Caffeine and Exercise: Metabolism and Performance

School of Human Biology, University of Guelph, Ontario.
Canadian journal of applied physiology = Revue canadienne de physiologie appliquée (Impact Factor: 1.3). 07/1994; 19(2):111-38. DOI: 10.1139/h94-010
Source: PubMed


Caffeine ingestion prior to prolonged exercise delays fatigue. However, the mechanisms involved are very unclear. Caffeine is associated with elevated plasma epinephrine but the metabolic impact of this is uncertain. Glycogen sparing occurs in active muscle, at least in the first few minutes, but studies have generally failed to demonstrate enhanced fat metabolism. The demethylation of caffeine by the hepatic cytochrome P-450 oxygenases begins within minutes and dimethylxanthines (especially paraxanthine) are generated. These compounds appear in the plasma within an hour of caffeine ingestion and may have effects on tissues that have been attributed to caffeine and/or epinephrine. While the most widely supported theory is that caffeine and other methylxanthines are adenosine receptor antagonists, this action alone cannot explain all of the observed responses. Nevertheless, habituation to and withdrawal from caffeine are associated with up and down regulation of adenosine receptors. One study demonstrated marked differences in the effects of caffeine on the plasma concentrations of epinephrine and dimethylxanthines between caffeine users and nonusers. Caffeine is clearly a very active drug that has many effects on humans including increasing exercise endurance. This can be associated with muscle glycogen sparing and elevated plasma epinephrine, but the underlying mechanisms are unknown.

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Available from: Terry Graham, Jun 16, 2014
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    • "If confirmed, the theory of striated urethral and/or pelvic muscular fatigue in SUI may lead to a reconsideration of the conservative management of SUI, especially for programs of pelvic floor electrostimulation, since nutritional status, musculature fiber type, and stimulation frequency directly affect muscular fatigue. Moreover, the use of drugs such as caffeine that limit neuromuscular fatigue [16] should be discussed. "
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    ABSTRACT: The physiology of urinary continence during stress is complex and the role of passive and active mechanisms remains unclear. Coughing leads to a contraction of urethral rhabdomyosphincter and pelvic floor muscles leading to a positive urethro-vesical gradient and continence. Neuromuscular fatigue can involve all striated muscles, including rhabdomyosphincter, peri-urethral and pelvic floor muscles. This article reviews results of studies assessing perineal muscular fatigue in urinary incontinence. A systematic review of the literature (Medline, Pascal and Embase) with use of the MESH keywords fatigue, stress, urinary incontinence, pelvic floor, urethra, urethral pressure, and muscle. Animal models have shown that the pelvic muscles (iliococcygeus and pubococcygeous) exhibit more neuromuscular fatigue than classical skeletal striated muscles (i.e. soleus muscle). Although the human external urethral sphincter is considered to be a highly fatigue-resistant muscle with its high proportion of slow muscle fibers, repeated coughing seems to lead to decreased urethral pressure in numerous women affected with stress urinary incontinence. In this case, "urethral fatigue" might be a possibility. Although few studies have focused on perineal muscular fatigue, such increased fatigue in pelvic floor muscles may play a role in the pathophysiologic features of stress urinary incontinence in women.
    Annales de Réadaptation et de Médecine Physique 08/2006; 49(6):331-6, 413-7. DOI:10.1016/j.annrmp.2006.03.010
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    • "Effects of caffeine on performance. There are several recent and comprehensive reviews of the effects of caffeine on exercise performance and a detailed review of the literature will not be attempted here (Dodd et al. 1993; Graham et al. 1994; Spriet, 1997). There are a number of studies showing bene®cial effects of caffeine ingestion on a variety of laboratory tests of endurance performance. "
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