Effect Of Capsaicin And Heavy Resistance Exercise On Ratings Of Perceived Exertion And Muscle Swelling

Capsaicin (CAP), a bioactive compound in chili peppers, activates transient receptor potential vanilloid 1 channels, leading to calcium efflux, which may enhance muscle contraction and make heavy resistance exercises (RE) easier to perform. Additionally, CAP may amplify muscle swelling caused by fluid accumulation during RE due to its mechanistic effects. PURPOSE: Examine the impact of acute CAP ingestion and RE on ratings of perceived exertion (RPE) and muscle swelling in resistance-trained men. METHODS: 10 recreationally resistance-trained men (age: 21 ± 2 years, mass: 79.3 ± 9.9 kg; height: 176.6 ± 6.1 cm) completed 2 identical lower body RE sessions. Participants consumed either 2.4 mg CAP or placebo (PL; microcrystalline cellulose) 45 minutes (m) before RE. Each RE session included 5 sets of 10 repetitions at 80% of 1-repetition maximum on leg press followed by knee extension with 2 weeks separating the conditions. Ratings of perceived exertion (RPE) were recorded after each set, and muscle ultrasounds were taken before RE (PRE), immediately (IP), 10 m, 15 m, and 30 m post-RE to analyze for rectus femoris cross-sectional area (CSA) and thickness (RT). Repeated measures ANOVA were used to analyze the effect of CAP on RPE, CSA, and RT. RESULTS: Results indicated a significant (p < 0.05) condition x set effect for RPE, with PL showing higher RPE (8 ± 0) than CAP (7 ± 0) in the first set. Leg Press exercises (7 ± 0) trended to have lower RPE than knee extensions (8 ± 0; p = 0.07) with CAP. While no significant (p > 0.05) differences were observed between PL and CAP conditions for CSA and RT, both measures increased over time. For CSA, PRE (6.06 ± 0.21 cm2) had a smaller CSA than IP (7.46 ± 0.28 cm2),10 m (7.63 ± 0.23 cm2),15 m (7.33 ± 0.21 cm2), and 30 m (6.95 ± 0.16 cm2) post-RE. For RT, PRE (1.77 ± 0.07 cm) had less thickness than IP (2.33 ± 0.08 cm),10 m (2.29 ± 0.09 cm), 15 m (2.21 ± 0.08 cm), and 30 m (2.09 ± 0.08 cm) post-RE. CONCLUSION: CAP ingestion appears to reduce early RPE during RE, suggesting it may lower initial fatigue and enable a stronger start in high-intensity workouts. CSA and RT increased regardless of supplementation, likely due to similar metabolic stress from the identical RE, which may explain why overall RPE changes were not significant. Future studies should explore CAP's effect on muscle swelling in repetitions performed to failure.