Muscle caffeine effects

Although research has been suggestive of caffeine modulated increases in muscular contractions leading to hand tremor, it is more likely that the hand tremor response is the result of caffeine s effects on the central nervous system.32 There is even evidence that moderate doses of caffeine may actually diminish muscle tone.32... 

The methylxanthines have effects on the central nervous system, kidney, and cardiac and skeletal muscle as well as smooth muscle. Of the three agents, theophylline is most selective in its smooth muscle effects, whereas caffeine has the most marked central nervous system effects. 

A much milder and legal stimulant is caffeine, depicted in Figure 14.27. A number of mechanisms have been proposed for caffeines stimulatory effects. Perhaps the most straightforward mechanism is caffeine s facilitating of the release of norepinephrine into synaptic clefts. Caffeine also exerts many other effects on the body, such as dilation of arteries, relaxation of bronchial and gastrointestinal muscles, diuretic action on the kidneys, and stimulation of stomach-acid secretion. 

Breathing rate increases in response to caffeine. The effect on respiration occurs at the level of the brain stem s respiration control center. Theophylline has the most potent action of all the methylxanthines, affecting the smooth muscle of the bronchial tree in the lungs. This is why theophylline is a treatment for asthma. Doctors may recommend weak tea for their asthmatic patients with colds this bronchodilating action of the theophylline in the tea will aid in clearing mucus. 

Caffeine s primary action is stimulation of CNS activity but, as we saw, caffeine is distributed freely throughout the body. Such distribution is evidenced by caffeine s actions outside the CNS contraction of striated muscle, including the heart relaxation of smooth muscle, especially the coronary arteries, uterus, and bronchi diuretic effects on the kidneys at higher doses, a stimulating effect on respiration elevation of basal metabolism and various endocrine and enzymatic effects (Levenson Bick, 1977 Rail, 1990a). Caffeine s effects on the body s systems provide good evidence for the blockade of adenosine receptors as its mechanism of action because caffeine s effects essentially arc opposite to those of adenosine (Leonard et al., 1987). 

Caffeine has been shown to have a bronchial and smooth muscle relaxant effect and to improve skeletal muscle contractility. Significant increases in hand tremor and forearm extensor electromyogram were observed in human subjects after the ingestion of 6mgkg of caffeine. This effect is more likely due to a CNS stimulatory effect than to direct action on the muscle fibers. Skeletal muscle fatigue can be reversed by high concentrations of caffeine obtained only in vitro but not in vivo. 

Caffeine is a strong activator of CICR it sensitizes RyR to activating Ca2+ and increases the maximum attainable level. Because high concentrations (>mM) of caffeine effectively discharge Ca2+ from the Ca2+ store, it is frequently used for experimental evaluation of functional occurrence of RyRs. Caffeine is used for diagnosis of MH muscles biopsied from MH patients contract by a lower dose of caffeine than normal human, due to an enhanced CICR activity (see Disease)./Para>... 

Caffeine is a mild to potent CNS stimulant, with the degree of its stimulating effect dependent on the dose administered. Caffeine stimulates the CNS at all levels, including the cerebral cortex, die medulla, and the spinal cord. Caffeine has mild analeptic (respiratory stimulating) activity. Other actions include cardiac stimulation (which may produce tachycardia), dilatation of coronary and peripheral blood vessels, constriction of cerebral blood vessels, and skeletal muscle stimulation. Caffeine also has mild diuretic activity. 

For over three decades, laboratory research has shown caffeine to be effective at mobilizing calcium in skeletal muscle. In vitro experiments have amply demonstrated that caffeine lowers the excitability threshold and extends the length of muscular contractions via calcium release from the sarcoplasmic reticulum.1012 Caffeine also inhibits calcium reuptake by the sarcoplasmic reticulum, perpetuating calcium availability for muscle work.1318 Also, caffeine promotes increased twitch tension development in muscles.1718... 

Such results suggest a need for further research comparing trained with untrained subjects, along with an examination of muscle fiber type ratios of experimental subjects. Also, the question of subjects habituation to caffeine needs to be explored more fully. For the present, the reported ergogenic effects of caffeine on muscular strength must be viewed with skepticism and perhaps be attributed to the psychostimulant properties of caffeine. 

Perhaps the most intriguing perspective is that caffeine s major effects have little to do with muscles and fat metabolism but result from its psychostimulant effects, enhancing mood, improving attitude towards exercise, and thus motivating athletes to work harder and longer. This would account for its purported inability to alter strength, which may be a less psychologically malleable variable, while endurance performance is sometimes believed to be more amenable to force of will. 

Wendt, I. and Stephenson, D., Effects of caffeine on calcium-activated force production in skinned cardiac and skeletal muscle fibers of the rat, European Journal of Physiology, 398, 210, 1983. 

Lopes, J. M., Aubier, M., Jardin, J., Aranda, J. V., and Macklem, P. T., Effects of caffeine on skeletal muscle function before and after fatigue, Journal of Applied Physiology, 54, 1303, 1983. 

Bugyi, G. J., The effects of moderate doses of caffeine on fatigue parameters of the forearm flexor muscles, American Corrective Therapy Journal, 34, 49, 1980. 

Essig, D., Costill, D. L., and Van Handel, P. J., Effects of caffeine ingestion on utilization of muscle glycogen and lipid during leg ergometer cycling, International Journal of Sports Medicine, 1, 86, 1980. 

Dreja K, Nordstrom I, Hellstrand P 2001 Rat arterial smooth muscle devoid of ryanodine receptor function effects on cellular Ca2+ handling. Br J Pharmacol 132 1957-1966 Martin C, Hyvelin JM, Chapman KE, Marthan R, Ashley RH, Savineau JP 1999 Pregnant rat myometrial cells show heterogeneous ryanodine- and caffeine-sensitive calcium stores. Am J Physiol 277 C243-C252... 

Caffeine is a powerful stimulant of central nervous system and also stimulates the cardiac muscle. However, high amounts of the alkaloid have noticeable irritation of gastrointestinal tract as well causes matw unwanted effects [1]. 

Caffeine increases the capacity of skeletal muscle. This effect is probably due to the release of intracellular Ca2+, and is observable in human performance. The contribution of central effects is also likely. Whether caffeine actually benefits exercise is contested (Spriet 1995 Dodd et al. 1993). Research does not consistently support caffeine enhancement of performance during high-intensity, short-term exercise. There is some evidence to suggest benefit during prolonged, moderate-intensity exercise. 

These compounds competitively inhibit phosphodiesterase, resulting in an increase in cyclic AMP (see Box 14.3) and subsequent release of adrenaline. This leads to the major effects a stimulation of the central nervous system (CNS), a relaxation of bronchial smooth muscle, and induction of diuresis. These effects vary in the three compounds. Caffeine is the best CNS stimulant, and has weak diuretic action. Theobromine has little stimulant action, but has more diuretic activity and also muscle relaxant properties. Theophylline also has low stimulant action and is an effective diuretic, but it relaxes smooth muscle better than caffeine or theobromine. 

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