The study was funded by the Central China Normal University and the National Natural Science Foundation of China.
Researchers found that coffee boosted exercise performance and post-exercise recovery of active individuals in an RCT, but not anaerobic performance, which refers to muscles efficiency in utilising oxygen.
“Coffee ingestion with high caffeine level (6mg/kg body weight) significantly enhanced skeletal muscle reactivity at rest. However, the improvement of exercise performance with coffee intake is not accompanied by alterations in muscle oxygen extraction,” wrote researchers in Journal of the International Society of Sports Nutrition.
The effects of coffee ingestion on skeletal muscle microvascular function, or how caffeine levels affect muscular blood vessels, are not well understood.
Researchers therefore designed a study to explore the effects of coffee ingestion on blood flow while at rest and how effectively muscles use oxygen during intense exercise, specifically in physically active individuals.
Caffeine effects on muscle recovery and performance
This study used a single-group, repeated measures design, where all participants went through the same experiment three times under different conditions.
Twenty healthy young male participants with an average age of 20 were recruited for this study. All participants were physically active and do not have caffeine consumption habit.
They abstained from alcohol, caffeine, and hard exercise for 24 hours before each session.
Each session is 48 hours apart, where participants consumed coffee that contained different levels of caffeine each time.
Participants consumed coffee with low caffeine, high caffeine, and a placebo at each different session in a randomised order.
Nescafé Original coffee powder with 3.4g caffeine/100g was used for the low caffeine servings, which had a dosage of 3 mg/kg body weight.
The high caffeine servings used the same coffee powder and had a dosage of 6 mg/kg body weight.
Nescafé Decaf powder with very little caffeine was used to prepare the placebo.
The coffees were served by mixing coffee powder with 300ml warm water.
Before consuming the coffee, participants laid down to rest for at least 10 minutes, and baseline skeletal muscle reactivity at rest was measured using near-infrared spectroscopy (NIRS).
They then consumed a cup of coffee that had to be finished within five minutes.
Participants then laid down to rest for 45 minutes.
Skeletal microvascular reactivity at rest and oxygen extraction during exercise was assessed using NIRS, which monitors oxygen levels.
VO2peak and Wpeak, which measured peak oxygen consumption and peak power output respectively, were also assessed.
Potential of coffee as a valuable supplement for athletes
Post coffee consumption, the mean tissue saturation index 10s slope (TSI10) – which measures the ability to take up oxygen again after a temporary stop in blood supply – was significantly higher for low caffeine consumption at around 1.7%s-1 compared to the placebo at around 1.55%s-1.
However, no significant differences in TSI10 were detected between low caffeine and high caffeine conditions.
Researchers also measured TSI half time recovery (TSI ½), which looks at how long it takes for oxygen levels to return halfway back to normal after blood flow has been restricted and then restored.
The high caffeine condition showed significant less TSI ½ at a mean of around eight seconds compared to the placebo, which showed a mean of around 10 seconds.
However, no discernible difference was observed among the three conditions – low caffeine, high caffeine, and placebo – for microvascular oxygen extraction during exercise. This is despite the greater Wpeak found for the high caffeine condition at 275.1 ± 46.1 W compared to placebo at 246.7 ± 40.3 W.
This finding contrasts with previous research, which has shown that caffeine can enhance performance, particularly in endurance and high-intensity exercises.
Researchers attributed the improvement in maximum aerobic power to two other factors: better muscle contraction and a reduced feeling of effort during exercise. These are likely due to caffeine’s ability to enhance muscle contraction through increased calcium release and reduce the perception of effort by stimulating the nervous system.
“The primary finding was that coffee intake with high level of caffeine (6 mg/kg body weight) resulted in a significant enhancement in muscle microvascular reactivity at rest, which highlights the potential of caffeine as a potent modulator of vascular response,” said researchers.
The finding of improvement in skeletal muscle reactivity at rest after high caffeine intake coincides with previous studies which indicate that skin microvascular function is elevated with acute coffee intake.
This finding is crucial, as it is well established that the microvascular network plays a pivotal role in physical exertion and post-exercise recovery, said researchers.
The mechanisms through which coffee affects skeletal muscle microvascular function is complicated, but caffeine is probably the main factor that boosts performance. The main reason may be its effect on the endothelium – cells lining the blood vessels.
Research shows that caffeine can increase the release of nitric oxide, which helps relax and widen blood vessels, improving blood flow.
Therefore, researchers believe this study provides evidence that the acute intake of coffee could significantly enhance skeletal muscle microvascular reactivity at rest and improve exercise capacity.
“Findings of this study highlighted the ergogenic role of coffee, and support the use of coffee as a valuable supplement for exercise performance and post-exercise recovery. While not directly investigated in the current study, the vascular effect observed here could suggest a potential dietary therapeutic effect for coffee in people with compromised vascular function, although clearly more research is needed to confirm this notion.
“Further, the findings regarding Wpeak were similar to previous studies and suggest the role of caffeine as a modulator for endurance sports where circulation and oxygen utilisation are crucial,” concluded the researchers.
Source: Journal of the International Society of Sports Nutrition
DOI: https://doi.org/10.1080/15502783.2024.2409673
“Effects of coffee intake on skeletal muscle microvascular reactivity at rest and oxygen extraction during exercise: a randomized cross-over trial”
Authors: Bin Leng, Haizhen Huang et al.
