Some of you may already know that I’m allergic to exercise.  It’s a character flaw that I’m working on.  Anyway, whether in or out of gym class, I grew up learning that you’re supposed to stretch before really going at it with the running, or the jumping, or the hopping, skipping, twirling,…whatever it is that people do to fit into their jeans.  But it turns out that the kind of stretching you’re most likely familiar with is usually NOT the thing to do before you go hardcore with the exercise.

And what kind of stretching is that?  There are basically 2 kinds of stretching: static and dynamic.  You know when you sit on the floor with your legs in front of you and you try to touch your toes?  Or when you stand and try to pull your foot behind you as far back as you can?  Or those side-to-side stretches that the little kiddies are doing in the picture up there?  These are all examples of static stretching – meaning you’re holding positions for 20-30 seconds.

The problem with static stretching is that it actually WEAKENS your muscles.  Yep.  No lie.  I combed through the studies and it’s true: most studies show that if you, for example, statically stretch your legs before jumping, you don’t jump as high.  You actually jump higher if you DON’T stretch statically.  Not only that, muscles that have been statically stretched can stay weakened for up to 30 minutes, which is how long a lot of workouts are.  So not exactly ideal.

Dynamic stretching doesn’t have this problem.  In this kind of stretching, your body is always moving, just at a much lower intensity level, like light jogging for instance.  There are 2 reasons dynamic stretching is better: it increases both flexibility and power.

For those who are interested in the sciencey bit – flexibility increases because your muscles and tendons are loosened, thus increasing your range of motion.  This is important because you’re less likely to suffer an injury if you wind up extending yourself more than you’re used to.  Power increases because you’re literally warming up your body by elevating the temperature.  This causes your blood vessels to dilate (the passageway gets bigger), which increases blood flow.  More blood flow means more oxygen is delivered to your muscles.  This is important when you’re exercising because your muscles need oxygen to get the energy it needs from the food you eat.  (Cellular respiration and mitochondria anyone?  Anyone?  Where my bio peepz at?  Holla!)

The key with dynamic stretching is to hit the sweet spot of timing and intensity.  You don’t want to stretch too early or else your muscles will stiffen up by the time you get to the actual workout.  You also don’t want to go too hard with the stretching or else you’ll tire yourself out before you ramp things up.

So what’s the sweet spot?  For the timing, your warm-up should last about 5-10 minutes, and you should give yourself 5 minutes to recover before starting the hardcore exercise.  For the intensity, if you decide to jog lightly, then you want to jog so that your heart rate is 40% of your maximum heart rate and progresses to about 60%.  (Heart rate is the number of times your heart beats per minute.  To figure this stuff out, you need to measure your heart rate at the peak of your workout, and then take 40% of that – meaning, multiply by 0.4.  Where my math peepz at?  Holla!)

When it comes to dynamic stretching, it’s not a one-size-fits-all type of thing.  You should tailor your stretching so that it best prepares you for the type of intense activity you’re about to engage in.  So runners would have a different stretching regimen from swimmers.

To see some examples of dynamic stretching, read this article.

Also, it seems that how much stretching prevents injury depends on the activity.  If you’re going to be doing a lot of stop-and-go, jumping, bouncing types of activities that require quick bursts of power and a lot of shock absorption, then dynamic stretching is more important.  But if you’re just going for a run (not sprinting), stretching seems to have less of an effect, if at all, on injury prevention.  Dynamic stretching also seems to improve performance if you do it regularly before your workouts, as opposed to once in a while.

So does this mean that static stretching is completely useless?  No.  Any kind of stretching loosens up your muscles and tendons, so you wind up increasing your flexibility.  Also, certain types of static stretching may improve balance, as long as the positions aren’t held for too long (more than 15 seconds).  But other than that, if you’re about to do something that requires a lot of muscle power, in addition to flexibility, then dynamic stretching is the way to go.

And that concludes this edition of the health blog.  And to show you that I’m not making this up:

1. Effects of Dynamic and Static Stretching on Vertical Jump Performance and Electromyographic Activity.  2009.  PubMed ID: 1920457
2. The acute effects of different durations of static stretching on dynamic balance performance.  2009.  PubMed ID: 19077736
3. Pretesting static and dynamic stretching does not affect maximal strength.  2008.  PubMed ID: 18841081
4. A systematic review into the efficacy of static stretching as part of a warm-up for the prevention of exercise-related injury.  2008.  PubMed ID:  18785063
5. Negative effect of static stretching restored when combined with a sport specific warm-up component.  2008.  PubMed ID: 18768355
6. Acute effects of static and ballistic stretching on measures of strength and power.  2008.  PubMed ID: 18714248
7. Acute effects of static, dynamic, and proprioceptive neuromuscular facilitation stretching on muscle power in women.  2008.  PubMed ID:  18714235
8. Effects of stretching on upper-body muscular performance.  2008.  PubMed ID: 18545177
9. Four-week dynamic stretching warm-up intervention elicits longer-term performance benefits.  2008.  PubMed ID: 18545176
10. Warm-up and stretching in the prevention of muscular injury.  2007.  PubMed ID: 18027995
11. Stretching and injury prevention: an obscure relationship.  2004.  PubMed ID: 15233597
12. Does stretching improve performance? A systematic and critical review of the literature.  2004. 15377965
13. Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review.  2002.  12202327
14. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature.  1999. 10593217