneficial for athletes to ingest doses in the lower range (3-6mg/kg), as the adverse effects may surpass the ergogenic benefits.