DEAR DR. DONOHUE: You discussed headaches following basketball or exercise. Have you considered dehydration and the loss of electrolytes as a cause? Restoring hydration with plain water is another possible cause. People need electrolytes. Gatorade is my drink. – R.W.

ANSWER: You bring up some important points. Dehydration can be a cause of exercise-associated headaches. Dehydration happens when fluid intake doesn’t equal fluid loss, chiefly from sweating. You can determine how much fluid is lost during any particular exercise session by weighing yourself before and after exercise. The weight lost during exercise isn’t fat. It’s mostly fluid. A 2 percent weight loss puts you on the dry side.

Dehydration can affect performance greatly. If a 2 percent to 3 percent (perhaps even 1 percent) weight loss occurs during a game or practice and is not corrected with fluid, an athlete’s skills suffer. This has been clearly shown with basketball players. When compared with players who stayed hydrated, players who suffered from dehydration lost shooting accuracy and were less able to sprint, and their agility disappeared. The same kinds of things were demonstrated in semipro soccer players. If anything catches a coach’s attention, it’s loss of performance.

You also make a point of the fluid used to replace sweat losses. Sweat contains electrolytes — sodium, potassium and chloride. In long-duration events, like running a marathon, replacing sweat loss with water presents a danger of brain swelling. On a few occasions, it has caused death.

Sports drinks like your favorite contain carbohydrates and electrolytes. The carbohydrates are a source of energy. If a person or school finds them too expensive, it can make its own sport drink with a 5 percent solution of sugar water to which salt has been added.

For events lasting less than two hours, water is a safe replacement fluid.

DEAR DR. DONOHUE: In 30 years of reading about and leading exercise, I always thought that stretching exercises should be held for 30 seconds to be effective. Recently on the radio, I heard an expert say that stretches should be done in repetitions of one or two seconds. Is this correct? – R.R.

ANSWER: It’s claimed that stretching increases a joint’s range of motion and lessens the risk of injury. I can buy the motion idea. I have trouble buying the injury-protection one.

Some athletic endeavors require great flexibility, and stretching is essential for those sports – gymnastics, swimming and dancing.

The length of time to hold a stretch varies with the article you happen to read. It’s hard to believe that a one- or two-second stretch does much for muscles or tendons. A stretch time of 10 seconds is a safe amount of time to start a program. With experience, the stretch can be held as long as 15 to 30 seconds. Some maintain that a 15-second stretch does as much good as a two-minute stretch, not that two minutes should be anyone’s goal.

This is an issue on which there is no universal agreement.

DEAR DR. DONOHUE: I started dieting and joined a popular gym for women. When I joined, I was told that if I did not stretch after a workout, I would lose 60 percent of the benefit from the workout. I joined another gym and asked if that was true. The trainer said she was never told such a thing. Now I am confused. Is it necessary to stretch after a workout to retain its benefit? – C.I.

ANSWER: I can’t imagine why.

If you can contact your first source, ask the reason why she believes this and let me know.

DEAR DR. DONOHUE: Your answer to exercise for those with COPD (chronic obstructive pulmonary disease – emphysema and chronic bronchitis) is incomplete. You should mention pulmonary rehabilitation programs. They are available in many communities and at many hospitals. – C.G., M.D.

ANSWER: You’re right, doctor. Pulmonary rehabilitation programs are most helpful for COPD patients. The training is done under supervision, so it is safe as well as effective.

DEAR DR. DONOHUE: Please write about dystonia, a terrible disease to which there appear to be no answers. My sister suffers from it. – L.G.

ANSWER: Dystonia comes in several varieties. The common feature of all is painful, sustained muscle contractions. Some dystonias are limited to one or a few muscles. For example, dystonia limited to eyelid muscles causes excessive blinking to the point where the lids can be locked tightly closed. This makes the person virtually blind. The condition is called blepharospasm. Dystonia of neck muscles draws the neck to the side, front or back, and locks it there. This is torticollis or wry neck.

Dystonia of many muscles can leave people contorted in awkward, uncomfortable positions for extended periods of time.

The cause of dystonia isn’t known. Some varieties are inherited. And some dystonias are misdiagnosed for years and years. Dystonia in childhood can be mistaken for cerebral palsy.

Although a cure isn’t at hand, medicines that affect the transmission of the muscle-activating body chemical acetylcholine help some patients. Parkinson’s disease medicines have also found a place in dystonia treatment. Deep brain stimulation – the electrical stimulation of wires implanted in the parts of the brain controlling muscle activity – has freed some dystonia patients from the grip of twisted postures imposed by dystonia. Botox has been a boon to many patients, especially those with limited forms of dystonia.

Your sister should contact the Dystonia Medical Research Foundation for the helpful information it provides. She can contact the foundation at 800-377-3978. The foundation’s Web site is www.dystonia-foundation.org.

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 www.rbmamall.com