Why do we stretch?

Stretching is well known about and used worldwide. An international survey revealed 53% of physically active adults normally stretch and 80% of personal trainers in the United States prescribe it (Nuzzo 2019). We may stretch because we have been advised by a medical professional, or because it just seems like the right thing to do. But why do we actually do it?

Stretching can be seen as an innate behaviour, as observed by cats after waking from a long sleep. It is also instinctive in humans to yawn and stretch after waking, even babies do it. This is known as pandiculation (Warren 2019). A lot of animals do this (30-40 times per day) to prepare their body for activity (Essential Somatics 2015).

Pandiculation is our innate response to the sensations of lack of movement and to tension building up in our muscles. The science behind it is that it reverses the muscular-atonia of the REM-sleep (Walusinski 2006). It is also supposed to improve blood flow and reduce stress, by activating the parasympathetic nervous system. The yawn increases oxygen intake into the lungs, while the muscle lengthening increases the heart rate through activating muscles and encouraging blood flow to extremities (Farinatti et al 2011).

Pandiculation is however different to static stretching. When you pandiculate, you are contracting your muscles in order to lengthen them and reach the end of its range (Essential Somatics 2015). The “cat stretch” often performed in pilates is actually based on a cat eccentrically lengthening its back muscles.

Passive stretching involves holding a muscle in its lengthened position using external force – a partner, object or another limb. Despite the name, it is actually not entirely passive due to the small force applied to the muscle (De Deyne 2001).

So have we got it all wrong? If animals eccentrically contract their muscles to regain their length, why are we trying to passively stretch them?

Stretching was first recognised in an osteological study in the 18^th century, however it can be dated back to the Hippocratic era (460 BCE) when the roman empire would use it to keep their gladiators in shape (Tipton 2014).

Hippocrates was the first recorded physician to prescribe a written exercise programme (Tipton 2014). He believed that it was possible to have a stronger and more rested body after exercise, through walking (hence why we now cool-down after exercise), baths, massage and stretching (Redman 1846). A lot of his advice is still used today, however these were based on theory which in the modern day, would be at the bottom of the hierarchy of evidence. 

Stretching generally focuses on increasing the length of a musculotendinous unit, in essence increasing the distance between two joints and holding for an extended period (Brukner and Khan 2017). The prior belief was that the prolonged tension applied by a stretch on a muscle overcomes the force of connective tissue in order to increase the length (Roberts 1995). Imagine stretching out some plasticine and seeing how it holds its new elongated shape.

Other studies contradicted this. Crawford (1973) found that when immobilising the muscle of young rabbit in the extended position, there was actually a reduction in sarcomere addition. The muscle belly of the immobilised limb was actually shorter after the trial and it was in fact the lengthening of tendon that resulted in the increased range. This indicated the importance of movement in stimulating normal growth. The increase in tendon length has been suggested to be due to the isometric contractions of the rabbit trying to move when immobilised.

Williams and Goldspink (1978) then found that an increase in skeletal muscle length has been shown to result from the serial addition of sarcomeres. This was measured in both the postnatal development of mice and adult mice. This increase in sarcomeres is referred to as sarcomerogenesis and will be discussed in my next blog.

The limitations to these studies are that they both used animals and also involved a very long period of immobilization. As far as I know, no physio is recommending to patients to splint their muscles for a few months in order to improve flexibility.

More recent research shows that the reason the muscles extensibility improves through stretching is that the stretch tolerance of the muscles improves. This is by habituation of the protective stretch reflex to the stretching sensation (Weppler and Magnusson 2010). This would suggest that stretching does have a positive effect on flexibility and has been consistently proven to do so (Apostolopoulos et al 2015).

The current recommendation for stretching is for a slow, sustained stretch of at least 10-15 seconds. The intensity, duration and frequency should increase as flexibility improves and it should also be pain-free (Bruckner and Khan 2017). Many studies have looked at the frequency of stretching required in order to significantly improve range of motion. The most beneficial effects appear to be when performing them at least 3xper week (Apostolopoulos et al 2015).

Stretching has also been thought to be beneficial for injury prevention and improving performance (Hartig and Henderson 1999). Again though, more recent evidence suggests that this is not always the case. Research consistently found a reduction in power immediately after static stretching (Behm and Chaouachi 2011). This prompted the shift for more dynamic stretching to be performed prior to exercise.

Lauersen et al (2014) performed a systematic review looking at the effectiveness of exercise interventions at preventing sports injuries. Strength training had a significant effect in reducing injuries however stretching had no beneficial effect. It is however important to point out that the systematic review only included two studies on army recruits and one internet-based study on the general population for stretching. Therefore, we should tread carefully when applying this information for all sports, such as dance and contortion where flexibility may be deemed more important.

The current recommendation based on the evidence is therefore that stretches can be used to improve flexibility, but are there more effective ways to achieve this? The next post will look at alternative methods to decipher what is most effective.

References

Apostolopoulos, N et al (2015). The relevance of stretch intensity and position – a systematic review. Frontiers in Psychology, [online] 6, page 1128. Available at https://www.frontiersin.org/articles/10.3389/fpsyg.2015.01128/full#h1. [Accessed 24th November 2019].

Behm, D and Chaouachi, A (2011). A review of the acute effects of static and dynamic stretching on performance. Applied Physiology, [online] 111 (11), pages 2633-2651. Available at https://link.springer.com/article/10.1007%2Fs00421-011-1879-2#citeas [accessed 24^th November 2019].

Crawford, G (1973). The growth of striated muscle immobilized in extension. Journal of anatomy, 114 (2), pages 165-183.

De Deyne, P (2001). Application of passive stretch and its implications on muscle fibres. Physical Therapy, [online] 81 (2), pages 819-827. Available at: https://www.ncbi.nlm.nih.gov/pubmed/11175679 [accessed 15th November 2019].

Essential Somatics (2015). Pandiculation, the safe alternative to stretching. [online] Available at https://essentialsomatics.com/clinical-somatics-articles-case-studies/pandiculation-safe-alternative-stretching [accessed 23rd November 2019].

Farinatti, P et al (2011). Acute effects of stretching exercise on the heart rate variability in subjects with low flexibility levels. Journal of strength and conditioning research, [online] 25 (6), pages 1579-1585. Available at https://insights.ovid.com/crossref?an=00124278-201106000-00014 [accessed 22^nd November 2019).

Hartig, D and Henderson, J.  Increasing hamstrings flexibility decreases lower extremity overuse injuries in Military Basic Trainees. American Journal of Sports Medicine, [online] 27 (2), pages 173–176. Available at https://journals.sagepub.com/doi/abs/10.1177/03635465990270021001 [accessed 20^th November 2019].

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Nuzzo, J (2019). The Case for Retiring Flexibility as a Major Component of Physical Fitness. Sports medicine, [online] 50, pages 1-18. Available at: https://link.springer.com/article/10.1007/s40279-019-01248-w [accessed 12th December 2019].

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Weppler, C and Magnusson, P (2010). Increasing muscle extensibility: a matter of increasing length or modifying sensation. Physical Therapy, [online] 90 (3), pages 438-449. Available at https://academic.oup.com/ptj/article/90/3/438/2737895 [accessed 23rd November 2019].

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