title: Placebo in sports nutrition: a proof-of-principle study involving caffeine supplementation.
abstract: We investigated the effects of supplement identification on exercise performance with caffeine supplementation. Forty-two trained cyclists (age 37 ± 8 years, body mass [BM] 74.3 ± 8.4 kg, height 1.76 ± 0.06 m, maximum oxygen uptake 50.0 ± 6.8 mL/kg/min) performed a ~30 min cycling time-trial 1 h following either 6 mg/kgBM caffeine (CAF) or placebo (PLA) supplementation and one control (CON) session without supplementation. Participants identified which supplement they believed they had ingested ("caffeine", "placebo", "don't know") pre- and post-exercise. Subsequently, participants were allocated to subgroups for analysis according to their identifications. Overall and subgroup analyses were performed using mixed-model and magnitude-based inference analyses. Caffeine improved performance vs PLA and CON (P ≤ 0.001). Correct pre- and post-exercise identification of caffeine in CAF improved exercise performance (+4.8 and +6.5%) vs CON, with slightly greater relative increases than the overall effect of caffeine (+4.1%). Performance was not different between PLA and CON within subgroups (all P > 0.05), although there was a tendency toward improved performance when participants believed they had ingested caffeine post-exercise (P = 0.06; 87% likely beneficial). Participants who correctly identified placebo in PLA showed possible harmful effects on performance compared to CON. Supplement identification appeared to influence exercise outcome and may be a source of bias in sports nutrition.
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: B
authors.initials: B
authors.lastname: Saunders
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: L F
authors.initials: LF
authors.lastname: de Oliveira
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: R P
authors.initials: RP
authors.lastname: da Silva
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: V
authors.initials: V
authors.lastname: de Salles Painelli
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: L S
authors.initials: LS
authors.lastname: Gonçalves
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: G
authors.initials: G
authors.lastname: Yamaguchi
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.
authors.forename: T
authors.initials: T
authors.lastname: Mutti
authors.affiliation: Rheumatology Division, School of Medicine, University of São Paulo, Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Maciel
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.|Rheumatology Division, School of Medicine, University of São Paulo, Brazil.
authors.forename: H
authors.initials: H
authors.lastname: Roschel
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.|Rheumatology Division, School of Medicine, University of São Paulo, Brazil.
authors.forename: G G
authors.initials: GG
authors.lastname: Artioli
authors.affiliation: Applied Physiology & Nutrition Research Group, University of São Paulo, Brazil.|Rheumatology Division, School of Medicine, University of São Paulo, Brazil.
authors.forename: B
authors.initials: B
authors.lastname: Gualano
mesh_terms: D000328:Adult; D054874:Athletic Performance; D001642:Bicycling / Q000502:physiology*; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D019587:Dietary Supplements; D004311:Double-Blind Method; D005080:Exercise Test; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D058573:Performance-Enhancing Substances / Q000008:administration & dosage / Q000494:pharmacology*; D000075082:Proof of Concept Study; D064133:Sports Nutritional Physiological Phenomena
chemical_list: D058573:Performance-Enhancing Substances; D002110:Caffeine
keywords: Placebo effect; caffeine supplementation; cycling time-trial; exercise performance; expectancy; nocebo effect; supplement identification