Does caffeine alter muscle carbohydrate and fat metabolism during exercise?

Human Health and Nutritional Sciences, University of Guelph, Guelph, ON N1G2W1, Canada.
Applied Physiology Nutrition and Metabolism (Impact Factor: 2.34). 12/2008; 33(6):1311-8. DOI: 10.1139/H08-129
Source: PubMed


Caffeine, an adenosine receptor antagonist, has been studied for decades as a putative ergogenic aid. In the past 2 decades, the information has overwhelmingly demonstrated that it indeed is a powerful ergogenic aid, and frequently theories have been proposed that this is due to alterations in fat and carbohydrate metabolism. While caffeine certainly mobilizes fatty acids from adipose tissue, rarely have measures of the respiratory exchange ratio indicated an increase in fat oxidation. However, this is a difficult measure to perform accurately during exercise, and small changes could be physiologically important. The few studies examining human muscle metabolism directly have also supported the fact that there is no change in fat or carbohydrate metabolism, but these usually have had a small sample size. We combined the data from muscle biopsy analyses of several similar studies to generate a sample size of 16-44, depending on the measure. We examined muscle glycogen, citrate, acetyl-CoA, glucose-6-phosphate, and cyclic adenosine monophosphate (cAMP) in resting samples and in those obtained after 10-15 min of exercise at 70%-85% maximal oxygen consumption. Exercise decreased (p < 0.05) glycogen and increased (p < 0.05) citrate, acetyl-CoA, and glucose-6-phosphate. The only effects of caffeine were to increase (p < 0.05) citrate in resting muscle and cAMP in exercise. There is very little evidence to support the hypothesis that caffeine has ergogenic effects as a result of enhanced fat oxidation. Individuals may, however, respond differently to the effects of caffeine, and there is growing evidence that this could be explained by common genetic variations.

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    • "The discussed mechanisms for caffeine's ergogenic effect on endurance performance include the enhancement of fat oxidation that has been assumed to preserve muscle glycogen stores. However, a study by Graham et al. (2008) has revealed that the ergogenic effect of caffeine on endurance exercise is not a result of enhanced fat oxidation. An alternative explanation is that caffeine reduces discomfort or pain during exercise and enables the subjects to exercise at higher intensities and/or for a longer time (Motl et al., 2003). "
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    ABSTRACT: The aim of this study was to compare the neuromuscular function of the plantar flexors following caffeine or placebo administration. Thirteen subjects (25 ± 3 years) ingested caffeine or placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after caffeine or placebo intake. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque, and neural drive to the muscles were measured. Triceps surae muscle activation was assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100 ms, 100–200 ms) and maximal voluntary contraction (MVC). Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during MVC, V-wave) and peak twitch torques were evaluated. The isometric maximum voluntary torque and evoked potentials were not different. However, we found a significant difference between groups for rate of torque development in the time intervals 0–100 ms [41.1 N·m/s (95% CI: 8.3–73.9 N·m/s, P = 0.016)] and 100–200 ms [32.8 N·m/s (95% CI: 2.8–62.8 N·m/s, P = 0.034)]. These changes were accompanied by enhanced neural drive to the plantar flexors. Data suggest that caffeine solely increased explosive voluntary strength of the triceps surae because of enhanced neural activation at the onset of contraction whereas MVC strength was not affected.
    Scandinavian Journal of Medicine and Science in Sports 02/2015; 25(1). DOI:10.1111/sms.12243 · 2.90 Impact Factor
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    • "Caffeine induces numerous physiological effects. Although its stimulating effects on exercise performance in humans were initially thought to occur via increased fatty acid oxidation rates and muscle glycogen-sparing effect [5] [7], several studies reported conflicting findings [12] [13]. In addition to peripheral actions, caffeine was shown to reduce perception of effort during exercise, suggesting that some ergogenic effects may be partially accounted for by caffeinemediated maintenance of central nervous system (CNS) drive [14]. "
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    ABSTRACT: Aims. To evaluate the possible additive effects of beetroot juice plus caffeine on exercise performance. Methods. In a randomized, double-blinded study design, fourteen healthy well-trained men aged 22 ± 3 years performed four trials on different occasions following preexercise ingestion of placebo (PLA), PLA plus 5 mg/kg caffeine (PLA+C), beetroot juice providing 8 mmol of nitrate (BR), and beetroot juice plus caffeine (BR+C). Participants cycled at 60% maximal oxygen uptake ([Formula: see text]max) for 30 min followed by a time to exhaustion (TTE) trial at 80% [Formula: see text]max. Saliva was collected before supplement ingestion, before exercise, and after the TTE trial for salivary nitrate, nitrite, and cortisol analysis. Results. In beetroot trials, saliva nitrate and nitrite increased >10-fold before exercise compared with preingestion (P ≤ 0.002). TTE in BR+C was 46% higher than in PLA (P = 0.096) and 18% and 27% nonsignificant TTE improvements were observed on BR+C compared with BR and PLA+C alone, respectively. Lower ratings of perceived exertion during TTE were found during 80% [Formula: see text]max on BR+C compared with PLA and PLA+C (P < 0.05 for both). Conclusions. Acute preexercise beetroot juice coingestion with caffeine likely has additive effects on exercise performance compared with either beetroot or caffeine alone.
    12/2013; 2013(3):396581. DOI:10.5402/2013/396581
    • "As a result, there may be less accumulation of glucose in the blood after consuming green coffee bean extract with dextrose compared with consuming caffeine with dextrose. The effect of pre-exercise caffeine consumption on glucose metabolism during exercise has been reviewed [5]. The effect of pre-and during-exercise [16], as well as post-exercise [7] [8] [17] [18] caffeine supplementation on glucose metabolism and homeostasis during an acute, passive recovery has been investigated. "

    Journal of the International Society of Sports Nutrition 12/2013; 10(Suppl 1):P2-P2. DOI:10.1186/1550-2783-10-S1-P2 · 1.91 Impact Factor
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