"By the time you're thirsty, you're already dehydrated," says Jeanne Grant, a registered dietitian at the University of Washington Medical Center's Nutrition Clinic. To compensate for dehydration, the body increases heart rate due to the decreased blood return to the heart. Restricted blood flow leads to constriction of blood vessels in the skin; this constriction reduces your body's ability to dissipate heat.
To avoid dehydration, drink early and often -- about 2 quarts of water a day. Before exercise, which tends to blunt thirst even more, drink 1 to 2 cups of water. During long hikes and bike rides, try to drink another cup or two every 20 minutes. Avoid alcohol and caffeine, which are diuretics and can dehydrate the body. Sports drinks are okay if you are exercising longer than an hour, Grant says, but in most cases water is fine.
A late afternoon thunderstorm can sometimes do more than ruin a hearty hike or a good round of golf.
Lightning kills up to 200 people a year in the U.S. and most strikes hit in July and August. Golfers on the back nine, swimmers, hikers caught above the timberline, and ball players are a few favorite targets.
Lightning's high voltage -- which seldom causes burns -- can stop your heart and breathing. The heart often starts again by itself, but breathing doesn't. CPR can be a real lifesaver.
Most people who get struck, however, survive, says Brian Zachariah, M.D., of the University of Texas Southwestern Medical School. Survivors can suffer hearing loss, fractures, cataracts, paralysis, memory loss, or even personality change.
To be safe, avoid outdoor exercise in the late afternoon if skies are stormy. Strikes are most common late in the day. Take cover at the first flash, no matter how far away the lightning seems.
If you're caught in a lightning storm, avoid being the tallest object in an open area. Seek shelter or lie down in a low area. If you're on a golf course, don't huddle with your partners or near your clubs under a tree. Lightning traveling down a tree has a "splash effect" that can zap through you and a foursome, says Dr. Zachariah.
Hikers and walkers should lie down in a low spot. Don't hide under an overhang; lightning may curl around the rock to strike. If you are swimming, get out of the water.
We know temperature extremes can make even the perkiest people wilt, but running shoes?
In very hot temperatures (90 to 95 F.), shoe stability suffers, says University of Oregon researcher Barry T. Bates, Ph.D. A stiff shoe becames more flexible, which is bad news for the many runners who require stiff shoes to prevent overpronation. Runners who overpronate (a foot rolls inward) often develop foot and knee problems.
Advises Bates: "If you do a lot of running, are prone to injury, and live in a climate with large temperature differences, switching with the seasons from one type of running shoe to another might prevent injuries."
Shoes with gel- and air-filled components are less affected by temperature changes, says Bates.
Ankles can be a source of angst for weekend athletes. That's because you can easily turn one running down a wide shot in tennis, playing basketball, or trying to run through first base.
High-top athletic shoes can provide extra support, and adhesive taping adds stability. But taping has its limits. A study in the American Journal of Sports Medicine found that, after 20 minutes of intense exercise, tape gives little protection to an ankle.
At least 70 percent of ankle sprains heal in 6 to 12 weeks, says the American Orthopedic Foot and Ankle Society. The best way to protect your ankles is to strengthen them. Here are two easy exercises.
First, sit with your feet dangling above the floor. Turn your feet clockwise and counterclockwise drawing the letter O with your toes, or trace the entire alphabet with your toes.
Second, stand on one foot at a time and raise yourself slowly up on your toes. Then lower yourself. Do this until you feel fatigue. Or, if you like to swim laps, do them wearing fins. Besides helping you swim faster, fins help build strength in ankles.
"Recreational golfers usually don't consider golf a sport, and they don't condition and stretch for it," says Betsy Voyles, P.T., who teaches a golf wellness program in Chicago. Most injuries occur on holes 1 through 4 because golfers don't warm up properly, and on holes 15 through 18 because of fatigue.
Voyles advises arriving at least 20 minutes before tee time to stretch. "Most of us begin with a couple of bad rotations and then we are off. Full-body rotation should be the last thing we do." At the very least, she suggests doing these three stretches before the first tee.
Side stretch. Stand with your arms above your head, holding a golf club in your hands. Slowly bend to the right and take two deep breaths. Then bend to the left and hold for two deep breaths.
Calf stretch. Place both hands against a tree at chest level and stand arm's length away. Keeping your right foot on the ground and the leg slightly bent, move your left foot behind. Press the left heel to the ground until you feel a stretch in your left calf. Alternate legs and repeat.
Trunk and upper body stretch. Hold a club behind your neck, keeping your head and neck straight. Keep your knees slightly bent. Rotate slowly to the right. Hold your position 10 to 20 seconds. Then rotate slowly to the left. Hold your position 10 to 20 seconds. Repeat two to three times.
Parents often tell their kids to "use their heads." When it comes to soccer, that might not be such good advice. A study of 53 Dutch professional soccer players found that hitting the ball with your head too many times may impair memory and recognition skills.
And while very few studies have been done on kids, Dr. Lyle Micheli, of the sports medicine department at Children's Hospital in Boston, believes that no one under age 12 should "head" a soccer ball. Before that age, children's muscles aren't fully developed. He compares the impact of a soccer ball to taking a punch in the face in a boxing ring.
To be safe, Dr. Micheli suggests letting some air out of heavier soccer balls for less impact. Or ask the coach about using a size 4 ball. It's lighter than the professional size 5 ball used by most American kids. European kids play with the smallest and lightest ball -- a size 3 -- and don't move up to a size 5 until they're 18.
It's extremely rare, but about two children die each year after being struck in the chest by a baseball. The most susceptible kids are those between 6 and 9 who weigh under 90 pounds.
Children's ribs are more elastic and less protective than adult ribs. Although it's unclear what exactly causes the heart to stop, doctors think the impact probably disturbs the heart's natural rhythm.
The American College of Sports Medicine, however, says routine use of chest protectors isn't justified based on what's known. But it says catchers at all levels of play should always wear chest protectors and it encourages more research and experimenting with lighter, softer balls.