Research in this area has looked at two main areas: pre-exercise stretching and injury prevention; and the effect of stretching exercises on the force production and power output of muscle.
Contrary to popular belief, there is no real evidence to suggest that acute, static pre-exercise stretching – on its own – prevents injury.1, 2 The problem is that injury during exercise or training can be due to many factors and decreased flexibility in a normal, healthy population is relatively low down on the list. Of course, if someone has a limited range of motion, or perhaps aberrant movement mechanics that can be improved with appropriate stretching exercises prior to working out, then stretching is clearly good for them.
Secondly, there is a growing body of research that appears to indicate that acute, static pre-exercise stretching can decrease muscle force and power production; in some experiments by as much as 30%.3 Other studies have also shown significant decreases in vertical jumping performance (on average around 2.5%) following an acute bout of stretching.2 It is not entirely clear precisely what is going on, but more than likely this decrease in performance is due to a decrease in muscle ‘stiffness’ (and in the stored elastic energy component) that compromises the ability of muscles to act as semi-rigid springs during high force, power and jumping actions.
The type of stretching that seems to be most problematic is acute, static or modified PNF (proprioceptive neuromuscular facilitation) stretching, performed with a view to increasing range of motion, carried out prior to strength, power or jumping training. Appropriately executed ballistic stretching techniques, following a suitable warm-up, have not been shown to be detrimental to muscle performance.
So what should you do?
If you need to improve range of motion in order to safely perform certain exercises, then you need to make sure that you do this. The current consensus opinion in the research literature4 is to do an exercise or event-specific warm-up before introducing suitable dynamic movements that progressively increase in intensity and range.
Stretching techniques and exercises designed to increase an existing range of motion should be performed at the end of a workout or as a separate session elsewhere in the training programme where it will not interfere with muscle force or power production.
This feature was first printed in the June/July 2011 issue of Fitpro Network magazine.
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The views and opinions expressed in this article are those of the author and not of Fitness Professionals Ltd or Virtual Magazine. Consult a qualified health or fitness professional before making changes to your diet or exercise.