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

Abstract

Objective: Phenylcapsaicin (PC) is a new capsaicin analog which has exhibited a higher bioavailability. This sudy assessed the effects of a low dose (LD) of 0.625 mg and a high dose (HD) of 2.5 mg of PC on aerobic capacity, substrate oxidation, energy metabolism and exercise physiological variables in young males. Materials and methods: Seventeen active males (age = 24.7 ± 6.0 years) enrolled to this randomized, triple-blinded, placebo-controlled, crossover trial. Participants attended the laboratory on 4 sessions separated by 72-96 h. A submaximal exercise test [to determine maximal fat oxidation (MFO) and the intensity at MFO (FATmax)] followed by a maximal incremental test (to determine VO2_max) were performed in a preliminary session. The subsequent sessions only differed in the supplement ingested [LD, HD or placebo (PLA)] and consisted of a steady-state test (60 min at FATmax) followed by a maximal incremental test. Energy metabolism, substrate oxidation, heart rate, general (gRPE) and quadriceps (RPEquad) rate of perceived exertion, skin temperature and thermal perception were tested. Results: Clavicle thermal perception was lower in HD compared to PLA and LD (p = 0.04) across time. HD reduced maximum heart rate in comparison to PLA and LD (p = 0.03). LD reported higher general RPE (RPEg) values during the steady-state test compared to PLA and HD across time (p = 0.02). HD and LD elicited higher peak of fat oxidation during the steady-state test compared with PLA (p = 0.05). Intra-test analyses revealed significant differences for fat oxidation (FATox) in favor of HD and LD compared to PLA (p = 0.002 and 0.002, respectively), and for carbohydrate oxidation (CHOox) (p = 0.05) and respiratory exchange ratio (RER) (p = 0.03) for PLA. In the incremental test, only general RPE at 60% of the maximal intensity (W) differed favoring HD (p ≤ 0.05). Conclusion: Therefore, PC may contribute to increase aerobic capacity through the improvement of fat oxidation, maximum heart rate and perceptual responses during exercise.

Keywords: ergogenic aid; exercise capacity; exercise metabolism; phenylcapsaicin; substrate oxidation.

FIGURE 1

General overview of the study (A) and design of the experimental sessions (B) aiming to analyze the effects of two doses of phenylcapsaicin on metabolic, thermal, perceptual, and mechanical responses to steady-state and maximal cycling tests. HD, high dose; LD, low dose; PLA, placebo; HR, heart rate; RGE, respiratory gas exchange; RPEg, general ratings of perceived exertion; RPEquad, ratings of perceived exertion of quadriceps; SS, steady-state. Created with BioRender.com.

FIGURE 2

Two-way repeated measures analysis of variance (ANOVA) comparing the effects of consuming different dosis of phenylcapsaicin (HD and LD) or placebo (PLA) on thermal perception (ASHRAE scale) at different time points. PLA, Placebo; HD, High dose; LD, Low dose; PC, Phenylcapsaicin. PRE: Before the start of the session; Post 1: Between the steady state test and maximal effort test; Post 2: After the maximal effort test.

FIGURE 3

Two-way repeated measures analysis of variance (ANOVA) comparing the effects of phenylcapsaicin and placebo (PLA, HD, LD) across time on substrate oxidation, energy expenditure and respiratory exchange ratio during the 60 min steady-state test. AUC, Area Under the curve; FATox, Fat oxidation; CHOox, Carbohydrates oxidation; EE, Energy expenditure; RER, Respiratory exchange ratio; PLA, Placebo; HD, High dose; LD, Low dose; PC, Phenylcapsaicin. Intra-test analysis (one-way repeated measures ANOVA): *p _ANOVA ≤ 0.05; #p _Bonferroni ≤ 0.05.