If we think of a new movement sequence as a piece of code that is stored in the brain. That code would be a list of instructions.
Contract muscle A, relax, B stabilise with isometric contractions in C and D, then.......(I know, oversimplification but I am sure you get the idea!)
Each new experience is stored as yet another piece of code. Lots of stored sequences is like a huge library of movement information that we can draw on.
Lots of new, ever changing and challenging experiences will result in a lot of learned sequences. This is healthy it helps us cope with our changing environment. It helps us react to danger and cope with the changing demands of workload. Our body, effectively, has lots of movement tools to draw on. Muscles would be able to work with, and cross reference, all the other groups of muscles and movement sequences to ensure maximum efficiency of movement. This movement intelligence limits the likelihood of injury as we would then have the ability to access from our library, so many different sequences to ensure we move efficiently and healthily.

The word cross training used to refer to the idea of doing a very different and challenging type of movement routine to restore balance and add to movement intelligence. It now refers to a sport that does exactly the opposite, it hones a very limited skilled set of exercises. Ironically cross fitters now need to spend time cross training.
If you want structural body health, do something different. Really 'cross train'! Learn a new skill, get your body out of its comfort zone, challenge yourself and add to that movement library. It can be learning to juggle, climb, dance, yoga. Do it but don't over do it. Move on and gather movement intelligence.
Use this challenge technique to keep yourself generally healthy and also to restore healthy balance to your body if you sport or activity demand repetitive movement training.
Our Back in the Game class uses elements of parkour, (you couldn't get a more randomly challenging activity than that) to help people, including regular gym goers, to regain healthy movement. We have just started a new group,Wednesdays at 7am (yes am) for a lovely crowd from the older generation. I am so looking forward to witnessing their movement regeneration.
If you'd like to learn more about healthy movement and clever simple ways to achieve it. We run an Access to Movement Workshop. The next is on March 11th