DEAR DR. DONOHUE: I was putting a hot pack on my sore arm, and my wife saw me. She said I should use a cold pack. When do you use the hot pack, and when do you use the cold pack? – E.W.

ANSWER: For a just-happened injury, cold is better. Cold packs are good; ice is even better. A simple way to make an ice pack is to freeze water in a paper cup. When you take it out of the freezer, tear half of the cup away. That produces an ice instrument that can be held by the papered end. The ice end is applied to the injury in a circular, massaging motion for five or 10 minutes. The drill is repeated about every two hours, and icing should continue for two or three days.

Cold constricts blood vessels. That limits bleeding and leaking of fluid from vessels into tissues. Swelling is minimized. Cold also is a pain reliever.

After 48 to 72 hours of cold treatment, begin warm therapy. Heat dilates blood vessels, and that, in turn, brings more oxygen-carrying blood to the injury. The increased flow of blood hastens healing. Moist heat is said to penetrate more deeply than dry heat, so it is the preferred source of warmth. A heated whirlpool is excellent. With it people get the benefits of heat along with the benefits that come from the massage of swirling water. Heat also relieves muscle spasms, a consequence of injury, and it increases the flexibility of tendons and ligaments.

If you want to talk about painful muscles that are part of conditions like sore backs, then the choice is left to the individual. If heat brings more relief, use it. If cold does, then switch to cold.

DEAR DR. DONOHUE: I can do 75 push-ups without stopping. My biceps become sore after doing this exercise. I know push-ups target the chest and shoulders. Why would my biceps become sore? I am 15. How many push-ups should I be doing? – J.K.

ANSWER: To execute a push-up, the hands are on the floor a little past shoulder width. The elbows are kept straight. Body weight is supported by the hands and the toes. From this starting position, the body is lowered by bending the elbows until the chest almost touches the floor. Then the body is raised back to the starting position. Only the toes and hands contact the floor.

Push-ups involve shoulder, chest and back-of-the arm muscles. The muscle on the back of the upper arm is the triceps. The biceps muscle on the front of the upper arm isn’t a major contributor to push-up exercises.

If a woman can perform 44 push-ups, that is considered excellent. If a man can do 49, that is excellent.

Your 75 puts you in a league of your own.

I cannot explain why your biceps ache. Are you sure you have correctly identified the biceps?

DEAR DR. DONOHUE: While playing pick-up basketball with my 12-year-old son, I sprained my ankle. How long should I rest it? – C.B.

ANSWER: Sprains are ligament injuries, and they come in three grades. A grade-1 sprain means the ligaments have been stretched out of shape. The joint still works. A person can move the foot up and down. A grade-2 sprain involves tearing of some strands of the ligament. The swelling is more pronounced than a grade 1. A person can move the foot up and down but with some trouble. A grade-3 sprain occurs when the ligament is completely torn. The swelling is huge, the skin is often bruised, and it is impossible to move the foot.

Grade-1 sprains heal within three weeks after the injury. Grade-2 sprains take up to six weeks to heal. A grade-3 sprain can take as long as six months to fully heal.

You can put weight on the sprained ankle when it does not hurt to do so. It is not a good idea, except in third-degree sprains, to keep the ankle completely immobile.

A grade-3 sprain should be cared for by a doctor. It’s a very serious injury.

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.