Effects of different phenylcapsaicin doses on resistance training performance, muscle damage, protein breakdown, metabolic response, ratings of perceived exertion, and recovery: a randomized, triple-blinded, placebo-controlled, crossover trial

Abstract

Background The aim of this study was to explore the effects of a low dose (LD) of 0.625 mg and a high dose (HD) of 2.5 mg of phenylcapsaicin (PC) on full squat (SQ) performance, active muscle (RPE-AM) and overall body (RPE-OB) ratings of perceived exertion, muscle damage, protein breakdown, metabolic response, and 24-h recovery in comparison to placebo (PLA). Method Twenty-five resistance-trained males (age = 21.00 ± 2.15 years, SQ 1-repetition maximum [1RM] normalized = 1.66 ± 0.22 kg) were enrolled in this randomized, triple-blinded, placebo-controlled, crossover trial. Participants completed 2 weekly sessions per condition (LD, HD, and PLA). The first session consisted of pre-blood testing of lactate, urea, and aspartate aminotransferases (AST) and 2 SQ repetitions with 60% 1RM followed by the resistance exercise protocol, which consisted of SQ sets of 3 × 8 × 70% 1RM monitoring lifting velocity. RPE-OB and RPE-AM were assessed after each set. After the first session, 2 SQ repetitions with 60% 1RM were performed, and blood lactate and urea posttests were collected. After 24 h, AST posttest and 1 × 2 × 60% 1RM were determined as biochemical and mechanical fatigue outcomes. Results HD reported significant differences for RPE-AM, AST, and SQ performance compared to LD and PLA. Post-hoc analyses revealed that HD attained faster velocities in SQ than LD ( p = 0.008). HD induced a lower RPE-AM when compared with LD ( p = 0.02) and PLA ( p = 0.004). PLA resulted in higher AST concentrations at 24-h post than HD ( p = 0.02). No significant differences were observed for the rest of the comparisons. Conclusions This study suggests that PC may favorably influence SQ performance, RPE-AM, and muscle damage compared to PLA. However, HD exhibited most of the biochemical and mechanical anti-fatigue effects instead of LD.

Effects of phenylcapsaicin on aerobic capacity and physiological parameters in active young males: a randomized, triple-blinded, placebo-controlled, crossover trial

“…However, contrary to previous research where capsaicin supplementation led to lower RPE values, in our data, participants showed higher RPE scores under the LD condition, and improvements were not reported with HD compared to PLA ( de Freitas et al, 2018a ). The low intensity demanded in this task may be insufficient to report an ergogenic effect of PC on perceptual variables ( Jiménez Martínez et al, 2023 ). However, LD of PC reported for the first time a worsening effect of a capsaicinoid on RPE.…”

“…TRPV1 are linked to afferent III and IV nerve fibers ( Collins et al, 2018 ). These fibers influence central fatigue during exercise, which finally reduce motorneuron firing during high-intensity tasks ( Alix-Fages et al, 2022b ; Jiménez Martínez et al, 2023 ). For this reason, HD might have produce a “desensitizer” effect leading to a lower percepetion of exertion in the maximal incremental test.…”