|dc.description.abstract||Caffeine is a commonly used drug and can be found in many everyday products. It has been established that caffeine has ergogenic properties in aerobic metabolism; however, the effects of caffeine on anaerobic metabolism are still unclear in respect to performance and muscle recovery and some data suggest caffeine may even have inhibitory effects on muscle growth. The purpose of this research was to document the effects of caffeine intake on muscle protein synthesis rates, muscle performance, and changes in lean mass following resistance exercise training. We hypothesized that increased caffeine intake would cause a decrease in muscle protein synthesis rates.
The first study examined the effect of caffeine on rates of muscle protein synthesis rates following an acute bout of resistance exercise in male Sprague Dawley rats. Caffeine intake did not alter the rates of muscle protein synthesis following resistance exercise.
The second study examined muscle protein synthesis rates following resistance exercise in men consuming a caffeine bolus before exercise. Muscle performance was measured using maximal power, total weight, and total repetitions. Activation of cellular proteins (AMPK and p70s6) was measured by Western Blots. Caffeine intake had no effect on 24-hour muscle protein synthesis, power output, and total weight and repetitions performed. There were also no differences in total p70s6K, phosphorylated p70s6K, or phosphorylated AMPK between groups, but an increase in total AMPK expression was observed.
The final study analyzed the effects of habitual caffeine intake on changes in lean mass and muscle performance following 12 weeks of full-body resistance exercise in an untrained population. There were no changes in lean mass; however, the data suggested that high caffeine intake was associated with lower muscle performance in certain exercises (leg press, leg curl, and lat pulldown) and not in others (chest press, bicep curl, leg extension, and triceps extension).
The results of these studies suggest that caffeine intake has no effects on muscle protein synthesis following acute resistance exercise and no effect on changes in lean mass following chronic resistance exercise. Future studies involving different populations and exercise models may clarify the effects of caffeine on exercise performance.||