Effect of caffeine on muscle oxygen saturation during short-term all-out exercise: a double-blind randomized crossover study

Purpose The ergogenic effect of oral caffeine administration on short-term all-out exercise performance is well established. However, the potential mechanisms associated with caffeine's ergogenicity in this type of exercise are poorly understood. The aim of this study was to investigate whether caffeine intake modifies muscle oxygen saturation during the 15-s Wingate Anaerobic Test. Methods Fifteen moderately trained individuals (body mass = 67.4 +/- 12.3 kg; height 171.3 +/- 6.9 cm; age 31 +/- 6 years) took part in two identical experimental trials after the ingestion of (a) 3 mg/kg of caffeine or (b) 3 mg/kg of cellulose (placebo). After 60 min for substances absorption, participants performed a 15-s Wingate test on a cycle ergometer against a load representing 7.5% of participant's body mass. Muscle oxygen saturation was continuously measured during exercise with near-infrared spectroscopy and blood lactate concentration was measured 1 min after exercise. Results In comparison to the placebo, the oral administration of caffeine increased peak power by 2.9 +/- 4.5% (from 9.65 +/- 1.38 to. 9.92 +/- 1.40 W/kg, P = 0.038; effect size (ES), 95% confidence intervals = 0.28, 0.05-0.51), mean power by 3.5 +/- 6.2% (from 8.30 +/- 1.08 to 8.57 +/- 1.12 W/kg, P = 0.044; ES = 0.36, 0.01-0.71) and blood lactate concentration by 20.9 +/- 24.7% (from 12.4 +/- 2.6 to 14.8 +/- 4.0 mmol/L, P = 0.005; ES = 0.59, 0.16-1.02). However, caffeine did not modify the curve of muscle oxygen desaturation during exercise (lowest value was 23.1 +/- 14.1 and 23.4 +/- 14.1%, P = 0.940). Conclusion Caffeine's ergogenic effect during short-term all-out exercise seems to be associated with an increased glycolytic metabolism with no influence of enhanced muscle oxygen saturation.