THE EFFECT OF CAFFEINE ON ENDURANCE PERFORMANCE AFTER NON-SELECTIVE BETA-BLOCKER ADMINISTRATION 916

Abstract

Caffeine ingestion has been shown to increase aerobic endurance exercise performance. Beta-blocker administration, on the other hand, reduces endurance performance. It has been suggested that caffeine acts by increasing lipolysis, thus sparing glycogen. Beta-blockers inhibit lipolysis. In this study we investigated whether caffeine is able to restore the impaired endurance performance after beta-blocker administration. Fifteen endurance-trained male athletes performed three trials (cycling at 70% Wmax until exhaustion). 90 min before the trial, subjects ingested a capsule containing either 80 mg propranolol (Pr), or 80 mg propranolol plus 5 mg/kg caffeine (Pr+C), or placebo (Pl). The trials were performed double-bindly and the order was randomized. Heart rate at 10 min exercise was 163±9 bpm after Pl and was reduced to 129±15 bpm after Pr and to 131±10 bpm after Pr+C(p<0.001), indicating effective and equivalent beta-blockade after Pr and Pr+C. Endurance time was 79±20 min after Pl, and was reduced to 23±11 min after Pr and to 31±17 min after Pr+C (p<0.05). The difference in endurance time between Pr and Pr+C was not statistically significant, although in 11 out of 15 subjects endurance time was higher after Pr+C than after Pr. Plasma non-esterified fatty acid (NEFA) concentrations were lower after Pr and Pr+C than after Pl (during recovery: 1.16±0.53 mmol/l after Pl, 0.19±0.10 mmol/l after Pr, 0.26±0.14 mmol/l after Pr+C, p<0.05), but there were no differences in plasma NEFA after Pr and Pr+C. The results demonstrate that caffeine ingestion does not fully restore the impaired endurance performance after beta-blocker administration. Although, we cannot fully rule out the possibility that caffeine has some positive effect on endurance time after beta-blockade, it is unlikely that such an effect is mediated by a substantial effect on lipolysis, as reflected by plasma NEFA concentrations.