Stretching muscles is something that we often do without even thinking about it. You likely stretch a bit when you wake up in the morning or when you get up from sitting or standing in one position for a while. If you are involved in a sport, you might do specific stretches to help reduce tension or maintain range of motion in your body. But what happens, anatomically, when we stretch? In this article, we’ll look into what the research says about what might be happening in our body when we stretch. We’ll also take a look at why and how to stretch.

What is stretching?

Stretching, most generally, is lengthening muscles with the intention of increasing range of motion. More specifically, there are several common kinds of stretching. Static stretching is something most people are familiar with. This is the simplest version where you reach and hold a shape for a few breaths or more, then release.

There is also dynamic stretching, which describes stretching your muscle while moving. Another type is ballistic stretching, which involves adding a little bounce while trying to lengthen a muscle. And another type that has become more common is proprioceptive neuromuscular facilitation (PNF) technique. This type of stretching follows a protocol of alternating between stretching, then isometrically contracting the muscles against resistance for a few seconds, then stretching again. 

Mechanisms

The real answer to the question, what happens when we stretch muscles, is we don’t know. What’s most likely true is that we have more than one mechanism working together to create the end result of increased range of motion. Much of the research looking for mechanical changes from stretching has been inconclusive.

One review study reported that muscle length changed after short-term stretching protocols, but the change in muscle length was temporary (Holzman Weppler and Magnusson, 2010). Other research has suggested that the mechanisms of change in joint range of motion after we stretch are actually based on sensation tolerance happening in our nervous system (Freitas et al., 2018; Holzman Weppler and Magnusson, 2010; Ben and Harvey, 2010). It’s possible that as our tolerance to stretch sensation increases so does our available range of motion. 

Why stretch?

Regardless of how we do it, stretching is an effective way to increase range of motion. And maintaining a healthy range of motion is important for functional movement. If we do sports or athletic activities that build certain patterns of strength, maintaining a balance of flexibility is important for being able to access the strength that we have and for reducing the chances of injury.

If we sit a lot, at a desk, then we can benefit from stretching too. We can feel stiff as a result of both activity and inactivity. And, as we age, we all tend to get stiffer and dry out. Stretching can be helpful for ameliorating the effects of aging. We can’t avoid getting older, but we can do things like stretching to care for our bodies and slow the effects. A recent review study even found that stretching may have benefits for our cardiovascular system (Wong and Figueroa, 2019).

How to stretch?

Research suggests that all of the types of stretching effectively increase range of motion (Thomas et al., 2018). Some individual studies have found one particular type of stretching to be more effective than another type on a particular muscle group. For example, one review paper found that static stretching increased range of motion more than ballistic or PNF techniques (Thomas et al., 2018). But a different study found the opposite, that active stretching resulted in greater range of motion than static stretching (Meroni et al., 2010). So, it’s hard to generalize from these studies. It may be that different muscle groups respond differently to types of stretching. 

As far as the effectiveness of stretching on range of motion, frequency seems to matter more than the style or technique of stretching. A recent review paper reported that weekly frequency of stretching was positively related to range of motion (Thomas et al., 2018). As the frequency of weekly increased, the range of motion gains increased as well. They did not find a relationship between duration of an individual session of stretching and gains in range of motion (Thomas et al., 2018).

Conclusion

Stretching is something that usually feels good and is good for us! Regardless of which type of stretching we choose to do, it’s likely going to be effective at increasing our range of motion. And it may have other positive effects throughout our body. These are good reasons to add some stretching to your movement routine.

References

Ben, M. and L.A. Harvey, 2010. Regular stretch does not increase muscle extensibility: a randomized controlled trial. Scandinavian Journal of Medicine and Science in Sports. 20:136-144.

Freitas, S. R., B. Mendes, G. Le Sant, R.J. Andrade, A. Nordez, Z. Milanovic. 2018. Can chronic stretching change the muscle-tendon mechanical properties? A review. Journal of Medicine and Science in Sports. 28:794-806.

Holzman Weppler, C. and S.P. Magnusson. 2010. Increasing muscle extensibility: A matter of increasing length or modifying sensation? Physical Therapy. 90(3):438-449.

Meroni, R., C.G, Cerri, C. Lanzarini, G. Barindelli, G.D. Morte, V. Gessaga, G.C. Cesana, and G. de Vito. 2010. Comparison of active stretching technique and static stretching technique on hamstring flexibility. Clinical Journal of Sports Medicine. 20(1):8-14.

Thomas, E., A. Bianco, A. Paoli, A. Palma. 2018. The relation between stretching typology and stretching duration: The effects on range of motion. International Journal of Sports Medicine. 39:243-254.

Wong, A. and A. Figueroa. 2019. Effects of acute stretching exercise and training on heart rate variability: A review. Journal of Strength and Conditioning Research. 35(5):1459-1466.

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