While caffeine is commonly used to help enhance athletic performance, studies regarding the impact of caffeine consumption on muscle strength and power have not been definitive.
As such, researchers at Australia's Victoria University, the University of North Carolina, and Croatia's J.J. Strossmayer University conducted a systematic review and meta-analysis to summarise results from individual studies on the effects of caffeine ingestion on muscle strength and power.
They searched eight databases to locate studies on how caffeine consumption affected maximal muscle strength (measured with one-repetition maximum tests) and muscle power (determined by vertical jump tests).
For their meta-analyses, they used 10 studies on strength outcome, which involved a total of 149 participants (116 male and 33 female), and 10 studies on power outcome, which had a total of 145 participants (116 male and 29 female).
Strength and power
The researchers subsequently found that caffeine intake did improve both muscle strength and power.
They referred to an earlier meta-analysis that had reported caffeine's significant performance-enhancing properties in the Wingate test, a common power test, and added that most of the studies assessed in this current review had used counter-movement jump to assess the study subjects' vertical jump.
They wrote: "It remains to be explored whether caffeine ingestion would produce different effects on other forms of vertical jumping. More evidence may be needed to determine if the performance-enhancing effects of caffeine would transfer in the context of individual sports and / or team-sport matches."
They also performed a sub-group analysis, which suggested that caffeine markedly improves upper but not lower body strength.
This led them to write: "It may be surmised that caffeine is a useful ergogenic aid for achieving acute increases in maximal upper body strength."
They further stated that the expression of strength in the form of 1RM (one-repetition maximum) was most specific to power-lifting but could also translated to enhanced performance in other strength-power sports, as well as sports where jumping is a predominant activity affecting sport-specific performance.
In conclusion, they wrote: "The results of the present meta-analysis are based on limited evidence, and thus need to be interpreted with caution.
"Future studies should more rigorously control the effectiveness of blinding (and) explore the optimal dosage and form of caffeine for maximising effects on strength and power.
"Due to the paucity of evidence, additional findings are needed in the female population and using different forms of caffeine, such as gum and gel.
"Finally, responses to caffeine ingestion have a high degree of inter-individual variability, and as such, the applicability of the current findings must be assessed on a case-by-case basis, based on the specific characteristics of the individual and the sports activity or other physical tasks."
Source: Journal of the International Society of Sports and Nutrition
"Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis"
Authors: Jozo Grgic, et al.