The metabolic and performance effects of caffeine compared to coffee during endurance exercise

Abstract

There is consistent evidence supporting the ergogenic effects of caffeine for endurance based exercise. However, whether caffeine ingested through coffee has the same effects is still subject to debate. The primary aim of the study was to investigate the performance enhancing effects of caffeine and coffee using a time trial performance test, while also investigating the metabolic effects of caffeine and coffee. In a single-blind, crossover, randomised counter-balanced study design, eight trained male cyclists/triathletes (Mean ± SD: Age 41 ± 7 y, Height 1.80 ± 0.04 m, Weight 78.9 ± 4.1 kg, VO2 max 58 ± 3 ml • kg(-1) • min(-1)) completed 30 min of steady-state (SS) cycling at approximately 55% VO2max followed by a 45 min energy based target time trial (TT). One hour prior to exercise each athlete consumed drinks consisting of caffeine (5 mg CAF/kg BW), instant coffee (5 mg CAF/kg BW), instant decaffeinated coffee or placebo. The set workloads produced similar relative exercise intensities during the SS for all drinks, with no observed difference in carbohydrate or fat oxidation. Performance times during the TT were significantly faster (~5.0%) for both caffeine and coffee when compared to placebo and decaf (38.35 ± 1.53, 38.27 ± 1.80, 40.23 ± 1.98, 40.31 ± 1.22 min respectively, p<0.05). The significantly faster performance times were similar for both caffeine and coffee. Average power for caffeine and coffee during the TT was significantly greater when compared to placebo and decaf (294 ± 21 W, 291 ± 22 W, 277 ± 14 W, 276 ± 23 W respectively, p<0.05). No significant differences were observed between placebo and decaf during the TT. The present study illustrates that both caffeine (5 mg/kg/BW) and coffee (5 mg/kg/BW) consumed 1 h prior to exercise can improve endurance exercise performance.

Figure 1. Carbohydrate oxidation (g/min) (A) and fat oxidation (g/min) (B) rates during 30 min steady state exercise (55% VO₂ max) 1 hour following ingestion of caffeine, coffee, decaf or placebo beverages.

Data represented seen as Closed circles – Caffeine Open circles – Caffeinated Coffee Closed triangles – Decaffeinated coffee Open triangles – Placebo. Means ± SE n = 8

Figure 2. Plasma metabolite responses at rest (t = -60-0) and during 30 min steady state exercise (55% VO₂ max) (t = 0–30) following ingestion of caffeine, coffee, decaf or placebo beverages.

A Glucose. B Fatty acids (FA). C Glycerol. D Lactate. Data represented seen as Closed circles – Caffeine Open circles – Caffeinated Coffee Closed triangles – Decaffeinated coffee Open triangles – Placebo. a Sig. different between CAF and DECAF (p<0.05) b Sig. different between CAF and PLA (p<0.05) c Sig. different between COF and DECAF (p<0.05) d Sig. different between COF and PLA (p<0.05). Means ± SE n = 7.

Figure 3. Plasma caffeine concentrations following ingestion of caffeine, coffee, decaf or placebo beverages.

a CAF significantly different to DECAF and PLA (p<0.001) b COF significantly different to DECAF and PLA (p<0.05). Data represented seen as Closed circles – Caffeine Open circles – Caffeinated Coffee Closed triangles – Decaffeinated coffee Open triangles – Placebo Means ± SE n = 7.

Figure 4. Time trial finishing time (min) for caffeine, coffee, decaf or placebo beverages a CAF significantly different to DECAF and PLA (p<0.05) b COF significantly different to DECAF and PLA (p<0.05).

Data represented seen as Closed bar– Caffeine Open bar – Caffeinated Coffee Dark grey bar– Decaffeinated coffee Light grey bar– Placebo. Means ± SE n = 8.