Too much STRETCHING can make you WEAKER!!
Warning! Too much stretching can actually make you weaker...
Prolonged stretching before exercise can actually reduce muscle strength.
Researchers from the Department of Kinesiology at Canada's McMaster University measured muscle strength in the soleus (pronounced so-lee-us ??? you'll find it at the back of your lower leg) following 30 minutes of stretching.
The table below shows you how muscle strength changed following the stretching procedure:
Minutes After Stretching Drop in Strength
Immediate - 28%
5 minutes - 21%
15 minutes - 13%
30 minutes - 12%
45 minutes - 10%
60 minutes - 9%
As you can see, muscle strength dropped by almost 30% immediately following the stretch. Even one hour later, soleus had still not returned to "full strength".
So does this mean you should you avoid the pre-exercise stretch altogether?
Not exactly.
Think about it from an evolutionary standpoint. If your stone-age ancestors needed to stretch before killing their next meal, they probably wouldn't have survived very long.
Now, that isn't to say you shouldn't bother warming up before you train. But make your warm up specific. If you're about to train with weights, then warm up by lifting lighter weights. And a small amount of stretching won't damage your performance ??? after all, subjects in this study were stretching virtually non-stop for 30 minutes.
But if you're planning to do a lot of stretching, make sure to do it AFTER you train.
Reference
Fowles, J.R., Sale, D.G., & MacDougall, J.D. (2000). Reduced strength after passive stretch of the human plantarflexors. Journal of Applied Physiology, 89, 1179-1188