DEAR DR. DONOHUE: I assist the baseball coach at our local high school. I graduated from college with a degree in physiology, and I have always been interested in applying physiology to sports performance. I am particularly interested in hand-eye coordination. I know it’s especially important in hitting a baseball. The coach is interested in my applying any techniques I know to improve the team’s batting averages. Will you make any comments on this? — P.F.

ANSWER: Hand-eye coordination involves the arms and hands quickly and accurately reacting to signals sent to the brain by the eyes. At the high-school level, the pitched ball isn’t traveling at 90-miles-per-hour speeds, but it is traveling fast enough to make hitting the ball a challenge. Training that improves a person’s arm and hand reaction to visual signals does raise batting averages. It’s also an important skill in fielding a ball.

If you can get a copy of the March 2011 issue of Training and Conditioning, you’ll find an article written by Michael Zupan, who is in charge of the United States Air Force Academy’s Human Performance Laboratory. It’s devoted to this topic.

One of Dr. Zupan’s hand-eye training techniques goes like this: Two large charts with letters on them are fixed to a wall and placed 10 feet apart. A baseball batter stands 8 feet away from the wall in the same kind of stance he or she assumes when batting. He is exactly between the two charts. The drill is to have the batter quickly call out the first letter on the chart on his left side and then quickly call out the first letter on the chart on his right side. The entire sequence of letters is called out. No head movement is allowed. Only the eyes move from one chart to the other.

This sort of training has been shown to increase batting averages by refining the athlete’s hand-eye coordination.

DEAR DR. DONOHUE: You are familiar with energy drinks, aren’t you? Well, my teenage son has gotten in the habit of drinking them far too often. He says they really do increase his energy. I’m worried that they might be dangerous. Will you please provide some information? — B.B.

ANSWER: One kind of energy drink is a mixture of caffeine and alcohol. In November 2010, the U.S. Food and Drug Administration declared such combinations to be unsafe. I’m sure your son isn’t using this sort of energy drink. Others are.

Your boy is likely drinking caffeinated beverages. The amount of caffeine in these drinks ranges from 50 to 505 mg of caffeine per can. A 6-ounce cup of coffee contains 77 to 150 mg of caffeine.

Adolescents drinking such large amounts of caffeine can suffer sleep disturbance, shaking hands and possibly a rise in blood pressure. One school district has banned these drinks at all practices and games. I think that’s a good policy.

DEAR DR. DONOHUE: According to my coach, I have a groin injury. Just what does that mean, and how long does it take to heal? — G.M.

ANSWER: The “groin” means different things to different people. It should not mean the genital organs. It’s the junction of the thigh with the abdomen — the inner aspect of that junction.

Groin muscles draw the legs toward each other. A groin strain or pull indicates that some muscle fibers have been torn. Usually, that’s the result of fast, twisting motions.

It can take a full month to recuperate from a groin pull. If your pain isn’t lessening in one week, see the family doctor. You want to make sure the coach’s diagnosis is correct.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from