Part 2 Mobility Vs. Flexibility: What’s the difference?

Recap:  Part 1 Mobility vs. Flexibility:  What’s the difference?

It’s difficult to talk muscles and mobility or flexibility without first considering a higher order: the nervous system. Without this system, much of our bodies’ communication and interaction with our outside world would be lost. Behind every muscle is a nerve. A neuron (nerve cell) and the corresponding muscle fibers that it innervates is called a motor unit. These are called units because when one neuron fires an impulse, it signals the muscle fibers connected to it to contract. Neurons within the hand do not innervate as many muscle fibers compared to neurons within our quadricep muscle (thigh) because hand movements are more fine-tuned and require a high degree of dexterity, precision, and accuracy.

Much of the above information is about our peripheral nervous system where our nerve terminals form neuromuscular junctions with our muscle fibers. However, the central nervous system (CNS) is the headquarters of the body because it consists of the brain and spinal cord. It’s quite difficult for parts of your body to function without it (fun fact: your gut can actually perform digestion well without your CNS – perhaps this is why it’s called “the second brain”). Our nervous system operates as a big interstate highway. It transports signals up into the spinal cord and then the brain, which then get processed and sent back out to the body to produce an action. For example, when your microwave timer goes off signaling that your food is done, you hear the beep which instinctively tells you to get up and go grab it. In other words, a stimulus (microwave beep) produces a response (walking to grab the food). Imagine this like an endless loop. This is how we interact with our environment every-day. Some loops are more reflexive and less voluntary. For instance, touching a hot stove that you may have thought was not hot results in you pulling your hand away before you even form the thought “*$#@! this is hot”. Or, remember when you went to the doctor’s office and s/he hit your knee with a hammer, that’s a reflex loop response! Here is the cool part – the body’s nervous system has a degree of control on conscious and unconscious muscle tension and reflexive contraction. It can be used to increase and decrease range of motion! Watch below for examples.

Try this: with your knees straight, bend down and see how far you can touch your toes by sliding your hands down your legs. Attempt to exhale your breath as you reach down. Once you feel like you can’t go any further without bending your knees, look to see how far you’re away from the floor or look to see where your hands touch on your legs. Now, lay on the floor and bend your knees like you’re about to do a sit up. Then, take 6 deep breaths in through your nose and out through your mouth. Try making your inhale 4 seconds long and your exhale 6 seconds long. Blow all of your air out to the point where you can’t talk anymore. You should feel your ribs depress down towards your feet, travel backwards towards the floor and slightly up towards your neck (like someone is giving you the Heimlich maneuver!). You may feel your abdominals contract as if you were wrapping yourself up in saran wrap. Try 2 sets of 6 deep breaths. After taking those 6 deep breaths, try bending over and touching your toes again. Did you get farther? If you didn’t get farther, did it feel smoother? Breathing is one of our primary links to help control our nervous system’s fight or flight response. That flight or fight response readies our body to deal with a stressor. Stressors come in all different shapes and sizes. They can be physical, emotional, or psychological to name a few. A stressor for one person may not ignite the same response in another person. Like the above videos showed, the body can deal with a “threatening” (i.e. 5-star slap on the back, rubbing something hard on your jaw etc) stimulus by relaxing muscle tone or creating global muscular tension. At times, muscle tension stays in a place as a protective mechanism because the body may believe it’s safer that way. Or, perhaps the body creates tension somewhere because it doesn’t feel safe to get into that position. For example, if you can’t bend down and touch your toes in standing, but you can while side-lying or sitting, range of motion may not be just the one to blame. It may be how you interact with gravity when standing or sitting.

Influencing our nervous system is more beneficial than trying to change muscle structure itself.  Common narratives surrounding “mobility” tools such as foam rolling, lacrosse ball smashing, or instrumented soft tissue mobilization (ISTM) often dictate that we are trying to break up scar tissue or muscle adhesions. I’d challenge that our tissues are a bit more resilient than that. Why would it be that we can roll on a foam roller and “break up tissue”, but squatting 400 lbs doesn’t melt our tissues away? I’d wager that it’s very difficult for human hands or other “mobility” instruments to produce enough pressure to change muscle tissue. So then how do these (foam roll, lacrosse ball, ISTM) mobility instruments work? Well, we tap into our neurological system by giving ourselves a dose of pressure. We’re able to sense how much pressure we’re putting on that body segment because we have receptors in the skin surrounding the involved muscle that provide this information. This sensation may even feel pleasurable. When we sense the pressure we’re putting on our body segment, it turns into a signal that’s processed by our body. This signal can override other sensations that we may feel depending on the properties of the nerves that are stimulated. This is one of the factors that goes into why foam rolling a painful, overworked, or “tight” body segment feels better after. Other ways to influence the nervous system is to experience heat or cold, slow/deep breathing, vibration, performing exercise, moving, or stretching. All of these have impacts on our system, which may result in increased range of motion. But, how do we keep our range of motion? If we all of a sudden have this new range, will it go back to the way it was within 10 minutes? 30? 5 hours? Good question – we do not have the exact answer to how long it may last. However, we do know that if you consistently find ways to gain even inches in motion that are required for the tasks you want to complete and then consistently use that range actively, your system will adapt to this new range. As the saying goes “use it or lose it”.

To recap, here is a summary: influencing the nervous system through pressure, heat, cold, exercise, smelling, hearing, vibration, breathing, massage etc. could provide a window of opportunity for increased range of motion. Once the window is open, adding some degree of load (putting force into an object or resist the force put on you from an object) in the degree of range that was “newly created”. Adding load results in muscle contractions. The nerves behind those muscles are paving new pathways or roads.  The more you travel the road, the more permanent the road becomes.  So create new roads, travel them consistently, and continue to explore new motions of the body.

By:  Henry Mercier, MS, ATC

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