Caffeine capsules improve muscle strength and endurance in men, review suggests
Published in the journal Nutrients and funded by the National Key R&D program of China and the Chinese Universities Scientific Fund, the research specified that benefits were observed when 6 mg/kg body weight of caffeine or more was consumed 45 minutes prior to exercise.
“An acute ingestion of caffeine capsules significantly improved muscle strength and muscle endurance in the upper body and lower body of males,” the Chinese researchers concluded, suggesting the potential for more accurate caffeine supplementation to benefit athletic performance.
Caffeine and athletic performance
Caffeine consumption for performance benefits has been a long-established practice amongst athletes, with around 73.8% of athletes reported to ingest caffeine prior to or during competition. Previous research also shows that caffeine ingestion can significantly enhance muscle strength; a parameter closely related to sporting performance. In addition, some studies have suggested an association between intakes and muscle endurance improvements.
To evaluate the effects of caffeine capsule consumption on muscle strength and endurance and resolve contradictory evidence, the researchers searched the PubMed, EBSCO, Cochrane, Web of Science, and Scopus databases to obtain relevant randomized controlled trials using key words and inclusion criteria. Data was pooled using weighted mean difference (WMD) and 95% confidence intervals.
It was determined that acute ingestion of caffeine capsules significantly improved muscle strength across professional strength trainers, amateur trainers, team sport athletes, competitive athletes, males and females. The strength benefits were observed for both upper and lower body strength.
Subgroup analysis observed that caffeine ingestion of ≥6 mg/kg BW was associated with improvements in muscle strength, while quantities less than 6 mg/kg BW were not. In addition, ingestion 45 minutes prior to exercise resulted in significant muscle strength improvements. Contrastingly, caffeine ingestion 60 minutes prior showed no significant effect.
It was revealed after further analysis that the effects on muscle strength were only significant for males, with the researchers attributing the potential lack of effect in females to the potential influence of hormonal interactions altering the metabolic rate of caffeine.
Finally, it was determined that caffeine consumption significantly improved muscle endurance within male athletes, with females again not displaying significant effects.
Caffeine interactions explained
The researchers concluded that the acute ingestion of caffeine capsules significantly improved muscle strength and endurance within the upper and lower body of males.
“The main mechanism by which caffeine enhances muscle strength is that caffeine stimulates the central nervous system and improves neuromuscular transmission by facilitating Ca2+ release from the sarcoplasmic reticulum, and inhibits Ca2+ reuptake to increase muscle contractility, ultimately leading to an increase in muscle strength," the researchers explained. "In addition, it also increases the recruitment of motor units and inhibits Ca2+ reabsorption."
They added that the mechanisms explaining the enhancement of muscle endurance through caffeine ingestion lies in its interactions with the central nervous system.
"During moderate- to high-intensity exercise, continuous muscle contractions can lead to minor damage to contractile proteins and trigger inflammation, resulting in pain," the review noted. "Caffeine ingestion helps alleviate this muscle discomfort and pain by increasing the concentration of plasma β-endorphins, thereby improving muscle endurance.
“Additionally, caffeine crosses the blood–brain barrier and binds to adenosine receptors, reducing the inhibitory effect of adenosine and subsequently enhancing muscle endurance."
Source: Nutrients
doi: 10.3390/nu16081146
“Effects of Acute Ingestion of Caffeine Capsules on Muscle Strength and Muscle Endurance: A Systematic Review and Meta-Analysis”
Authors: Weiliang Wu et al.
