What can isolated skeletal muscle experiments tell us about the effects of caffeine on exercise performance?

Abstract

Caffeine is an increasingly popular nutritional supplement due to the legal, significant improvements in sporting performance that it has been documented to elicit, with minimal side effects. Therefore, the effects of caffeine on human performance continue to be a popular area of research as we strive to improve our understanding of this drug and make more precise recommendations for its use in sport. Although variations in exercise intensity seems to affect its ergogenic benefits, it is largely thought that caffeine can induce significant improvements in endurance, power and strength-based activities. There are a number of limitations to testing caffeine-induced effects on human performance that can be better controlled when investigating its effects on isolated muscles under in vitro conditions. The hydrophobic nature of caffeine results in a post-digestion distribution to all tissues of the body making it difficult to accurately quantify its key mechanism of action. This review considers the contribution of evidence from isolated muscle studies to our understating of the direct effects of caffeine on muscle during human performance. The body of in vitro evidence presented suggests that caffeine can directly potentiate skeletal muscle force, work and power, which may be important contributors to the performance-enhancing effects seen in humans. Abbreviations

Caffeine enhances activity thermogenesis and energy expenditure in rats

“…Second, caffeine and vehicle did not significantly differ in their effects on interscapular brown fat temperature. The effect of caffeine on muscle work efficiency and thermogenesis seen here is consistent with the known ability of caffeine to enhance muscle power and exercise endurance . and reduce perceived exertion .…”

“…Caffeine affects not only energy balance but also exercise endurance and performance . Caffeine can increase muscle performance, energy expenditure (EE), thermogenesis, and fuel utilization through several potential mechanisms .…”

“…Lastly, caffeine activates ryanodine receptors (RYR), including RYR 1 and 3 found in skeletal muscle . Caffeine also has direct effects on skeletal muscle physiology; this could potentially occur through RYR‐induced changes in the activity of sarco/endoplasmic reticulum Ca 2+ ‐ATPase (SERCA). Changes in SERCA activity, like uncoupling induced by sarcolipin, can stimulate muscle non‐shivering thermogenesis .…”

Evaluating the effects of caffeine and sodium bicarbonate, ingested individually or in combination, and a taste-matched placebo on high-intensity cycling capacity in healthy males

“…Indeed, recent research has demonstrated that ergogenic benefit with NaHCO3 ingestion is most likely observed for TLIM at 100% WPEAK (Higgins et al 2013a). Similarly, Simmonds et al (2010) demonstrated that 5 mg.kg -1 caffeine increased TLIM at 120% V O2PEAK by ~15% although the ergogenic effects of caffeine are generally more pronounced in trained compared to non-trained individuals (Simmonds et al 2010;Tallis et al 2015).…”

“…For example, although each study adopted a dosage of 5 0.3 g.kg -1 NaHCO3, the dosage of caffeine varied between studies with Pruscino et al (2008) and Carr et al (2011) adopting ~6 mg.kg -1 whereas Kilding et al (2012) and Christensen et al (2014) adopted 3 mg.kg -1 . Additionally there were differences in approaches to abstinence of caffeine intake prior to exercise, an area recognised to limit the ability to compare studies evaluating the ergogenic effects of caffeine (Tallis et al 2015). For example, participants in Carr et al (2011) and Pruscino et al (2008) abstained for 48 hours prior to exercise whereas participants in Kilding et al (2012) abstained for the duration of the study.…”