Effect of a Commercially Available Low-Dose Capsaicin Supplement on Knee Extensor Contractile Function

Capsaicin, the active pungent ingredient in chili peppers and various spicy foods, is demonstrated to influence a variety of physiological systems including skeletal muscle. The purpose of this study was to examine if a chewable capsaicin supplement (1.2 mg) could enhance isokinetic knee extensor contractile performance. Nine young, recreationally active individuals (5 females/4 males; 23.6 ± 1.5 yrs; 24.2 ± 3.3 kg/m²) participated in this randomized, single-blind crossover study. Following a familiarization session, participants completed two isokinetic knee extensor contractile function assessments, 45 minutes after ingesting either a capsaicin fruit gummy or eucaloric placebo, the order of which was randomized. Knee extensor peak torque (strength), summed torque (endurance) and fatigue index (fatigue) were compared between trials. Knee extensor peak torque was significantly greater (p < 0.05; d = 0.80) in the capsaicin (126.0 ± 40.4 N·m^-1) than the placebo (118.8 ± 41.3 N·m^-1) trial. No significant differences (p > 0.05) were found for summed torque (8012 ± 2771 vs. 7823 ± 2611 N·m^-1; d = 0.45) or fatigue index (56.0 ± 17.1 vs. 48.7 ± 21.0 %; d = 0.46) between capsaicin and placebo trials, respectively. These findings, in a relatively modest and mixed-gender sample, suggest that pre-exercise capsaicin ingestion may benefit knee extensor muscle strength but does not appear to affect parameters of skeletal muscle endurance or fatigue.