Caffeine and Exercise

General Cardiovascular Effects

Caffeine and its metabolites have effects on the cardiovascular system that are thought to enhance athletic performance. Theobromine is a vasodilator that helps increase oxygen and nutrient delivery to muscle and brain tissues. Theophylline increases heart rate and heart contractility and, therefore, increases cardiac output (the amount of volume pumped by the heart per unit time). Large overdoses of caffeine can create cardiac complications, including heart palpitations and heart attack.

General Respiratory Effects

In addition to the vascular effects, caffeine also contributes to an increase in respiratory function. Theophylline acts as a smooth muscle relaxant of the bronchioles and, thus, increases lung ventilation and oxygen saturation. Caffeine is being researched as a potential drug for use in athletes with exercise-induced asthma. Caffeine is also thought to stimulate the respiratory center of the medulla and, thus, increase the ventilation rate. Caffeine can therefore increase respiratory readiness and prepare the body for athletic activity by increasing overall blood oxygen concentrations.

Dehydration and Renal Effects

One of the common worries about the consumption of caffeine is dehydration. While caffeine has shown mild diuretic (water excretion) effects on the kidney, consuming caffeinated beverages does not show a significant increase in overall fluid loss in a 24-hour period. Therefore, athletes should not increase their fluid intake when using moderate amounts of caffeine (<456 mg). However, when large ergogenic doses are taken, the risk of fluid loss is higher, and more water should be consumed to prevent hypovolemia (a drop in blood pressure). Regardless of caffeine intake, athletes should always monitor fluid intake during heavy training regimens.

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