Laboratory-based studies have clearly established that caffeine supplementation has ergogenic effects(Reference Ganio, Klau and Casa1), but it is unclear to what extent these effects translate to the field setting(Reference Burke2). We conducted a series of cross-over studies to establish the effect of caffeine gum on the performance of recreationally trained runners taking part in parkruns. Parkruns are free to enter, timed, 5 km running events held in numerous parks around the UK every Saturday morning(3).
A total of 36 recreationally trained runners (M = 31, F = 5) capable of running 5 km in < 25 min were recruited to 3 studies taking place at Sheffield Hallam parkrun. For each study, 6 runners were allocated into a randomised, placebo-controlled, cross-over intervention with caffeine gum as the active treatment (300 mg; Military energy gum, Marketright Inc., USA) and 6 were allocated into a non-intervention group. The purpose of the non-intervention group was to adjust for the effect of variable weather conditions on performance. Runners in the randomised cross-over interventions chewed caffeine gum or placebo gum for 5 min, starting 30 minute before each 5 km parkrun. Finishing time and ratings of perceived exertion (RPE) were recorded. A primary statistical analysis used the data from the cross-over interventions alone. The effect of caffeinated gum on performance and RPE were analysed using paired samples t-tests. A secondary statistical analysis used the non-intervention group data in an attempt to adjust for effect of changing weather conditions on performance times. The times of each runner in the 3 cross-over interventions were divided by the mean time of the associated group of non-intervention runners to produce a ratio. The ratio data was then analysed using a paired samples t-test. The study was approved by the Ethics Committee of Sheffield Business School, Sheffield Hallam University and the Research Review Board of parkrun.
Of the 36 runners recruited to the 3 studies, 29 completed both runs (14 intervention runners and 15 non-intervention runners). The primary statistical analysis revealed that caffeine gum improved 5 km parkrun performance by a mean of 17·28 s (95 % CI 4·19, 30·37; P = 0·014) and decreased RPE by 1·21 (95 % CI 0·30, 2·13; P = 0·013). Adjusting the finishing time data using the mean times of the non-intervention groups attenuated the statistical significance (P = 0·037).
In conclusion, caffeine gum evokes a modest improvement in 5 km running performance in recreational runners taking part in parkrun events. Moreover, the improved performance is accompanied by a reduction in RPE.
