Middle distance running (i.e., 1,500 m), when performed at maximal efforts, requires substantial aerobic and anaerobic metabolic contribution (2,38). In addition, it seems that 1,500-m running performance is dependent on a runner's ability to maintain pace for a longer duration at the anaerobic power threshold to avoid a reduction in running speed (1,3). Muscular fatigue is the most likely limiting factor that affects middle distance running performance (9,10,29) because low creatine phosphate availability and accumulation of hydrogen ions, inorganic phosphate, and reactive oxygen species, and the onset of acidosis reduce calcium release by the sarcoplasmic reticulum (5,19,25,30), resulting in decreased force production of skeletal muscle (11,21).
Several studies have been conducted to find nutrients that enhance middle distance running performance in humans (6,32,35). Capsaicin (8-methyl-N-vanillyl-trans-6-nonenamide) is a major pungent and bioactive phytochemical found primarily in chili peppers and other spicy foods (23). Capsaicin is a strong agonist of the transient receptor potential vanilloid-1 (TRPV1) in many organs, leading to the sensation of heat, activation of the sympathetic nervous system (33,36), and potentially increasing lipolysis, fatty acid oxidation, and energy expenditure (13,15,23). Capsaicin has been studied as a potential antiobesity agent in humans and animals, with several studies demonstrating positive results (20,34,37).
Capsaicin has been investigated to improve exercise performance, although most studies related to performance have been conducted in rodents. Luo et al. (24) showed that capsaicin promoted mitochondrial biogenesis, increased cytosolic free calcium in myotubes, and enhanced endurance in mice. Kim et al. (16) found that capsaicin supplementation (10–15 mg·kg−1·d−1) increased swimming time until exhaustion in mice. Oh and Ohta (27) demonstrated that capsaicin improved endurance capacity and spares tissue glycogen in swimming rats. Lotteau et al. (22) reported that capsaicin induces the activation of TRPV1 receptor in skeletal muscle and increases the release of calcium by the sarcoplasmic reticulum. Fatiguing exercise reduces the rate of calcium release in sarcoplasmic reticulum vesicles (19), which has been shown to contribute to reductions in myofiber force generation (21); therefore, an increase of intracellular calcium by capsaicin may result in an enhanced interaction between actin-myosin filaments and result in greater force output and improved endurance.
Although several studies have been conducted investigating the effects of capsaicin on energy expenditure, lipolysis, and fat loss in humans (13,33,34), the effects of capsaicin on performance in humans is limited. Our group recently demonstrated that acute capsaicin supplementation (12 mg) increased resistance exercise (4 sets until muscular failure with 70% of 1 repetition maximum in squat exercise) performance and decreased RPE in trained men (7). However, Opheim and Rankin (28) investigated 28.5 mg of capsaicin ingested through 3 g of powdered Capsicum frutescens (cayenne pepper) capsules for 7 days. Capsaicin supplementation did not enhance repeat sprint ability (15 × 30-m sprints with 35-second intervals) in healthy athletes. A single dose of both 10 and 100 mg·kg−1 capsaicin was recently shown to reduce the ATP cost during 6 minutes of repeated fatiguing isometric contractions with the higher dose also increasing force-generating capabilities in mouse skeletal muscle (14). However, the effects of capsaicin on performance in humans during a similar duration of work as well as how capsaicin affects RPE and lactate during middle distance running currently require investigation.
The purpose of this study is to investigate the acute effect of capsaicin supplementation on 1,500-m running time-trial performance, RPE, and blood lactate concentrations in physically active adults. We hypothesized that capsaicin consumption would enhance performance during 1,500-m running and induce a lower RPE and blood lactate concentration.
Experimental Approach to the Problem
This study used a randomized, double-blind, crossover design depicted in Figure 1. Subjects completed 2 experimental trials, performed at the same time of day (7–8 am), which were separated by 1 week. During the first visit, measurements of anthropometrics and body composition were performed. On the following 2 visits, each participant consumed randomly either the placebo or capsaicin and then completed a 1,500-m run. Blood lactate was analyzed and RPE was collected after exercise.
Ten physically active men were recruited for this study (± SD age = 23.5 ± 1.9 years; height = 177.9 ± 5.9 cm; mass = 78.3 ± 12.4 kg ± SD; and percentage of fat mass = 14.6 ± 3.0%). Inclusion criteria for participation in the study were: not participating in regimented running training during the previous 6 months; between 20 and 30 years age; no contraindications involving the cardiovascular system, muscles, joints, or bones of the lower limbs that might interfere with the exercise protocol; and, not taking any performance-enhancing supplements or ergogenic substance during the previous 6 months, and not smoking. During the study, all participants were instructed not to use any other supplement or ergogenic substance as well as make changes to their regular diet and exercise. This study was approved by the Ethics Research Group of the University of São Judas, São Paulo, Brazil. All participants were 18 years or older and signed a consent form and were informed about the purpose of the study and the possible risks.
