Last updated: March 20, 2020
An example of this concern is
It does not make sense to try to stretch ligaments! It is an unscientific, unsound, and bad idea. Muscles can stretch 200% but ligaments only 10%. Beyond 10% they are damaged.
You can replace the word “ligament” with the fascial tissue of your choice: “joint,” “tendon,” etc. A more complete response to this type of concern can be found in the article on Yoga International called “It’s okay to stretch your ligaments.” Below is a brief summary of some of the key points (the full article has footnotes with references to the source of the statistics cited):
Not only do our ligaments, tendons and fascia stretch, they are supposed to stretch. They are naturally elastic: more so than our muscles! Elasticity is not how stretchy something is but rather it is “the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed.” Think of a spring: you can stretch it, which takes energy, but when you let go that energy returns as the spring shortens again. Stiffer springs are more elastic but less stretchy than weaker (more compliant) springs. Our ligaments are like stiff springs; our muscles are much more compliant. In fact, our muscles do not “snap back” after being stretched but have to engage to become shorter again. In this way, our muscles are not elastic at all, just stretchable like plasticine. Our ligaments, tendons, joint capsules, etc. are elastic and springy. It takes no energy for a ligament to return to its original length, but rather it returns energy to the body. This is exactly how springs work.
Humans are the running, jumping and bouncing primates: our hamstrings are more like hamsprings! Our fascia is different from that of our simian cousins—we bounce. Our Achilles tendon, for example, evolved to be longer, stiffer and springier than in other apes. It can stretch; and when that stress is released, the Achilles tendon snaps back like a tight spring, helping us to run and jump. Said another way, the highly elastic nature of many fascial tissues like tendons and ligaments allows us to walk, run, jump, and even throw with great facility and energy efficiency. This would not be possible if our ligaments and tendons were not able to stretch.
Human fascia has evolved to stretch and elastically recoil. How much a tendon or ligament can stretch before being damaged is quite variable: it depends upon where it is, and whom we are examining. One common statistic that is often cited is that a tendon can only stretch 8%~10% before becoming damaged. However, that statistic is an average derived from studies of very small numbers of people. Athletes’ Achilles tendons can elongate anywhere from a low of 6% (in some runners) to a high of 19% (in some swimmers). Even in a non-athletic population the range of Achilles tendon elongation varies from 5% to 13%. Some ligaments are superstars at stretching! The ligamentum flavum along the spine can stretch 80% without damage! Recently, even the very stiff iliotibial band has been found to be elastic: it stretches about 1~3 cm when running. It acts like a very stiff spring that helps to bring the back leg forward when we walk or run. All this just proves that fascial tissues, including our ligaments and tendons do, indeed, stretch. This is normal, healthy and necessary.
If we avoid stressing tissues, we invite atrophy—a slow steady decay of the tissue’s abilities. This happens to any tissue we avoid exercising including our fascia. Laurence Dahners, Professor (Emeritus) of Orthopaedic Surgery, noted, “A common clinical finding is that unloaded ligaments not only atrophy, but also undergo contracture.”[1] In other words, if we are not stressing our ligaments, our joints tighten up and we lose range of motion.
Beyond the points made in the above article are the thoughts of a well-known and respected physical therapist and teacher, Greg Lehman. It is Greg’s considered opinion that stressing fascial tissues like ligaments and joints can only make them thicker and stronger. Through the process of adaptation, the tissues we stress become stronger, so directly targeting the ligaments will not “over-stretch” them, which seems to be the fear, but will rather thicken them and make them less likely to over-stretch. Here is a quote from Greg:
Don’t you find it odd that [those who criticize stretching ligaments are] pretty adamant that you can’t change muscle length with stretching but the same stretching will increase the length of a ligament? We actually have no evidence that a ligament gets longer with stretching. We see the same thing with long term stretching and tendons. And tendons are similar to ligaments in how they respond to load. … When you look at tendon and ligament biomechanics research we see that ligaments are incredibly slow to adapt. And that tensile load, if anything, makes them stiffer and stronger. There is no other load that you can put on ligament. If you pull it/tension it, it responds by getting stronger. (Check these studies here, here and here.)[2]
In short: Our fascial tissues are designed to both restrain too much movement but also facilitate movement. They are elastic: they build up internal tension when stretched and can release that energy back into strong, quick movements in the opposite direction. These fascial tissues include our tendons and ligaments,[3] which are in series with our muscles, as well as the layers of fascia parallel to our muscles, surrounding and investing them. Even one of the strongest, stiffest pieces of fascia in our body, the iliotibial band, is elastic. Like other fascia, it is designed to stretch and that is a good thing.
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1 Laurence Dahners, Laury Dahners’ Orthopedic Page (accessed January 10, 2020). https://laury.dahners.com/assets/documents/orthopedic/KD%20paper%20for%20web%202020.pdf
2 Greg Lehman, “If you want to stretch your hamstrings please continue to do so.” Reconciling Biomechanics with Pain Science (2012).
3 The fact that ligaments are in series with the muscles is a newer realization. Most textbooks still show the ligaments being in parallel to the muscles; however, the work of Jaap van der Wal sheds new light on this old model. See Jaap van der Wal, “The architecture of the connective tissue in the musculoskeletal system,” International Journal of Therapeutic Massage and Bodywork 2.4 (2009): 9–23.