Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Page numbers: 282-290
doi (if applicable): 10.1249/MSS.0b013e3181e3a11d
Summary of Background and Research Design
Background: Caffeine has consistent ergogenic effects in high-intensity aerobic activities such as swimming, cycling, and exercising to exhaustion, but only approximately 60% of studies show caffeine to be beneficial in activities involving anaerobic power.
Hypothesis/Research Question: What is the effect of a low (2 mg/kg) or high (5 mg/kg) dose of caffeine vs. a placebo on fatiguing knee extension/flexion exercise?
Subjects: 15 recreationally active men that routinely consume >100 mg caffeine/day
Experimental design: Single-blind, randomized, counterbalanced, cross-over design
Treatments and protocol:
Treatments consisted of 0, 2 mg/kg or 5 mg/kg caffeine in a package with noncaloric, lemon flavored Crystal Light. Subjects were asked to refrain from caffeine and intense exercise 48 hrs prior to the exercise protocols.
Subjects first underwent a familiarization trial. They performed 40 repetitions of knee extension/flexion on their dominant leg at a velocity equal to 180°/sec where they were instructed to use maximal effort. For exercise trials, subjects dissolved the treatment powder in 8 oz of water and drank it 1 hr prior to the trial. Participants warmed up for 5 min on a stationary cycle. They then completed 40 repetitions of knee extension/flexion exercises on the dominant leg at maximal effort, rested for 3 min, and then repeated the knee extension/flexion exercises. Peak and average torque (ft?lb), power (W), total work (ft?lb), and work fatigue (%) were recorded for both bouts. Rating of perceived exertion (RPE) was assessed with a 10-point Borg scale 25 repetitions into the exercise bout.
Summary of Research Findings
A 5 mg/kg dose of caffeine increased total work output for leg extension exercise compared with the 2 mg/kg and the placebo in bout 1 but not bout 2 (p<0.05). A 5 mg/kg dose of caffeine increased total work output for leg flexion exercise over the placebo also only for bout 1 (p<0.05). Similarly, the 5-mg/kg dose, compared with placebo, increased power output in the leg extension phase for bout 1 but not bout 2. No treatment effect for was noted for peak or average torque, work fatigue, or rating of perceived exertion.
Interpretation of findings/Key practice applications:
Large doses of caffeine (5 mg/kg) can function as an ergogenic aid for anaerobic, power-related exercises. Because the differences were only statistically significant in bout 1, this implies that caffeine may exert most of its benefits before the muscle is largely fatigued.
The results of this study only apply to anhydrous caffeine supplementation. It is not clear if the same benefits would have been achieved with coffee or other caffeinated beverages.