Anthropometric Measurements, Body Composition, and Dietary Intake Assessment
Height was measured on a fixed stadiometer of the Sanny brand, with an accuracy of 0.1 cm and a length of 2.20 m. Body weight was measured using an electronic scale (Filizola PL 50; Filizola, Ltda., São Paulo, Brazil), with a precision of 0.1 kg. Bioimpedance analysis (BIA) was performed using a single-frequency 50-kHz analyzer (BIA Analyzer-101Q; RJL Systems, Detroit, EUA). Measurements were obtained from the right hand and right foot. After recording values of resistance (R) and reactance (Xc), estimates of FFM and FM were obtained from sex-specific BIA prediction equations developed for college men aged between 18 and 30 years: FFM = (10.97556) − (0.03187) × (R) + (0.17576) × (Height) + (0.50702) × (Weight) and we presented percentage of fat mass (%). The equation showed correlation coefficient (r = 0.96) and standard error of estimation (SEE = 2.0) (Rodrigues de Carvalho and Pires Neto, 1998).
The volunteers were instructed not to consume chili peppers or other spicy foods as well as coffee, tea, alcohol or stimulant drinks for a period of 12 hours before the assessment. Food questionnaires were distributed to all participants to record food and fluid intake for 24 hours before each trial in addition to their pre-exercise meal (breakfast). The participants were instructed to consume breakfast at their homes an hour and a half before each experimental trial and to replicate the first trial's dietary intake for the subsequent trial. All food intakes were analyzed for total kilocalorie and macronutrient intakes (Software—Dietpro version 5.8) to ensure that dietary intake was similar between experimental trials. The software used the database of Brazilian food composition table (TACO) to calculate dietary intake.
A previous pilot study was performed with 4 subjects to identify sensations associated with capsaicin ingestion. The form and dose of capsaicin in this study was well tolerated and none of the subjects reported any “hot” sensations or gastrointestinal distress.
On the exercise testing sessions, each participant randomly consumed either the placebo (50 mg of starch) or 12 mg of purified capsaicin (Pharma Nostra, Campinas, Brazil). This dosage was selected because other studies have reported that supplementation of more than 33 mg per day of capsaicinoid increases gastric motility (36). The capsules were identical to ensure a double-blind design. Capsaicin or placebo were ingested 45 minutes before the experimental test. This timing was selected because capsaicin reaches peak concentrations 45 minutes after supplementation (4), the half-life of capsaicin is approximately 25 minutes, and full clearance from the plasma occurs approximately 105 minutes after supplementation (31).
Rate of Perceived Exertion and Blood Lactate Concentration
The RPE was measured after exercise session using the 6–20 point Borg scale. Blood samples were collected from the ear lobe of each participant to analyze the lactate concentration. This measurement was obtained at rest, immediately after running time trial, post-5 minutes, post-10 minutes, and post-30 minutes during the recovery. The blood lactate analysis was performed using the Yellow Spring 1500 Sport lactimeter (Yellow Springs, OH, USA).
Middle Distance Running Time-Trial Protocol
Before each testing session participants completed a 10-minute warm-up (5 minutes of stretching and 5 minutes of jogging). The participants performed 1,500 m on an outdoor track (400 m) separated by 7 days. The participants were tested one at a time and were instructed to cover the distance in the shortest possible time, which was recorded using a digital stopwatch (Polar). Participants were instructed to wear the same kind of clothes (light shorts, light t-shirts, and running shoes) in each test. All tests were conducted in the same day at the same hour (7–8 am) and all the tests were conducted when the following climate values were presented: temperature (23–25° C), humidity (65–70%), and wind speed (19–21 km·h−1). Four fitness professionals supervised all testing sessions.
The data normality was verified using the Shapiro-Wilk test. The comparison of the performance and RPE under the different conditions was analyzed using a repeated-measures t-test. A 2 × 5 repeated-measures analysis of variance with the Bonferroni adjustment for multiple comparisons was used to compare lactate concentration across conditions and time, respectively. For all measured variables, the estimated sphericity was verified according to Mauchly's W test and the Greenhouse-Geisser correction was used when necessary. Statistical significance was set at p ≤ 0.05. The effect size was calculated using Cohen's d and whereby a value of >0.20 was considered small, >0.50 moderate, and >0.80 large, and the partial eta-squared (η2) was calculated when necessary. The data were analyzed using the Statistical Package for the Social Sciences 17.0 (SPSS, Inc., Chicago, IL, USA).
Table 1 presents the mean and SD values for dietary intake and macronutrient distribution of the sample 24 hours before each trial and pre-exercise meal (breakfast).
Figure 2 displays the differences in performance for the capsaicin and placebo condition and Figure 3 shows the RPE for both conditions.
