Acute caffeine intake increases muscle oxygen saturation during a maximal incremental exercise test

Aims The main mechanism behind caffeine's ergogenicity lies in its tendency to bind to adenosine receptors, although other mechanisms might be involved. The aim of this investigation was to analyse the effects of caffeine on muscle oxygen saturation during exercise of increasing intensity. Methods Thirteen healthy and active individuals volunteered to participate in a randomized, double blind, placebo-controlled crossover trial. During 2 different trials, participants either ingested a placebo (cellulose) or 3 mg/kg of caffeine. After waiting for 60 min to absorb the substances, participants underwent a maximal ramp cycle ergometer test (25 W/min). Near infrared spectrometers were positioned on each leg's vastus lateralis to monitor tissue O-2 saturation. Blood lactate concentration was measured 1 min after the end of the exercise test. Results In comparison to the placebo, the ingestion of caffeine improved the maximal wattage (258 +/- 50 vs 271 +/- 54 W, respectively, P < .001, effect size [ES] = 0.27; 95% confidence interval [CI] 0.14-0.35) and blood lactate concentration (11.9 +/- 3.8 vs 13.7 +/- 3.5 mmol/L, P = .029, ES = 0.38; 95% CI 0.14-0.75) at the end of the test. Caffeine increased muscle oxygen saturation at several exercise workloads with a main effect found in respect to the placebo (F = 6.28, P = .029; ES = 0.30 to 0.54; 95% CI 0.01-0.78). Peak pulmonary ventilation (124 +/- 29 vs 129 +/- 23 L/min, P = 0.035, ES = 0.25; 95% CI 0.07-0.40) and peak oxygen uptake (3.18 +/- 0.70 vs 3.33 +/- 0.88 L/min, P = 0.032, ES = 0.26; 95% CI 0.08-0.51) were also increased with caffeine. Conclusion Acute ingestion of 3 mg/kg of caffeine improved peak aerobic performance and increased peak pulmonary ventilation. In addition, caffeine induced changes in muscle oxygen saturation during submaximal workloads, suggesting that this mechanism might also contribute to caffeine's ergogenic effect.