Is stretching even helpful?
Runners are dogmatic about stretching. It's the cause of everyone's problems. "If only I had stretched more this darn Achilles wouldn't be acting up." Maybe - but more likely, stretching plays less of a role than people think.
Why do we stretch: besides the answer - "because it's what we've always done," stretching is believed to 1) reduce risk of injury by decreasing muscle stiffness or increasing muscle compliance and 2) improve performance by having an optimal ROM, freer movement pattern.
What does stretching actually do? Stretching, done long enough, does improve your range of motion and makes muscles more stretchy. For about 8 minutes*. It does this by decreasing motor neuron excitability (neural effect) and a visco-elastic effect - or - the soft-tissue itself becoming more malleable.
How long: the sweet-spot seems to be between 4 sets of :60 to :90 seconds. 2 sets of :45 seconds had no significant effect on range of motion.** Yeah - that's a long time to stretch those hammys.
The problem: stretching actually impairs strength and power output. You may be more bendy, but that decrease in motor neuron excitability has also decreased your ability to produce power. Not ideal if you're about to dodge cars in Midtown.
Stretching: Final Words (for this week...) there's nothing wrong with it. I would save it for after the run, if you have time, but don't expect that flexibility to last more than an hour. It feels good, it can be helpful, but not as important as we continue to believe.
Next week: things to do that are more effective & time-efficient for performance and injury prevention.
* Ryan et al (2008) 4x:30 sec stretch program reversed after 8 minutes
**Magnusson (2002) 2x :45 sec stretch had no significant effect
Source: To stretch or not to stretch: the role of stretching in injury prevention and performance. McHugh MP, Cosgrave CH.