You have probably listened to at least one person tell you that you need to stretch before you run. And you've probably done it, maybe you still do it religiously. The truth is, static stretching is not an optimal way to warm up before you run. In fact, you can actually strain your muscles by doing so and making your muscles weaker before a long run.
It doesn't. Warming up is what prevents injury and static stretching is not in that category. When you slowly increase your blood flow, you give your muscles a chance to prepare to run. Most injuries occur within the normal range of motion, so trying to stretch beyond that before a run doesn't make any sense. Florida State researchers found that stretching before a run makes you about five percent less efficient! That means you have to burn more energy to run at the same pace.
However, research has shown that a warmup routine focussed on the goals of the upcoming activity actually does provide decent insurance against the number and severity of both accidents and overuse injuries.
Delayed onset muscle soreness (DOMS) is that insidious deep tenderness you can feel after a hard workout. Most research on DOMS has shown that stretching before a workout results in no significant improvement in muscle soreness. Stretching can feel amazing, but it doesn’t make the soreness go away, or speed up recovery. The same applies for stretching after a workout. The only thing that relieves DOMS is time!
This doesn't mean you should forego stretching completely. There are tons of benefits to stretching, such as helping an area of inflexibility that is causing an injury or if you have an inability to complete a task because of a lack of range of motion, stretching can be useful. However if you’re about to go for a run, it's best to save stretching for after and practice dynamic stretching as part of your pre-run warm up!