Effects of caffeine on muscle strength: Influence of genetics

Research into whether caffeine is ergogenic for muscle strength is uncertain at present. Furthermore, recent research has emerged suggesting that single nucleotide polymorphisms (SNPs) may influence caffeine response variation, thus influencing performance. Further research on these topics is required to conclude whether caffeine is ergogenic for muscle strength, and whether genotype influences the ergogenicity of caffeine. PURPOSE: To investigate the effects of caffeine (5 mg∙kg-1) on muscle strength, muscle activity and neuromuscular function. To also investigate the effects of genotypes (AA or AC/CC) in the CYP1A2 gene on the aforementioned measures. METHODS: Using a double-blind, randomised, repeated crossover design, 16 participants (11 male, 5 female) completed four experimental trials; two caffeine, two placebo, in which muscle strength, muscle activity and neuromuscular function was assessed. Participants were also categorised according to their genotype (AA or AC/CC). RESULTS: Caffeine significantly increased hand grip strength (P = 0.004), voluntary activation (VA) (P = 0.002) and peak surface electromyography (sEMG) for the vastus medialis (VM) (P = 0.02). However, caffeine had no significant effect on knee extension strength (P ≥ 0.05) or peak sEMG for the vastus lateralis (VL) (P ≥ 0.05). CONCLUSION: The results of the present study indicate that a caffeine dose of 5 mg∙kg-1 consumed 45-minutes prior to exercise is ergogenic for hand grip strength, VA and muscle activity for the VM. However, since no effect on knee extension strength and muscle activity for the VL was observed, further research into these parameters is required to understand the relationship between caffeine and muscle strength. Lastly, the present study found that genotypes in the CYP1A2 gene had no effect on caffeine response variation. However, no participants in the study were homozygous for the C allele, suggesting that future research should look to include a sample size consisting of all three genotypes.