Stretching is known as a very efficient tool to increase flexibility. In fact, it is the most effective way to improve it, and flexibility is highly trainable. Unfortunately, this is not the only reason people stretch though.
Many people stretch prior to and/or after exercise, with the goal of either improving performance during a training session, reducing the risk of injury, or reducing muscle soreness after the session. However, when looking into the literature, surprisingly, there is no evidence confirming these are the case.
What the studies found:
The traditional thought is that stretching before exercise is crucial to avoid injuries. However, as opposed to what people think, recent research has reported stretching before exercise actually prejudices muscle performance (1).
Although warming up is essentail for injury prevention, stretching is not, for the surprise of many. Warm-up exercises are made to prepare the muscles for the exercise session, whatever the sport/modality is. Moves are generally the same as used in the modality, only made gently. That increases blood flow and body temperature, preparing the muscles and enhancing performance as a consequence, and also reducing the risk of injury and muscle soreness (2).
A recent review (3), which looked into the effects of stretching pre and post-exercise for prevention or treatment of delayed-onset muscle soreness (DOMS), reported very consistent findings among the included studies:
There was minimal to no effect on muscle soreness improvement after working out (between half a day and three days afterwards). It seems stretching before or after exercising is not useful if the goal is to reduce muscle soreness. This study did not look into the effects on performance though.
On top of not reducing DOMS, stretching also reduced performance. A recent meta-analysis (analyses of data from different studies about the same subject, used to identify the common effect among these studies) looked into the acute effects of pre-exercise static stretching. And they concluded that stretching during warm-up should be avoided as it has acute effects on maximum muscular strength as well as explosive muscular performance.
The authors add that if static stretching is to be done, the smallest negative effects were when stretch would last less than 45 seconds (4).
Another study (5) found that stretching before exercise reduced concentric and eccentric strength. And they also suggest caution when recommending dynamic instead of static, as the effects were found on both static and dynamic stretching.
It is then clear the importance to limit any type of stretching prior to exercising, as it affects muscle strength, and it does not prevent injuries.
However, it looks like stretching prior to / during exercise is not a complete waste of time: recent studies found that static stretching of the antagonist musculature would improve performance first, by increasing the neural drive to the agonist muscle, second, by decreasing neural drive to the antagonist muscle; and third, by reducing antagonist muscle stiffness and opposing forces or a combination of these factors (6).
So, if resistance training is your sport, antagonist stretching may be the one to go, as it may enhance strength performance and muscle activation of agonist's muscles, and as a consequence, increase the number of total reps. This stretching, however, should be applied inter-set rest period.
- For activities that require power, strength and endurance, it can reduce up to 7.5% of maximal force production.
- Increase in muscle fatigue (6).
- Reduction in muscular endurance.
- Detrimental to muscle strength and performance in running.
- Does not change the actual mechanical properties of muscle.
- No reduction in muscle soreness – but it may provide a transient relief of soreness/sense of well-being.
- To increase flexibility (done as flexibility training, in a different time than your normal training session), by increasing range of motion (ROM) if trained between 10-30sec, repeating 2-4x per exercise;
- Effective to improve muscle tightness;
- Rehabilitation (increases muscle length / ROM /align collagen fibres during the healing process);
- Chronic stretching programs = may improve performance/strength, but probably due to muscle hypertrophy, not stretching per se;
- Sports that need a high degree of flexibility should use short-duration static stretches with lower intensity stretches to minimise the possibilities of impairments (e.g. gymnastics, dance).
Depending what your reasons for stretching are you may benefit from doing it before/after exercise. To sum up, here is what the studies say when it comes to stretching:
- Increase flexibility – correct (flexibility is highly trainable).
- Enhance performance – not recommended: it actually acutely reduces performance (but it’s not as significant if the stretching is under 30 seconds).
- Prevent injuries – not recommended: no injury prevention is reported in the literature.
1. Miranda, Humberto, et al. "Acute effects of antagonist static stretching in the inter-set rest period on repetition performance and muscle activation." Research in Sports Medicine 23.1 (2015): 37-50.
2. Shellock, Frank G., and William E. Prentice. "Warming-up and stretching for improved physical performance and prevention of sports-related injuries." Sports medicine 2.4 (1985): 267-278.
3. Herbert, Robert D., Marcos de Noronha, and Steven J. Kamper. "Stretching to prevent or reduce muscle soreness after exercise." Cochrane Database of Systematic Reviews 7 (2011).
4. Simic, L., N. Sarabon, and Goran Markovic. "Does pre‐exercise static stretching inhibit maximal muscular performance? A meta‐analytical review." Scandinavian journal of medicine & science in sports 23.2 (2013): 131-148.
5. Costa, Pablo B., et al. "Effects of dynamic stretching on strength, muscle imbalance, and muscle activation." (2013).
6. Amiri-Khorasani, Mohammadtaghi, and Eleftherios Kellis. "Acute effects of different agonist and antagonist stretching arrangements on static and dynamic range of motion." Asian journal of sports medicine 6.4 (2015).
7. Trajano, G., et al. "Static stretching increases muscle fatigue during submaximal sustained isometric contractions." J Sports Med Phys Fitness 55.1-2 (2015): 43-50.