Half-truths can turn your exercise regimen into an injury trap.

Don’t believe everything you hear when you are trying to get in shape or stay in shape. There are plenty of myths and half-truths.

Among the most dangerous fitness myths to avoid…

FITNESS MYTH #1: A little pain means you’re getting maximum benefit from your workout. Despite the popular cliché “no pain, no gain,” you should never feel prolonged, stabbing or sharp pain during a workout or continue to exercise when something hurts.

The risk: Pain means damage. It could be a warning sign that you have overstressed or overstretched a muscle, tendon or ligament. It also can indicate joint damage. People who continue to exercise when they hurt risk more serious injuries, such as torn muscles or tendinitis (inflammation of a tendon).

Exception: A little soreness after exercise means that you have had a good workout. When you exercise hard, the muscles develop microscopic tears that lead to rebuilding of tissue and an increase in strength. If you are very sore, however, you have overworked your muscles.

Warning: Don’t believe the myth that you can exercise longer and harder if you take an anti-inflammatory pain reliever, such as ibuprofen (Motrin), before going to the gym. Taking a preworkout anti-inflammatory may reduce muscle performance and prevent you from feeling an injury while working out.

Important: If you have arthritis or another painful condition that requires daily treatment with aspirin, ibuprofen or another anti-inflammatory medication, ask your doctor if it’s safe to take the drug prior to workouts. The combination of exercise and anti-inflammatories might increase the risk for damage to the gastrointestinal lining, according to new research.

FITNESS MYTH #2: You should stretch before exercising. Trainers used to advise everyone to stretch before lifting weights, going for a run, etc. Do not do it.

The risk: Tendons and ligaments take longer to warm up than muscles. People who stretch when they’re “cold” are more likely to suffer from muscle and tendon strains and other injuries than those who begin their workouts with a progressive warm-up. Static stretches, in which you stretch a muscle to a point of tension and hold the stretch for a certain period of time, can be particularly harmful before a workout.

Recent finding: New research also has shown that people who do static stretches before working out can’t exercise as long and may have reduced muscle strength.

Exception: You can start a workout with dynamic stretches, slow movements that mimic the exercise patterns you’re about to do. Before taking a run, for example, you could do some fast walking and slow jogging. This type of stretching is safe and prepares the muscles for exercise.

Also: Stretch after vigorous activity. That’s when muscles and tendons have the best blood flow and elasticity, and you’re less likely to get injured. Good postworkout stretches…

  • Figure Four. Sit on the floor with both legs out in front of you. Bend your left leg, placing the sole of your left foot against your right inner thigh. With your right hand, reach for your right ankle and hold for 30 seconds. Perform twice on each side to stretch your hamstrings and calves.
  • Letter T. Lie faceup on the floor with your arms in a T-position. Slowly cross your left leg over your body, allowing your torso to rotate so that your left foot is near your right hand. Keep your leg as straight as possible. Hold for 20 seconds. Perform twice on each side to stretch your hips and lower back.

FITNESS MYTH #3: Do not rest during workouts. You have probably heard that the best strength-training workouts involve nonstop action, with no rest (or very little rest) between exercises.

The risk: Failing to rest will cause muscle fatigue and poor form, a common cause of injuries. Also, you won’t fully train the muscles because they need time to recover.

When you’re working the same muscles, you need to rest 30 to 90 seconds between sets. Example: Do eight to 12 biceps curls…take a 30-to-90-second break…then curl the weight again.

Exception: With circuit training, you move quickly from one exercise to the next. You might do a biceps exercise, then a leg exercise, then return to the biceps. Even though you’re constantly moving (and getting a good cardiovascular workout), you’re allowing one group of muscles to rest while you work a different part of the body.

FITNESS MYTH #4: High-heat exercise works the muscles more. Some people believe that high-temperature workouts—including “hot” yoga, spinning and others in which the room temperature may be 90°F or even hotter—make the muscles more limber and improve the body’s ability to remove toxins.

I do not recommend it. For the average person, exercising in high temperatures will reduce their performance because the body has to work harder to fend off the heat.

The risk: It forces the heart to do double-duty—not only to bring oxygen to the muscles and remove wastes that accumulate during exercise but also to pump more blood to the skin to dissipate the extra heat. If you’re tempted to try high-heat workouts, ask your doctor first.

SAVE YOUR BACK

“Core”-strengthening exercises help prevent low-back pain by strengthening abdominal and back muscles. However, one of the most popular of these workouts, which involves lying on your back and simultaneously raising both legs in the air, causes a pronounced arch in the low back that can trigger—or worsen—low-back pain.

Better: Bicycle maneuver. Lie with your lower back pressed against the floor, your hands clasped behind your head and your knees bent. Simultaneously lift your head and shoulders off the floor. Bring your left knee to your right elbow, while straightening your right leg. Using a bicycle-pedaling motion, alternate sides. Extend your legs as far as you comfortably can without arching your back. Typical number of reps: 10 to 15 times on each leg with slow and controlled movements.