In addition to recommending exercise for general health and well-being, doctors may prescribe specific exercise plans in some situations. Before elective surgery, doctors may recommend people participate in exercise routines to enhance their recovery from surgery. Doctors also prescribe specific exercise programs to rehabilitate people after serious injuries or disorders such as heart attacks, strokes, major surgery, or injury (see Overview of Rehabilitation).

FIT TIP: To trim your tummy, do fewer crunches and more planks: Begin on all fours, hands under shoulders, knees under hips, then lower forearms to floor and extend legs straight behind you, balancing on toes. Keeping abs engaged and back flat, hold for 30 seconds; do 10 reps three or four times a week. Limit crunches to no more than three sets of 15 at a time. Anything beyond that isn't doing you much good, experts say.
Get in plank position with your hands wider than shoulder-width apart (A). Lower your chest as close to the floor as you can. Holding that position, lift your right knee to the outside of your right elbow (B). Return to plank position, then push back up to start; repeat on the other side. That's one rep. Do three sets of 12 to 15 reps, resting for 30 seconds between sets.

The skin also serves as a release point for heat. (See “Why Does My Face Turn Red When I Exercise?” for more on that.) When you exercise, your muscles generate a lot of heat, which you have to give up to the environment so your body temperature doesn’t get too high, Hackney says. The heat in the muscle transfers to the blood, which shuttles it to the skin; it can then escape into the atmosphere.

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