But we now understand that increasing our flexibility has much less to do with the physical length of our muscle tissue, and much more to do with the part of our body that controls and moves our muscles: the nervous system. Our brain and spinal cord, which make up our central nervous system (CNS), are constantly monitoring the state of our body. One of the main imperatives of the CNS to keep our body where it perceives it is safe. Normal movements that we make throughout our day are considered safe by the CNS because it knows and trusts them. But on the other hand, our CNS is not familiar with ranges of motion that we never move into, so it’s much less likely to consider those places safe. When we stretch, if we move into a place that the CNS isn’t familiar with, our nervous system will likely end our stretch by creating a sensation of discomfort at the end range of motion it considers safe.
For example, if you happen to work on your computer for 8 solid hours a day (and if you don’t take frequent intermittent stretch breaks for your shoulders - hint hint :) ), the CNS becomes very familiar with the arms-forward position that you use while typing and considers that range safe. Then later, if you decide to do a chest stretch in which you take your arm out to the side and then behind you, the CNS doesn’t feel that that movement is safe because you so rarely go there, so it will limit your range very early on in the stretch.
A major takeaway from this new flexibility paradigm is that when we increase our range of motion through stretching, it isn’t because we pulled on our tissues and made them longer. It’s because we visited the edge of our stretch (also called stretch “tolerance”) enough times that our CNS started to feel comfortable there and it began to allow us to move deeper into that range.
OKAY, I THINK I’M STARTING TO GET IT, BUT WHY IS THIS IMPORTANT?
It’s definitely interesting and more scientifically accurate to understand this previously-overlooked role that our nervous system plays in flexibility. But whether it’s your nervous system or the physical length of your muscles limiting you in a stretch, why does it matter? Isn’t a stretch a stretch, regardless of the mechanism behind it?