Effects of oral capsaicinoids and capsinoids supplementation on resistance and high intensity interval training: A systematic review of randomized controlled trials

Oral capsaicinoids and capsinoids supplementation has been studied recently for a plausible ergogenic impact on sports performance. However, non-aggregated literature has focused on the impact of this substances in healthy humans' performance. The aim of the present systematic review was to explore the effects of capsaicinoids and capsinoids on resistance training (RT) and HIIT exercise. Studies searches were performed in the PubMed/MEDLINE, Scopus and Web of Science electronic databases. Studies where healthy subjects consumed capsaicinoids or capsinoids acutely or chronically compared to placebo before a RT or HIIT intervention were included. The methodological quality of the included studies was assessed with PEDro checklist. A total of 7 excellent-good quality placebo-controlled trials (i.e., 5 RT and 2 HIIT experiments) were included. The most prevalent protocol used capsaicin (i.e., 6 capsacin and 1 capsiate studies) and acute (i.e., 5 of 7 interventions) supplementation designs. Positive effects were only noted for capsaicin in repetitions until failure (+14.4 to +21.7%), total weight lifted (+13.0 to +23.3%), perceived effort (-6.4%), fatigue index (+15.0%) and peak torque (+6.1%) compared to placebo. Neuromuscular HIIT variables (e.g., total and medium sprint time) were not highly affected by capsaicin except the time to reach 90% VO2 peak (+61.2%) and the number of efforts performed (+14.7%). Collectively, our findings suggest a positive effect of 12 mg of capsaicin on strength endurance, total weight lifted and perceived effort variables in healthy males after acute (i.e., 45 minutes pre-exercise) supplementation.