Why are we talking about mobility so much lately? Some people lump it in with stretching/flexibility, or think it is stretching. That is only part of the equation. First let’s define flexibility, the ability to have an outside force applied to a part of your body and that force moves your body part into a position where you feel a stretch of your muscles. This is what we call a passive stretch. Whereas mobility is your ability to control and move your body/joints through a certain range of motion with strength, thus an active movement. In most cases we have more flexibility than we have mobility. Meaning we can be passively moved into a deeper range of motion than what we can control actively.
Why do we stretch?
Most people believe it is to become more flexible. That depends on the reason you are stretching, and the process you are using. When done with mobility principles, stretching can change muscle length, joint strength and control, and neurologic control. When done with dynamic stretching principles, it can help prep the muscles for the activity you are about to take part in.
The Science
For quite some time stretches have been given on a basis of time, from 10-30 seconds. When we are talking mobility those stretches are going to need to be held much longer, up to 2 minutes. In general a stretch is going to activate either the muscle spindle or golgi tendon units. Wait what? I know science terms. I’ll explain. The muscle spindle is within the muscle belly and sends signals to the brain about the length and changes in the length of a muscle. The Golgi tendon organ (GTO) is in the muscle-tendon junction and signals the amount of force being applied to a muscle back to the brain.
When a muscle is rapidly stretched, the muscle spindle signals its muscle to contract to prevent it from going too far, too quickly. Ultimately, the muscle spindle functions to alert the brain that nearby joints and soft tissues are in danger of being stretched too far. These are important concepts in understanding body awareness (also known as proprioception and kinesthetic awareness).
GTOs sense muscular tension within muscles when they contract or are stretched. When the GTO is activated during stretching, it inhibits muscle spindle activity within the working muscle so a deeper stretch can be achieved. GTOs are sensitive to changes in tension and rate of tension and, because they are located in the musculotendinous junctions, they are responsible for sending information to the brain as soon as they sense an overload. Static stretching is one example of how muscle tension signals a GTO response. So, when you hold a low-force stretch for more than ten seconds, the increase in muscle tension activates the GTO, which temporarily inhibits muscle spindle activity thus reducing tension in the muscle, and allows for further stretching.
The Science Applied
Whew, we got through that. Now when we apply a stretch to a muscle, the first thing that happens is the muscle spindle reacts to the lengthening of the muscle and may cause a muscle contraction is the movement is too fast of too much pressure, once the stretch has been held for more than 10 or so seconds the GTO kicks in, relaxes the reflex muscle contraction and allows you to feel the muscle being stretched. This does not change the length of your muscle though. This only calms the nervous system to allow the muscle to relax, or a contract if you apply more force. These short stretch relaxes can help to calm the system down before starting an exercise program, but again do not change the length of the muscle or its firing pattern.
Now that we understand that stretching affects muscle control and allows you to start exercising without causing injury. Now let's talk about mobility. Again this is your controlled range of motion. In order to create more range of motion that you can control, those stretches need to be held for a much longer time, and be accompanied by active muscle contractions and passive muscle stretching. Some people have heard of Proprioceptive Neuromuscular Facilitation. This is where the concept started. Over the last decade however, research has dove deeper and found that in order to make change to the muscle length you must hold the stretch for 2 minutes.
Mobility and Functional Range Conditioning (FRC)
The principles of FRC are based on creating not only better flexibility, but also strength through that new range of motion. It does this by focussing on joint function. We start by assessing the joint's ability to be moved (flexibility), then compare it to the joint's active range of motion (mobility), then compare that to the requirements for the sport or activity you are looking to participate in.
Example of Mobility
Let's use the example of hip flexion in cycling. Cyclists need a significant amount of hip flexion in order to achieve the proper cycling motion without causing movement of the hips on the saddle. When we look at a hip joint the primary movement is rotation. Wait what you just said we were looking at hip flexion. Yes, but in order for a hip to be able to flex properly, it MUST be able to rotate to allow flexion and even extension to happen. In FRC we look to see if there is abnormal hip rotation and we address that FIRST. Once we have determined what the hip needs, we then work it. You can see in this video that working the mobility of hip rotation is a several minute process, but one that results both in increased joint range of motion and also your ability to create force, aka strength, at that new range.
The amazing part of working mobility is that it also includes working your strength without the need for weights. You get to use your body's internal resistance to help build strength in your joints. The hip rotation is just one example of how to work hip mobility. Everyone’s needs are different and each person may need a different set up for this particular hip mobility exercise.
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