DEAR DR. DONOHUE: I coach a high-school football team on a voluntary basis. I live in a small town, and the high school is small. I am not a trained coach, but I have had this coaching job for 15 years. We are going to start practice in a short time. I need some guidance on how to protect these kids from heat stroke. I learned of a heat-stroke death in a high-school player, and I don’t want that on my conscience. – B.R.

ANSWER: It takes the body 10 to 14 days to acclimatize to working out in the heat. Acclimatization is complete when the body sweats sooner, loses less salt in the sweat and increases its blood flow to the skin to dissipate body heat.

Therefore, in the first days of practice, your players should wear only shorts, shirts and helmet. Schedule practice for early mornings or evenings. Provide the boys with free access to water. If they are sweating a great deal, add some salt to the water (one-eighth teaspoon to a quart) or give them sports drinks.

Even when the temperature is only 85 F (29 C), the conditions can become dangerous if the humidity hovers near 100 percent. When the temperature is 90 F (32.2 C) and the humidity is 70 percent, reduce practice time. At a temperature of 95 (C) and humidity of 80 percent, call it off.

Heat stroke is an emergency. Signs that an athlete is suffering from it include mental slowdown. The player appears dazed. Heart and breathing rates speed up. Body temperature rises to 104 F (40 C). Cool a player who demonstrates these signs by sponging him with cool water and turning a fan on him. Get him to an emergency facility quickly.

DEAR DR. DONOHUE: Will you answer a few sunglasses questions for me? I used to pick them to make a fashion statement, but I have heard that the wrong kind can cause eye problems. Are dark lenses the best? What color? Do children need to wear them? – L.A.

ANSWER: The most important function of good sunglasses is filtering ultraviolet light. UV light can lead to cataract formation and can damage the most sensitive part of the retina, the macula. These changes occur later in life, but much can be done to prevent them if you are UV-light-protected from an early age.

Read the label on the glasses. You want a pair that filters out ultraviolet rays, both ultraviolet A and B. On some glasses, the label is marked “Z 80.3.” That indicates that the glasses meet the criteria of the American National Standards Institute and block 60 percent of ultraviolet A rays and 95 percent of ultraviolet B.

Glasses that carry a sticker marked AOA (American Optometry Association) block 99 percent of ultraviolet rays.

The darkness of the lens has little bearing on its protection. Dark lenses that don’t filter UV light might be more dangerous than not wearing glasses. The dark lens makes the pupil dilate, and more UV rays can enter the eye.

As for the shade of the lens, gray, brown and green lenses distort ambient color the least.

Yes, children should wear sunglasses that filter ultraviolet light.

DEAR DR. DONOHUE: I have entered a 10K (6-mile) race that’s being held in August. I know I should drink lots of water before and during the race, but how much is “lots of”? – N.K.

ANSWER: Now, while you practice running, weigh yourself before the run and after. Every pound of weight lost represents the loss of a pint (500 ml) of body fluid. That gives you a gauge of how much water you need to keep your body hydrated.

If a run lasts more than an hour, include some salt in your replacement fluid. Either drink a sports drink or carry a small container of salt with you and take a pinch of it with every drink of water.

Prolonged runs during which a runner drinks only water can lead to hyponatremia (HI-poe-nuh-TREE-me-uh) – low body salt. People have died from it. Ran on 6-30th.

DEAR DR. DONOHUE: The middle finger on my right hand sticks. I mean, I bend it, and at about mid-bend position, it locks. I work on it for a while, it pops, and I can bend it fully and straighten it normally.

I try to use my left hand as often as I can. The sticking and popping in my right hand hurts. What is going on? – C.H.

ANSWER: Your description fits the bill for trigger finger.

Tendons that bend and straighten the fingers come from forearm muscles. In the palm, the tendons are surrounded by protective sheaths of tissue. When a sheath becomes inflamed, it holds on to the tendon so the finger stops in mid-bend.

With a little patience and manipulation, the tendon breaks free and makes a popping noise that sounds like cocking a gun’s trigger.

If a trigger finger is treated soon after it develops, a splint might be all that is needed to rid the tendon sheath of the inflammation. A cortisone injection often works if the splint treatment fails. In cases when all conservative treatments meet with no success, surgery can come to the rescue.

DEAR DR. DONOHUE: I have been working on my tan for two weeks. White circles have appeared on my back and neck. Is this sun poisoning? – R.T.

ANSWER: It’s not sun poisoning. It is a fungal skin infection called tinea versicolor.

Areas of skin invaded by the fungus lose their color. Adjacent tanned skin makes those patches more noticeable.

A 2.5 percent selenium sulfide shampoo is an inexpensive and fairly reliable treatment. You lather the skin with the shampoo and a small amount of water and let the lather stay on the skin for 10 minutes. Then rinse the entire body. It takes a full week of daily applications to get rid of the fungus.

If selenium sulfide falls on its face, antifungal creams, lotions or sprays are your next move. Your doctor might have to step in for prescription items.

It can take a full year for the color to return.

How does one “work on a tan”? You would be doing your skin a huge favor by staying out of sunlight.

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.