Here's an interesting follow up post to the one we did on 25 November this year on how necessary stretching was and how stretching affects performance and whether it can prevent exercise related injury on 23 February 09 in our other blog.
It's well established from previous published research that an acute bout of stretching can affect your maximum strength levels. Well, here is what I read from a study which examined how stretching affected strength levels.
The subjects in the study performed a one repetition test of maximum knee bending (or hamstring) strength after performing various numbers (ranging from 0-6) of hamstring stretches for 30 seconds. Here's what they found. It took only 1 stretch (of 30 seconds) to reduce their maximum strength! And what's more, additional bouts of stretching further affected strength levels. So, if you're trying to run fast or participate in an event which requires you to exert huge efforts don't stretch before that.
Winchester JB et al (2009). A Single 30 Second Stretch Is Sufficient To Inhabit Maximal Voluntary Contraction. Research Quarterly for Exercise and Sport. June 80(2) : 257-261