Flexibility is a common health marker in many fitness settings.
Yoga, with its endless stretching and breathing routines, carries a certain glory with it -- although seeing some guy or girl tying him or herself into a pretzel makes my head hurt. Certainly that's an impressive feat, and one I could never hope to mimic. But should I be trying to, and what about my clients? Given the science, I'm going to have to give an honest and resounding "no."
We've already seen an article on the PTDC advocating trainers not to perform passive stretches on their clients, (1) and I couldn't agree more. Stretching carries with it a non-insignificant potential for injury, and that risk is only increased when the trainer is at the wheel rather than the client. If you're responsible for that injury, it could mean extremely unwanted legal complications. From a business standpoint, that's an unnecessary risk.
So should clients even be bothering to stretch? Let's examine the arguments for and against flexibility training. We'll start with the myth busting.
What isn't stretching good for?
Stretching as injury prevention.
Stretching as injury prevention has been well studied, but the results are extremely mixed, and show minimal efficacy either way. A research review back in 1999 studied twelve separate studies and found no consensus on the effect of stretching. Further, it was noted that three of the four studies that noted a positive benefit in terms of injury prevention were confounded by the inclusion of a traditional warm-up alongside stretching (2). The result is that there's very little evidence that stretching has any positive ability to prevent injuries.
Stretching as muscle soreness prevention.
Stretching can't prevent DOMS (3, 4).
Many people will insist that they feel an acute reduction in DOMS from stretching, though this may be more psychological than physical. Chris Beardsley assembled a list of effective modalities for treating DOMS, and stretching was not listed as one of them, suggesting that the research isn't there (5).
However, it's important to understand that stretching probably works largely on the principle of "diffuse noxious inhibitory control" (DNIC). DNIC refers to the ability of your brain to inhibit pain in one area of the body when another is actively in pain. In short, by inducing the pain of a stretch, you can cause the body to temporarily focus on that instead of the area that's actually sore.
Of course, this doesn't last very long, and would need to be repeated regularly throughout the day. But it does work, as do similar things like massage, foam rolling, hot/cold therapy, etc.
Stretching as a warm-up.
The main purpose of any warm-up is to reduce the risk of injury and prepare the athlete for the task at hand. Multiple published papers by TorbjÃ¸rn Soligard et al. examined the effects of a dynamic warm-up on female soccer players and found drastic reductions in injury rates over a large sample (6, 7). However, as seen above, stretching doesn't reduce injury rates.
Further, stretching can acutely reduce performance (8). While the effect is minimal and dose dependent, meaning that most exercisers would see little to no effect on their performance, it's important to understand that too much stretching (greater than one minute per stretch) will definitely decrease performance.
Sure, stretching gets the blood flowing and will raise core temperature somewhat, but so will walking/jogging before a run, doing lighter sets before heavier ones, dynamic warm-ups, etc. Chances are, given the above evidence for active warm-ups, that these would be a better option than stretching.
Stretching to improve flexibility
Stretching does improve flexibility, in terms of range of motion and joint angles at maximum stretch.
However, it's important to ask ourselves "for what reason?" If a client's major goals are health and fitness, chances are they don't need a huge range of motion for anything. Elite athletes and gymnasts do require flexibility, but only enough to do what their sport demands of them. In other words, you need only enough flexibility to do what you need to do -- and for many people, that's not very much!
Now, let's move on to what does hold up.
What is stretching good for?
Stretching is beneficial for the heart.
A study by Farinatti et al. found that stretching has some positive effect on heart rate variability in untrained subjects (9).
This shouldn't come as too much of a surprise. After all, all movement is exercise and all exercise benefits the heart to some extent. Of course, I'd argue that there are plenty of better ways to benefit your heart through exercise, and certainly plenty of ways more cost-efficient for your clients' time.
Stretching induces hypertrophy.
Yes, it's a study on rats (10). Still, there's evidence that stretching improves muscle size. Any movement of a muscle can induce hypertrophy, and the main factor in hypertrophic growth is time under tension. This may not be the best use of your time if you're looking for hypertrophy, since heavy weights will stimulate more muscle and lead to better muscle gains.
