Effects of caffeine on endurance capacity and psychological state in young females and males exercising in the heat

Abstract

Acute caffeine ingestion is considered effective in improving endurance capacity and psychological state. However, current knowledge is based on the findings of studies that have been conducted on male subjects mainly in temperate environmental conditions, but some physiological and psychological effects of caffeine differ between the sexes. The purpose of this study was to compare the physical performance and psychological effects of caffeine in young women and men exercising in the heat. Thirteen male and 10 female students completed 2 constant-load walks (60% of thermoneutral peak oxygen consumption on a treadmill until volitional exhaustion) in a hot-dry environment (air temperature, 42 °C; relative humidity, 20%) after caffeine (6 mg·kg) and placebo (wheat flour) ingestion in a double-blind, randomly assigned, crossover manner. Caffeine, compared with placebo, induced greater increases (p < 0.05) in heart rate (HR) and blood lactate concentrations in both males and females but had no impact on rectal or skin temperatures or on walking time to exhaustion in subjects of either gender. Caffeine decreased (p < 0.05) ratings of perceived exertion and fatigue in males, but not in females. In females, but not in males, a stronger belief that they had been administered caffeine was associated with a shorter time to exhaustion. In conclusion, acute caffeine ingestion increases HR and blood lactate levels during exercise in the heat, but it has no impact on thermoregulation or endurance capacity in either gender. Under exercise-heat stress, caffeine reduces ratings of perceived exertion and fatigue in males but not in females.

Effect of Caffeine Supplementation on Sports Performance Based on Differences Between Sexes: A Systematic Review

“…The total sample consisted of 221 participants ( n = 113 males; n = 108 females) [29,30,31,32,33,34,35,36,37,38]. All studies were performed using adult populations.…”

“…All studies were performed using adult populations. Healthy active students were selected in three studies [30,31,37] while the remaining studies included participants catalogued as athletes because they train for a specific sport. Athletes from endurance sports such as cycling, triathlon [29,32,36], and from resistance training modalities were used in the investigations [35,38].…”

“…The sources of caffeine supplementation were varied, including commercial drinks used by Jacobson et al (2018) [37], Tinsley et al (2017) [35], high chlorogenic coffee (Turkish coffee) used by Nieman et al (2017) [32], dry anhydrous caffeine mixed with 300 mL water and a sugar-free peach squash solution proposed by Sabblah et al (2015) [38], and caffeine gum used by Paton et al (2015) [29]. The other authors of this systematic review used capsules to administer the scheduled doses of caffeine in their studies [31,33,34,36].…”

“…In this respect, studies conducted with the general population have already shown that the stimulating effects (less drowsiness and greater activation) of caffeine are greater in men than in women [28]. Still, few studies have shown the differences in the effect of caffeine supplementation on sports performance between men and women, and their results are controversial [29,30,31,32,33,34,35,36,37]. While some studies have shown a comparable ergogenic effect of caffeine between sexes on sports performance, others have presented a greater effectiveness of caffeine to increase sprint power [29], isolated forehand stroke peak and average speed [37], total weight lifted [38] and a shorter time to perform a repeated modified agility test (RMAT) [30] in men compared to women.…”

Caffeine and Exercise: What Next?

“…Several studies compare the effects of caffeine amongst males and females, reporting similar effects in both sexes [ 121 – 123 ], outlined in Table 3 . Whilst other studies have recruited both sexes, they generally analyzed males and females together [ 107 , 124 ].…”