Placebo in sports nutrition: a proof-of-principle study involving caffeine supplementation.
Study Goal
The researchers aimed to determine whether participants' identification of caffeine supplementation influenced its effects on exercise performance in trained cyclists.
Results Summary
Caffeine significantly improved cycling performance compared to placebo and control, with greater improvements when participants correctly identified caffeine. Belief in caffeine ingestion also showed a tendency to enhance performance, while correct placebo identification had possible harmful effects.
Population
42 trained cyclists (age 37 ± 8 years, body mass 74.3 ± 8.4 kg, height 1.76 ± 0.06 m, maximum oxygen uptake 50.0 ± 6.8 mL/kg/min).
Effective Dosage
6 mg/kg body mass caffeine, single dose.
Duration
Single session (~30 min cycling time-trial 1 h post-supplementation).
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
6 mg/kgBM caffeine (CAF) | increase | exercise performance | trained cyclists | - | improved performance | #1 |
caffeine | increase | exercise performance | participants who correctly identified caffeine pre-exercise | +4.8% | improved exercise performance | #2 |
caffeine | increase | exercise performance | participants who correctly identified caffeine post-exercise | +6.5% | improved exercise performance | #3 |
caffeine | increase | exercise performance | overall | +4.1% | improved exercise performance | #4 |
placebo (PLA) | no change | exercise performance | within subgroups | - | performance was not different | #5 |
placebo | increase | exercise performance | participants who believed they had ingested caffeine post-exercise | 87% likely beneficial | tendency toward improved performance | #6 |
placebo | decrease | exercise performance | participants who correctly identified placebo in PLA | - | showed possible harmful effects on performance | #7 |
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.