Stretching Makes You Run Slower
If stretching before a run provides no injury prevention benefit, what about performance? Up to a certain point, a longer muscle is a more powerful muscle, so it stands to reason that stretching to lengthen the muscles prior to a run might improve performance. Here again, recent research has found just the opposite to be true.
Writing for the American College of Sports Medicine in a 2014 paper titled, "The Effects of Stretching On Performance," researchers found that performing either static or PNF (assisted, "contract-relax") stretching immediately prior to exercise led to worse performance for both distance runners and sprinters. Dynamic stretching fared better, actually improving performance among speed and power athletes, but there is no conclusive evidence to date about whether it helps or hinders endurance sport performance.
Why Stretch at All, Then?
Since stretching immediately before a run hampers performance and doesn't prevent injury, it would seem there's no good reason to ever stretch. But what this new evidence ignores are the very positive benefits of a regular, long-term stretching program. Indeed, research has found a long-term, regular stretching regimen can improve performance, and there are other benefits to consider as well.
In its most recent position paper on exercise guidance, the American College of Sports Medicine states that flexibility training is essential for maintaining or improving joint flexibility and range of motion, and this becomes increasingly important as we age. In order to stay limber and agile, the ACSM recommends stretching at least two or three times per week. And it doesn't seem to matter which type of stretching you prefer--the research indicates that you can get nearly the same benefit from static, PNF or dynamic stretching.
Because your muscles must be thoroughly warmed up prior to any type of stretching, the perfect time to incorporate your flexibility training is immediately following your easy runs. For static or PNF stretching, hold each stretch at the point of tension--but not pain--between 10 and 30 seconds. Relax and repeat up to three times.
For dynamic stretching, the ACSM advises that you incorporate slow movements that involve "a gradual transition from one body position to another, and a progressive increase in reach and range of motion as the movement is repeated several times."
