If you run, you probably stretch. You've heard it's good for you and it just feels right. But when you stretch can be as important as how and when you stretch.
A review of various studies on the effect of pre-workout static stretching on strength, power and explosive performance found a negative rather than positive effect — especially when each stretch is held longer than 45 seconds. It's believed that this "overstretching" of muscles may fatigue them, by weakening the muscle-tendon connection, before they get the chance to start working on a run. Pre-run stretching has also been found to have a negligible effect on injuries.
Sports scientists and coaches, however, have learned that stretching, especially "dynamic" stretching (stretching while moving), is relatively safe and may have a positive effect on performance after your muscles are warm. This assumes that you perform stretches correctly: stretch to the point of pressure, not pain, during static stretches. Here's when you can most effectively slip in some stretches:
After Easy Runs
After easy runs — when the muscles are warm, but not overstressed — is a great time to do some stretches (static or dynamic). This has the added advantage of gradually letting your heart rate return to normal. Be sure to stretch the hamstrings, the muscles you work hardest when you run. The simplest hamstring stretches involve reaching for your toes with one hand at a time, while standing (with one leg elevated on a bench) or sitting on the ground (seated hamstring stretch).
After Hilly Runs
Whether it's after hill repeats or a distance run over long or numerous hills, stretching after these runs should emphasize the muscles most involved on both descents (the hamstrings) and ascents (the calves and quadriceps). A simple calf stretch is to stand with your forefoot above a step or curb and slowly, gently drop your heel until you feel the stretch. This also stretches the Achilles tendon, which works hard on hills. Also do Standing Quad Stretches: pull the back of each foot toward your butt.
Stretching after you've jogged a few laps on the track--but before you start doing "strides" or intervals — is a good time to stretch the muscles when they're warm, but not yet fatigued. This is especially valuable if you're doing "short" speed, such as 200-meter repeats, which are easier with flexible muscles. Dynamic stretches are best. These typically involve rotating your joints — hip circles, shoulder circles, neck circles, arm swings--and light "plyometric" exercises like "high knees" and "butt kicks."
Gym Workout Stretching
Cardio machines should always be used before strength training at the gym, and the best time to stretch (static or dynamic) is between the two — when your legs are warm, but before they're fatigued by lower-body strength exercises or equipment. Note: Watching online videos of stretches is the best and easiest way to learn how to correctly perform stretches.
Mornings or Evenings
Light stretching when you get out of bed in the morning or before you go to bed at night, such as in front of the TV, can be worthwhile. But keep it light. Don't reach too far into stretches and don't hold stretches for longer than 30 seconds. Keep these stretches simple. Stretch the way a cat does after napping: a few seconds stretching out the paws and it's ready to chase mice. Gentle and relaxed static stretching has been proved effective to widen motion range, especially when done after a bath or shower (when muscles are warm).