Caffeine intake improves intense intermittent exercise performance and reduces muscle interstitial potassium accumulation.
Study Goal
The researchers aimed to determine the effects of caffeine on intense intermittent exercise performance and muscle interstitial ion concentrations.
Results Summary
Caffeine improved Yo-Yo IR2 performance by 16% and reduced muscle interstitial K(+) during intense exercise, while increasing plasma free fatty acids, blood glucose, and plasma NH(3). No differences in interstitial Na(+) were observed.
Population
12 subjects in S1 (Yo-Yo IR2 test), 6 subjects in S2 (knee-extension exercise)
Effective Dosage
6 mg/kg body weight
Duration
Single-dose intervention
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
oral caffeine ingestion | increase | fatigue resistance | - | - | enhances | #1 |
oral caffeine ingestion | decrease | muscle interstitial K(+) | - | - | reduces | #2 |
caffeine (6 mg/kg body wt; CAF) | increase | Yo-Yo IR2 performance | 12 subjects | 16% | was 16% better | #3 |
caffeine (6 mg/kg body wt; CAF) | no change | plasma K(+) at the end of the Yo-Yo IR2 test | 12 subjects | 5.2 ± 0.1 mmol/l | no difference | #4 |
caffeine (6 mg/kg body wt; CAF) | increase | plasma free fatty acids (FFA) | 12 subjects | - | were higher | #5 |
caffeine (6 mg/kg body wt; CAF) | increase | peak blood glucose | 12 subjects | 8.0 ± 0.6 vs. 6.2 ± 0.4 mmol/l | were higher | #6 |
caffeine (6 mg/kg body wt; CAF) | increase | plasma NH(3) | 12 subjects | 137.2 ± 10.8 vs. 113.4 ± 13.3 μmol/l | were higher | #7 |
prior caffeine supplementation (CAF) | decrease | interstitial K(+) at the end of the 20-W and three 50-W periods | 6 subjects | 5.5 ± 0.3, 5.7 ± 0.3, 5.8 ± 0.5, and 5.5 ± 0.3 mmol/l vs. 7.0 ± 0.6, 7.5 ± 0.7, 7.5 ± 0.4, and 7.0 ± 0.6 mmol/l | were lower | #8 |
prior caffeine supplementation (CAF) | no change | interstitial Na(+) | 6 subjects | - | No differences | #9 |
The effect of oral caffeine ingestion on intense intermittent exercise performance and muscle interstitial ion concentrations was examined. The study consists of two studies (S1 and S2). In S1, 12 subjects completed the Yo-Yo intermittent recovery level 2 (Yo-Yo IR2) test with prior caffeine (6 mg/kg body wt; CAF) or placebo (PLA) intake. In S2, 6 subjects performed one low-intensity (20 W) and three intense (50 W) 3-min (separated by 5 min) one-legged knee-extension exercise bouts with (CAF) and without (CON) prior caffeine supplementation for determination of muscle interstitial K(+) and Na(+) with microdialysis. In S1 Yo-Yo IR2 performance was 16% better (P < 0.05) in CAF compared with PLA. In CAF, plasma K(+) at the end of the Yo-Yo IR2 test was 5.2 ± 0.1 mmol/l with no difference between the trials. Plasma free fatty acids (FFA) were higher (P < 0.05) in CAF than PLA at rest and remained higher (P < 0.05) during exercise. Peak blood glucose (8.0 ± 0.6 vs. 6.2 ± 0.4 mmol/l) and plasma NH(3) (137.2 ± 10.8 vs. 113.4 ± 13.3 μmol/l) were also higher (P < 0.05) in CAF compared with PLA. In S2 interstitial K(+) was 5.5 ± 0.3, 5.7 ± 0.3, 5.8 ± 0.5, and 5.5 ± 0.3 mmol/l at the end of the 20-W and three 50-W periods, respectively, in CAF, which were lower (P < 0.001) than in CON (7.0 ± 0.6, 7.5 ± 0.7, 7.5 ± 0.4, and 7.0 ± 0.6 mmol/l, respectively). No differences in interstitial Na(+) were observed between CAF and CON. In conclusion, caffeine intake enhances fatigue resistance and reduces muscle interstitial K(+) during intense intermittent exercise.