The human knee is not a very stable joint. It's simply two big, long bones held together by ligaments. Not surprisingly, it's very vulnerable to injury. Players involved in contact sports -- such as football, hockey, basketball and soccer -- are especially likely to suffer from knee injuries.
Over the years, many outstanding football players have had their careers cut short by a knee injury. Superstars like Joe Namath, Gale Sayers, Dick Butkus and Larry Brown come immediately to mind. Bobby Orr, one of hockey's greatest, was forced into retirement after undergoing many knee operations.
There are at least five tissues in the knee that can be injured during athletic activity: the cartilage, the ligaments, the muscles surrounding the knees, the kneecap (the bone in front of the joint) and the kneecap tendons. No wonder knee injuries are so common! Almost any wrong twist or turn can lead to pain and injury.
But there are several ways to protect your knees from injury during contact sports:
*Don't wear cleats. They anchor your foot to the ground. Many pro teams now outfit their athletes in cleatless shoes.
*Run with short, choppy steps. The less time your foot is in contact with the ground, the less chance there is of knee injury. If you know you're going to be hit, shorten your stride.
*If possible, protect your knees from a direct hit, especially from the side or back. That's where the knee is most susceptible and one reason why the National Football League has banned crack-back blocks.
*Exercise the muscles around the knee to make the muscles and ligaments stronger and more resistant to injury.
Q: I'd like to learn to play tennis, but I'm really uncoordinated. How can I improve my coordination?
A: Coordination is a complex process, partly inherited and partly cultivated. Although you can't choose your parents, you can still improve your coordination.
Coordination begins with your eyes. The eyes transmit the images you see along nerves to the brain. The brain interprets the signals, determines which of your 500 muscles should contract and how hard and how fast the contractions should be. Then, the brain sends the message along another set of nerves to control the appropriate muscles.
For each muscle that contracts, there is an opposing muscle that relaxes. The brain coordinates these movements simultaneously. The whole, miraculous process takes only a fraction of a second.
When you hit a tennis ball with your racket, every one of your muscles receives instructions from your brain. That's why you can spend an entire lifetime perfecting your coordination.
The best way to improve coordination for any sport is to practice that sport. Repeatedly practicing the same movements will help your brain interpret messages faster. It also helps your brain send more specific messages to your muscles so that the motion is more precise and more efficient.
So, to rocket a volley into just the right spot on the other side of the net, practice the move repeatedly, teaching your brain to coordinate the appropriate muscles precisely.
Q: I know you're supposed to drink a lot of water when you exercise, but sometimes it gives me a headache. Why?
A: You may be one of a small number of individuals who is unusually susceptible to water intoxication.
Here is what happens:
nTC You normally have the same concentrations of minerals inside and outside the cells in your body. When you drink large amounts of water, which contain few minerals, the concentration of minerals outside the cells is diluted, compared to the concentration inside the cells. This causes water to move into the cells so they swell. Swollen brain cells will cause headache and, sometimes, even convulsions.
Never drink more than a couple of glasses of water without also eating something. The food will provide enough minerals to protect your brain cells from swelling.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition