Stretching should be an important component to any runner’s routine. Runners tend to be tight in predictable areas (most notably the hamstrings and calf muscles) and in turn, they get injured in and around those areas.
Do not do static stretches (holding an elongated muscle in a fixed position for 30 seconds or longer) before running. Stretching is best done after a warm-up period of 10 to 15 minutes after your muscles are warm, or at the end of your workout.
An important note about stretching after long runs (longer than 15 miles): Do not stretch immediately following your run. Your muscles have hundreds of micro-tears in them and stretching them could turn some of these into macro-tears, causing significant damage. Instead, cool down, take a shower, eat a good meal and drink plenty of fluids. Then it is okay to stretch later in the day.
There are a few rules when it comes to stretching. First, pain is never acceptable. Stretching should be comfortable and relaxing, never painful. If something hurts, you’re not in the right position or you’ve stretched too forcefully. Back off and check your position, then try again more gently. Second, move slowly into each stretch and don’t rush it. Once in position, hold steady for about 30 seconds and do not bounce. Finally, be consistent. The more consistently you stretch, the more effectively you will be in increasing your flexibility. Stretching daily initially and later three times a week for maintenance is a good rule of thumb.