I was recently teaching a musician wellness class for a group of high schoolers (with a few college students/grownups mixed in), and the bulk of the girls were very hypermobile, especially in their knees and elbows. They were also, coincidentally very disembodied and disconnected from their body, as many teenagers (and people) can be. When I explained what hypermobility is, and how to tell if your knees are hypermobile, one girl immediately said "This is how I always stand (knees locked out beyond 180 degrees). Should I not do that anymore? It doesn't hurt." I in turn suggested that she not lock out her knees or elbows, but it reminded me of another side of hypermobility - that of pain, joint dysfunction, and potential damage to the surrounding tissues that may take years to manifest.
I've mentioned hypermobility before, but mostly in terms of fingers that won't behave in the context of music (piano, violin, clarinet, etc). Joint hypermobility syndrome is often characterized by many hypermobile joints, i.e. joints that move beyond normal range of motion. Yet, hypermobility is also a result of inherited (genetic) factors, lack of proprioception (knowledge of the where the body is in space), muscle weakness/strength imbalances, as well as all-over joint instability and susceptibility to soft tissue and joint injuries, as well as pain. It can also be part of a larger diagnosis, such as Ehler-danlos syndrome or Marfan syndrome, amongst others. (*Ehler-danlos syndrome is a connective tissue disorder than can manifest in many other non-hypermobile ways, including internal organ and skin dysfunction).
I recently read a very insightful blog in Yoga International, about a woman diagnosed with JHS, working with a wide range of symptoms including joint pain, excessive range of motion, immunity challenges, osteoarthritis, and a host of other health challenges. When someone who is hypermobile loads an unstable joint with weights or body weight, they are not using muscles to hold themselves up, but instead their ligaments are bearing the brunt of the job. Most hypermobile students do not need to stretch their ligaments, although the muscles themselves may be weak and at a shortened resting length. They often instead need to build strength and stability within a joint, rather than continually expanding range of motion. I myself am not particularly hypermobile, but I have seen excessive ranges of motion glorified in yoga, gymnastics, exercise, and other movement disciplines as a "goal." One thing to keep in mind is whether achieving a pose or movement is an aesthetic goal, or a movement goal. Dancers are often hyper mobile, and the attainment of a certain dance position is an aesthetic goal, despite how it affects the body long term, and that's a separate issue.
Some of my yoga teachers tell horrifying stories of debilitating pain after yoga classes in which they used their inherent joint instability to "achieve advanced poses" or perform impressive feats, only to regret it later. Even if you're not a yoga teacher or practitioner, it's important to be sensitive to the fact that most people who are hypermobile don't know that they are, and don't know that there's a potential for long term tissue damage and pain, even though pain may not manifest for years (or ever). As musicians, music instructors, and movement educators we have the ability to help our students find their natural joint ranges of motion, strengthen their tissues, and help them in their own journey of kinesthetic learning.