title: 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-1) 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.
authors.affiliation: a Institute of Sport Sciences and Physiotherapy, Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia.
authors.forename: Silva
authors.initials: S
authors.lastname: Suvi
authors.affiliation: a Institute of Sport Sciences and Physiotherapy, Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia.
authors.forename: Saima
authors.initials: S
authors.lastname: Timpmann
authors.affiliation: b Institute of Psychology, Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia.
authors.forename: Maria
authors.initials: M
authors.lastname: Tamm
authors.affiliation: a Institute of Sport Sciences and Physiotherapy, Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia.
authors.forename: Martin
authors.initials: M
authors.lastname: Aedma
authors.affiliation: b Institute of Psychology, Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia.
authors.forename: Kairi
authors.initials: K
authors.lastname: Kreegipuu
authors.affiliation: a Institute of Sport Sciences and Physiotherapy, Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia.
authors.forename: Vahur
authors.initials: V
authors.lastname: Ööpik
mesh_terms: D000328:Adult; D054874:Athletic Performance; D002110:Caffeine / Q000627:therapeutic use*; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D015444:Exercise / Q000523:psychology; D005080:Exercise Test; D017079:Exercise Tolerance; D005221:Fatigue / Q000097:blood / Q000209:etiology / Q000517:prevention & control*; D005260:Female; D006359:Heat Exhaustion / Q000097:blood / Q000209:etiology / Q000517:prevention & control; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D005222:Mental Fatigue / Q000097:blood / Q000209:etiology / Q000517:prevention & control*; D058573:Performance-Enhancing Substances / Q000627:therapeutic use*; D010807:Physical Endurance; D012727:Sex Characteristics; D016138:Walking; D055815:Young Adult
chemical_list: D058573:Performance-Enhancing Substances; D019344:Lactic Acid; D002110:Caffeine
keywords: arousal; effort perçu; fatigue perçue; humeur; mood; perceived exertion; perceived fatigue; performance physique; physical performance; vigilance