Caffeine is OK before exercise for young people, or conditioned older exercisers without the risk factors of heart disease. But those who don't fall in these two categories might want to think twice
about that cup of joe before working out:
In healthy volunteers, the equivalent of two cups of coffee reduced the body's ability to boost blood flow to the heart muscle in response to exercise, and the effect was stronger when the participants were in a chamber simulating high altitude, according to a new study in the Jan. 17, 2006, issue of the Journal of the American College of Cardiology.
Blood flow normally increases in response to exercise, and the results indicate that caffeine reduces the body's ability to boost blood flow to the muscle of the heart on demand. The ratio of exercise blood flow to resting blood flow, called the myocardial flow reserve, was 22 percent lower in the group at normal air pressure after ingesting caffeine and 39 percent lower in the group in the high-altitude chamber. Dr. Kaufmann said that caffeine may block certain receptors in the walls of blood vessels, interfering with the normal process by which adenosine signals blood vessels to dilate in response to the demands of physical activity.
"Although these findings seem not to have a clinical importance in healthy volunteers, they may raise safety questions in patients with reduced coronary flow reserve, as seen in coronary artery disease, particularly before physical exercise and at high-altitude exposure," the researchers wrote.
I've found the less in my stomach before a workout, the better. I try to avoid eating or drinking anything for at least an hour before a workout. But that's just me