Some people needn’t bother with stretching. If you have good biomechanics, don’t spend a lot of time in front of a computer, and have the kind of lifestyle where you can nap or take a dip in the ocean whenever you want, you might be one of them. Otherwise, stretch.

Focus on the “runner’s five”: 

1. Hamstrings
2. Hip flexors
3. Quadriceps
4. Calves
5. Iliotibial (IT) band, or connective tissue that runs from your hip down the outside of the leg. 

These are the muscle groups that tighten even when people aren’t running, from bad posture, sitting, repetitive activities, and just living. Though there are myriad exercises to choose from for each area (I suggest The Whartons’ Stretch Book for clear instructions and diagrams), what’s important is to do them correctly and regularly.

For example, to stretch the hamstring, lie flat on your back and loop a belt or piece of rope around the ball of one foot, holding the ends of the rope in each hand. Keeping your legs straight, lift the roped leg (without pulling on the rope) as high as you can. Keep lifting until you feel a slight stretch in the back of the thigh, then use the rope to pull until the stretch is slightly—but just slightly—deeper. The stretch should be neither difficult nor painful. Hold for 2 seconds. Then relax and lower your leg to the floor. Repeat five to ten times.

This exercise uses the Active Isolated Stretching (AIS) technique, which I prefer and which is quick (you can do your daily routine in 5 to 10 minutes), easy, and effective. Whether you stretch before exercise or after (as I do), using the active isolated technique, there’s no excuse not to stretch.”