The Effects of Caffeine and Quercetin on Isometric Knee Extension Exercise at 110% Critical Torque.

Adenosine receptor antagonism appears to be the accepted mechanism behind caffeine’s ergogenic effects on prolonged exercise. The flavonoid quercetin has also been demonstrated to antagonise adenosine receptors, yet quercetin’s effects on exercise performance are unknown. The current study sought to compare the effects of acute caffeine and quercetin administration on exercise capacity and fatigue progression in intermittent isometric knee extension exercise. Eight team-sport and endurance male athletes (23.51 ± 1.94 years; 1.83 ± 5.21 m; 79.33 ± 7.66 kg) completed an intermittent isometric knee extension exercise protocol with regular MVCs to exhaustion at 110% critical torque with either caffeine (6 mg·kg-1), quercetin (25 mg·kg-1) or placebo in a double blind, randomised crossover design. Statistical analysis demonstrated no significant difference in time to exhaustion (failure to maintain 95% of target torque) between caffeine (921.8 ± 415.4 s) quercetin (836.3 ± 312.4 s) and placebo (776.3 ± 566.0 s) (p > 0.05, partial ŋ2 = 0.249). No difference was found for the change in torque or EMG amplitude during MVCs performed each minute throughout the protocol, and no difference was found for EMG amplitude or median frequency during contractions at 110% critical torque (p > 0.05). Caffeine and quercetin appear to have no ergogenic effect on intermittent isometric knee extension exercise at 110% critical torque.