Collapse After Exercise
At the end of a marathon, a runner sprints over the finish
line, falls down and lies unconscious for a short time. What's the
most likely cause? The possibilities include dehydration,
hyponatremia (excessive fluid intake with too little salt in the
blood), heat stroke, drunkenness, a heart attack or stroke.
Usually it is none of these. Almost all athletes who collapse after
finishing a marathon suffer from postural hypotension: lack of
blood flow to the brain because blood drops from the brain to the
legs. Treatment is to lie the person on his back, raise his feet high
over his head and wait for him to revive. If he or she is not alert
within seconds, you should consider the more serious causes of
unconsciousness and get medical help immediately.
When you run, your heart pumps blood through your
body, but it gets lots of help from your legs. When your leg
muscles contract, they squeeze veins near them to push blood
toward your heart. When your leg muscles relax, the veins near
them fill with blood. This alternate contracting and relaxing of your
leg muscles serves as a second heart. When you sprint toward
the finish line, your leg muscles increase their pumping of blood. If
you stop suddenly, the leg muscles top pumping and blood pools
in your legs, your brain doesn't get enough oxygen, and you pass out.
This is the reason you should always cool down after
vigorous exercise. If you slow down gradually, your leg muscles
stop pumping gradually and you heart has time to pick up its
share of the workload. Many people believe that cooling down
helps to prevent muscle soreness by clearing lactic acid from
muscles, but there is no evidence to support this theory. Muscle
soreness after exercise is caused by small tears in the muscle
fibers, not by accumulated lactic acid. Plan to cool down just to
prevent dizziness or fainting.
January 15, 2007
Checked 8/8/10