Furthermore, you'll also probably see an increase in strength, since bigger muscles are typically stronger given equal levels of training. This is probably why people who do yoga as their primary form of exercise gain strength, even though they don't do any real strength training. I'll repeat, there are probably better ways to improve strength out there.
Since there's no progressive overload in the equation, the only variable you can modify is time, and with diminishing returns that means you're soon putting massive amounts of time in for only minor strength gains.
Stretching does make you more flexible, even if it's not permanent and probably not a huge difference.
Some people simply enjoy being flexible, train for a flexibility-based sport, or like being able to perform feats of flexibility, and in this case, stretching is for you.
A major reason why we used to think all the things we did about flexibility was that our primary understanding of the stretch modality was physical in nature. But physical adaptations don't seem to change here. Cited from a paper by Weppler and Magnusson:
"Increases in muscle extensibility observed immediately after stretching and after short-term (3 to 8-week) stretching programs are due to an alteration of sensation only and not to an increase in muscle length. This theory is referred to as the sensory theory throughout this article because the change in subjects' perception of sensation is the only current explanation for these results." (11)
What does this mean? It means that adaptations to stretching are largely neurological in nature, and not physical. That explains why it doesn't have many of the physical benefits (injury prevention, DOMS reduction, permanent flexibility) that we attribute to it. Stretching thus results only in neurological adaptations, which improve pain tolerance and reduce the onset of pain in a stretching individual.
This also explains why it's so well suited for yoga -- the combination of flexibility with mentally focused breathing and mindfulness seems rather natural if they're all neurological pursuits. Of course this is a double-edged sword -- this pain only exists to prevent potentially injurious over-stretching, which means that the frequent stretcher puts him/herself at an increased risk for injury.
Given all of the above, I would not make any of my clients do static stretches. There could be some use for postural therapy and high-level athletes, but even then most trainers rarely work with these populations. Postural therapy is better left to physical therapists, if it needs to be performed at all, and most trainers work with health and wellness clients.
Stretching certainly has plenty of benefits, but there are also plenty of better ways to train for those benefits without eating up as much of your clients' time. It's not that stretching is useless, just that it's not cost-efficient.
If clients want to tie themselves up into a pretzel, chances are that as a trainer you don't have the specialized skills to help them do so. Otherwise, there's not much point to forcing clients to tie themselves up if they don't want to and won't get much out of it.
I still stretch daily while I watch television, but not because I think I need to - rather because, in the end, stretching just feels good.
(1) Mcatee, Should Personal Trainers Stretch Their Clients?. http://www.theptdc.com/2013/08/should-personal-trainers-stretch-their-clients/
(2) Shrier I., Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature. http://www.ncbi.nlm.nih.gov/pubmed/10593217
(3) Herbert and Gabriel, Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. http://www.bmj.com/content/325/7362/468
(4) Lund et al., The effect of passive stretching on delayed onset muscle soreness, and other detrimental effects following eccentric exercise. http://www.ncbi.nlm.nih.gov/pubmed/9764443
(5) Beardsley, What methods help improve recovery? http://www.strengthandconditioningresearch.com/2013/11/07/recovery-methods/
(6) Soligard et al., Comprehensive Warmup programme to prevent injuries in young female footballers: cluster randomized controlled trial. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600961/
(7) Soligard et al., Compliance with a comprehensive warm-up programme to prevent injuries in youth football. http://bjsm.bmj.com/content/44/11/787.long
(8) Kay AD and Blazevich AJ, Effect of acute static stretch on maximal muscle performance: a systematic review. http://www.ncbi.nlm.nih.gov/pubmed/21659901
(9) Farinatti PT et al., Acute effects of stretching exercise on the heart rate variability in subjects with low flexibility levels. http://www.ncbi.nlm.nih.gov/pubmed/21386722
(10) Kamikawa Y et al., Passive repetitive stretching for a short duration within a week increases myogenic regulatory factors and myosin heavy chain mRNA in rats' skeletal muscles.
(11) Weppler and Magnusson, Increasing Muscle Extensibility: A Matter of Increasing Length or Modifying Sensation? http://ptjournal.apta.org/content/90/3/438.long