Weekly musings, 5/20/18: the shoulder, proprioception, and co-contraction
During a webinar I hosted recently, an attendee wrote afterwards and asked me to further explain why proprioception seems to be diminished in people with hyper mobility. (Hyper mobility refers to the ability to move the joints in extreme ranges of motion. One of the causes is ligaments, which provide stability to joints, are stretched, potentially leaving the individual with a sense of instability). Research shows a correlation between hyper mobility and poor sense of where your body is located in space, but the reasons why that occurs isn’t fully understood.
A paper by Scott Lephart and Rajesh Jari* suggests the ligamentous structures of the shoulder may provide sensory feedback to the brain about joint position, which causes a reflexive contraction of the muscles that stabilize the shoulder. Proprioception, or accurate sense of joint position, is required for the brain to tell the muscles to contract- it’s a feedback loop.
When you take hold of something heavy, like a kettlebell, barbell, or suitcase, before you grasp the item, the brain is figuring out how much strength you need to hold on to the weight. Otherwise, the shoulder wouldn’t stay in place- the weight would pull the arm down out of the shoulder socket. I wonder if strength training tunes the feedback mechanism, making the output a little more accurate based on the input? Regardless, strength matters and having a sense of stability can make many things in life a little bit easier.