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

Abstract

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∙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∙min^{- 1}), mean arterial blood pressure (98 ± 8 vs 92 ± 10 mmHg), plasma glucose (5.6 ± 0.7 vs 5.3 ± 0.6 mmol∙l^{- 1}) and lactate (3.3 ± 1.2 vs 2.9 ± 1.2 mmol∙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.

Keywords: Biochemical responses; Endurance performance; Ergogenic aid; Explosiveness.

Fig. 1

Means and SD of time to exhaustion with caffeine (solid bars) and placebo (hatched bars). Participants were divided according to cardiorespiratory (left) or neuromuscular fitness (right), with high groups shown in black and medium groups shown in grey. There was a significant treatment effect (p < 0.001)

Fig. 2

Means and SD of countermovement jump height with caffeine (solid bars) and placebo (hatched bars). Participants were divided according to cardiorespiratory (a) or neuromuscular fitness (b), with high groups shown in black and medium groups shown in grey. One to 5 correspond to time points as follows: 1, before the start of the trial; 2, between the 1st and 2nd periods; 3, immediately after the end of the 2nd period; 4, immediately before the start of the 3rd period; 5: between the 3rd and 4th periods. There were significant treatment and time effects in both a and b, as well as a significant group effect (by design) in b (p < 0.05)

Fig. 3

Means and SD of plasma glucose (a), lactate (b), glycerol (c), NEFA (d) and epinephrine (e) with caffeine (full circles) and placebo (open circles). Participants were divided according to cardiorespiratory (left) or neuromuscular fitness (right), with high groups shown with solid lines and medium groups shown with dashed lines. One to 7 correspond to time points as follows: 1, 75 min before the start of the trial; 2, 15 min before the start of the trial; 3, between the 1st and 2nd periods; 4, immediately after the end of the 2nd period; 5, immediately before the start of the 3rd period; 6: between the 3rd and 4th periods; 7, at exhaustion. *Significant treatment effect (p ≤ 0.01). †Significant time effect (p < 0.001)