Caffeine supplementation is ergogenic in soccer players independent of cardiorespiratory or neuromuscular fitness levels

Background Equivocal findings examining the influence of caffeine on performance and biological responses to exercise may be due to inter-individual variability in cardiorespiratory or neuromuscular fitness. This study examined whether the effects of caffeine ingestion on exercise performance and biological responses to prolonged intermittent exercise to exhaustion depend on cardiorespiratory or neuromuscular fitness. Methods Twenty male soccer players, separated according to either cardiorespiratory fitness (high vs medium) or neuromuscular fitness (high vs medium) underwent two trials simulating the cardiovascular demands of a soccer game to exhaustion on treadmill after ingesting either caffeine (6 mg center dot kg(- 1)) or placebo. Physical performance, cardiorespiratory and metabolic parameters and blood metabolites were evaluated. Results Time to exhaustion (719 +/- 288 vs 469 +/- 228 s), jump height (42.7 +/- 4.2 vs 38.6 +/- 4.4 cm), heart rate (163 +/- 12 vs 157 +/- 13 b center dot min(- 1)), mean arterial blood pressure (98 +/- 8 vs 92 +/- 10 mmHg), plasma glucose (5.6 +/- 0.7 vs 5.3 +/- 0.6 mmol center dot l(- 1)) and lactate (3.3 +/- 1.2 vs 2.9 +/- 1.2 mmol center dot l(- 1)) were higher, while rating of perceived exertion (12.6 +/- 1.7 vs 13.3 +/- 1.6) was lower with caffeine vs placebo (p < 0.01), independent of cardiorespiratory or neuromuscular fitness level. Reaction time; plasma glycerol, non-esterified fatty acids and epinephrine; carbohydrate and fat oxidation rates; and energy expenditure were not affected by caffeine (p > 0.05). Conclusions Caffeine was effective in improving endurance and neuromuscular performance in athletes with either high or medium cardiorespiratory and neuromuscular fitness. Cardiorespiratory and neuromuscular fitness do not appear to modulate the ergogenic effects of caffeine supplementation in well-trained athletes.