Stretching too vigorously, holding a stretch too long or stretching until it hurts is not recommended. Stretching should feel good. Static stretching, in which you stretch through a muscle's full range of movement until you feel resistance but not pain, is probably the safest type. Stretch to the point of mild discomfort, at most, and then ease up. If you feel any pain, stop.
Stretch at least three times a week to maintain flexibility. A session should last 10 to 20 minutes, with each static stretch held for at least 10 seconds (working up to 20 to 30 seconds) and usually repeated about four times. Some trainers believe that stretches should be held for one to two minutes, but this is controversial.
Before stretching, always do a brief (5- to 10-minute) warmup, such as jogging in place, brisk walking, riding a stationary bike or doing less-vigorous rehearsals of the sport or exercise you're about to perform. Warming up gradually increases your heart rate and blood flow and raises the temperature of muscles, ligaments and tendons. Stretching cold muscles may injure them, and sudden exertion without a warmup can lead to abnormal heart rate and blood flow and changes in blood pressure. You can also stretch when cooling down after a workout.
For most people, we advise against ballistic stretching—where you do bouncing, repetitive movements while stretching (such as bending forcefully to touch your toes with your knees straight and bouncing). Ballistic stretching may do more harm than good because muscles may shorten reflexively, and, generally, stretching should be gradual and relaxed. However, some professional athletes believe controlled ballistic stretching can better prepare a muscle for sustained activity, especially one requiring a burst of speed.
To stretch opposing muscles in your arms and legs, use static stretches along with the approaches known as active-isolated stretching and proprioceptive neuromuscular facilitation (PNF). In active-isolated stretching, you isolate one muscle at a time and stretch it by contracting the opposite muscle. In PNF, which can be done with or without a trainer or partner, you contract a muscle against resistance (usually provided by another person). You relax, then stretch, while your partner pushes the muscle into a static stretch.
Stretching may benefit your mind as well as your body. When done in a slow and focused manner, an extended stretching routine is an excellent relaxation method and stress reducer (just as yoga and tai chi are). Stretching can help reduce anxiety and muscle tension, as well as lower blood pressure and breathing rate. Note: Don’t hold your breath during a stretch.
Giving yourself time to stretch after you've finished your workout can help keep your muscles from tightening up quickly. It won't, however, head off delayed-onset muscle soreness—the kind that generally occurs the day after unaccustomed strenuous exercise. (In fact, there's no hard evidence that stretching before or after a workout session will prevent injury.) But stretching certainly does promote flexibility and it feels good.