The time in seconds was significantly (t = 3.316, p = 0.009) less in the capsaicin (371.6 ± 40.8 seconds) compared with the placebo (376.7 ± 39 seconds) condition. Rate of perceived exertion was significantly (t = 2.753, p = 0.022) less in the capsaicin (18.0 ± 1.9) compared with the placebo (18.8 ± 1.3) condition.
Figure 4 shows the differences in lactate concentrations across time and between conditions.
There was a main effect of time (F = 108.52, p < 0.001). Lactate increased across time for both conditions without significant difference between conditions or an interaction.
To the best of our knowledge, this was the first study to investigate the effects of 12 mg of capsaicin supplementation on performance, RPE, and blood lactate concentrations during 1,500-m time-trial run in physically active men. The main findings of this study were that acute capsaicin supplementation decreased 1,500-m time and resulted in a lower RPE.
Currently, there is a lack of studies investigating the effects of capsaicin supplementation on exercise performance in humans. Several studies conducted in rodents have observed an increased time until exhaustion during swimming and reported a concomitant sparing of tissue glycogen in rats (16,17,27). Hsu et al. (12) investigated the effects of capsaicin supplementation during 4 weeks on endurance performance and forelimb grip strength in mice. The results showed that grip strength and exhaustive swimming time were significantly higher with capsaicin supplementation. Capsaicin reduced serum lactate, ammonia, blood urea nitrogen, and creatine kinase levels after swimming exercise. By contrast, in this study, subjects decreased 1,500-m run time by approximately 5 seconds when compared with placebo without changes in lactate concentrations between conditions.
In humans, Opheim and Rankin (28) found that 7 days of capsaicin supplementation (25.8 mg·d−1) did not enhance repeat sprint performance (15 × 30-m sprints with 35-second intervals) in athletes. The discrepancy between the Opheim and Rankin's study and this study could be due to the form of the capsaicin supplement (pure capsaicin vs. cayenne pepper), dosage (12 vs. 25.8 mg), or the exercise task tested. Opheim and Rankin reported that cayenne pepper supplementation induced gastrointestinal discomfort in 25% of subjects, which may have affected the results. In this study, the dose and form of capsaicin was well tolerated in all subjects and was associated with a lower RPE compared with placebo. In accord with these results, we recently found that capsaicin (12 mg) improved total weight lifting in conjunction with a lower RPE during 4 sets of back squats to fatigue (7).
The potential mechanisms by which capsaicin may improve performance are likely a result of TRPV1 activation. First, capsaicin may have enhanced performance by analgesic effects (8). The activation of TRPV1 receptor by capsaicin can generate analgesic effects by inactivating the primary nerve endings because of calcium overload (18). We found a lower RPE for the capsaicin condition in this study. It is possible that capsaicin supplementation may have increased the pain threshold and reduced discomfort induced by fatiguing exercise, thereby resulting in improved running times; however, more research is needed to substantiate this hypothesis. Second, it has been reported that muscular fatigue is a result, at least in part, of high concentrations of hydrogen, inorganic phosphate, and reactive oxygen species that reduces the capacity of sarcoplasmic reticulum calcium release (5,19,30), thereby decreasing muscle contraction efficiency and myofiber force generation (11,21). Activation of TRPV1 by capsaicin can also modulate the calcium channel in skeletal muscles, thereby increasing calcium release by sarcoplasmic reticulum and potentially resulting in attenuated force production (22). Finally, the improvement in endurance performance in rodents is partially attributed to a muscle glycogen sparing effect, as a result of higher lipolysis by greater release of epinephrine, norepinephrine, and free fatty acids during exercise (17). Because there were no differences between conditions in lactate concentrations and the short duration of the exercise, a sparing of muscle glycogen was likely not a factor that contributed to enhanced performance in this study. However, we were unable to measure free fatty acids or muscle glycogen, and therefore, more research is necessary to investigate the metabolic effects of capsaicin supplementation during exercise.
Some limitations must be considered when interpreting and applying the results of this study. First, the subjects in this study were physically active, but not highly trained. Given that 5 seconds separated the 1st and 15th places at the 2017 men's NCAA Division 1 1,500-m championships (26), more research is needed to examine the effects of acute capsaicin supplementation on trained middle distance runners before capsaicin can be suggested to athletes. Second, we were unable to measure catecholamines, glycemia, or respiratory quotient in this study. Given a glycogen sparing effect of capsaicin supplementation reported in rodent models, further research should investigate the effects of capsaicin supplementation on long distance running protocols, whereby glycogen depletion is a major contributor to fatigue. In addition, further studies are necessary to measure the catecholamine response and energy system contributions in humans.
In summary, acute capsaicin supplementation improved middle distance running performance and reduced RPE in physically active adults.
This study suggests that acute capsaicin supplementation can be used as a nutritional strategy to improve performance during 1,500-m running by lowering RPEs. The dose and form of capsaicin used was well tolerated and the results of this study may be applied by coaches and trainers looking to improve performance in amateur runners.
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