By Eric Heiden M.D.
Tribune Media Services
More and more kids are being diagnosed with what was once thought to be an almost exclusively adult malady: high blood pressure. These children join the large contingent of American adults -- estimated to be 25 percent of the population -- who also have high blood pressure. New research shows that exercise lowers blood pressure in children as effectively as it does in adults.
Numerous adult studies have demonstrated that exercise offers a drug-free alternative for significantly lowering blood pressure. But this new study, published in the October issue of the Journal of Human Hypertension, shows that structured physical training activity two or more times a week has a beneficial effect on blood pressure in children 11 to 18.
Blood pressure is the force of your blood pushing against the walls of your arteries. According to the National Heart, Lung, and Blood Institute, blood pressure that is 120/80 or lower is normal; blood pressure that is 140/90 or higher is high. You can have high blood pressure for many years without knowing it, and during that time it can damage your heart, brain, eyes and kidneys.
Exercise lowers blood pressure several ways. When you exercise, your capillary network, which carries oxygen to your muscles, expands. A capillary is the smallest, most distant part of your arterial system. If your arteries are freeways, your capillaries are the driveways. That's where oxygen is handed over to your cells and carbon dioxide is swept away. Exercise adds virtually miles of capillaries. An average person has one capillary for every five to 15 muscle fibers. Top endurance athletes have one capillary for every single muscle fiber.
Any fluid in a hydraulic system moves from a point of higher pressure to a point of lower pressure. To push your blood, your heart has to produce enough pressure to offset the lower pressure downstream in your capillaries. If pressure rises downstream in your capillaries, your upstream blood pressure has to climb as well, to allow the whole system to function. When the pressure downstream eases, so can your upstream blood pressure.
The thinning of blood that comes with exercise also lowers blood pressure. When you participate in regular exercise, you produce more red blood cells and more plasma, the liquid that holds the cells in suspension. Exercise triggers an increase in both red blood cells and plasma, but the amount of plasma increases by a greater proportion, which thins your blood. Thinner blood is easier to push through the capillaries, which are very, very small (about one blood cell wide). Imagine the ease with which you can draw water up a straw. Moving a thick milk shake up the same straw requires more work. Likewise, thinner blood is much easier for your heart to move than thicker blood, and thinner blood means oxygen reaches farther out into your capillaries with less effort.
Exercise also eliminates plaques that build up normally in aging arteries. The lower pressure inside of your arteries that comes with exercise also makes them more elastic, much like a garden hose that is rigid with high-pressure water flowing through it becomes more flexible when you turn down the water pressure.
Eric Heiden, M.D., a five-time Olympic gold medalist speed skater, is an orthopedic surgeon in Utah. He co-authored "Faster, Better, Stronger: Your Fitness Bible" (HarperCollins) with Max Testa, M.D., and DeAnne Musolf. Visit www.fasterbetterstronger.com.