The World of Stretching – Flexibility vs. Mobility

Lesson 1: Flexibility VS. Mobility

The terms “flexibility” and “mobility” are commonly used interchangeably in the English language, however; when you look at the definitions of each of these words their differences become clear.

Flexibility – implies a passive range of motion (ROM). This means having a practitioner or an external load move a joint or series of joints into a position. Flexibility is improved upon by multiple forms of stretching which can include, static, active isolated, dynamic, ballistic, and PNF. The most effective of these at improving flexibility are considered to be PNF and static stretching, the main topics of this course.

Mobility – implies an active ROM. This is a measure of how far a person can move a joint or a series of joints under their own power with their own muscles. Mobility can be improved upon by practicing mobility drills, static, active isolated, dynamic, ballistic, and PNF stretching. The most effective at increasing mobility would be considered to be mobility drills, and the more dynamic forms of stretching.

It is generally accepted that someone with good flexibility will also have good mobility and vice versa. Improvements in one will generally lead to improvements in the other. This may be one of the reasons why these words are used interchangeably in the English language.

Restrictions in ROM can come from a number of different areas. Firstly, and the one people think of most often, is a tightness in the tissues resulting in a limited ROM. A good example of this is in the hamstrings. When supine with the knee straight, flexing the hip will result in a stretch of the hamstrings. Eventually the sensation of stretching behind the knee in the hamstring tendons will be overwhelming resulting in the end of the available ROM. This is associated with a soft end feel. It is called a soft end feel because there is not an abrupt stop at the end of the ROM. You can feel more and more resistance build up as you get closer and closer to the end of the ROM. A hard end feel, or a bony block, can be felt when fully straightening the knee or elbow. When the knee/elbow locks out there is a bony block preventing further motion abruptly. Another end feel to be aware of is soft tissue approximation. This can be seen when fully bending the knee and the belly of the calves are being pressed into the posterior thigh. This feels similar to a soft end feel but it has its subtle differences. On yourself or with a partner, try to feel these different end feels. It is important that you can determine the end feel on all types of joints. Anything outside of what you are expecting for that joint may require medical referral before it is safe to practice stretching on that joint.

Restrictions in ROM can also come from a lack of accessory movements. Typically, this is witnessed following cast removal. The joint and surrounding joints become stiff after being fixed in place for so long. The ligaments and muscles tighten and atrophy. In this case joint mobilizations (not manipulations) may be more beneficial at first in improving the client’s function and ROM. On this point I would like to dispel some common misconceptions about flexibility and exercise. Exercise does not cause muscles to become tight. People who live a sedentary lifestyle are at greater risk of developing chronically tight muscles. During exercise muscles are moved through their available ROM, keeping them accustomed to their limits in ROM. Someone who lives a sedentary lifestyle may never expose the muscles to their limits in ROM leading to the muscles adaptively shortening. Furthermore, movement helps to lubricate the joints with synovial fluid, nourish the cartilage within the joints, and prevent adhesions from forming in the muscle and fascia. Does this mean if you exercise you don’t have to stretch? No, of course not. Almost everyone needs to stretch, but it is not the exercise that is forcing you to stretch. It’s the sedentary lifestyle to blame for that one.

Restrictions can also occur as a result of the fascia. Thickening or hardening of the fascia and fascial adhesions can all become painful and restricting. For the purpose of this class we will refer to the restrictions coming from muscular tightness, however; whenever a muscle is being stretched, the fascia is also being placed under tension. You cannot stretch one without the other.

Prior to moving into the next section there are two more terms I want to briefly discuss:

Elasticity – think of a rubber band, how when you stretch it and let go it will return to its original shape. Your muscles are highly elastic, and this is what allows us to move so efficiently.

Plasticity – this is the ability of an object (or in this case our muscles) to maintain some of the displacement achieved by stretching. A good example of this is a paperclip. When you unravel a paperclip it never quite returns to its same original shape.

This is important because the muscles are so elastic that any length increases achieved in stretching are quickly reverted to the original resting length. So then how can we permanently increase the length of the tissues? Consistency over time is the key. Generally, muscles will only maintain about 5% of the increases in length after about 10 minutes. So, stacking those 5% increases multiple times throughout the day, several times throughout the week, is the key to increasing the length of the muscles and tendons.

Some level of discomfort must be reached when we stretch with the intention of improving ROM. We can see from this graph displaying stress on the Y axis and Strain on the X axis that if the intensity of the stretch is too low only elastic changes will occur, meaning no permanent increases in ROM. However, if we raise the intensity of the stretch, we will enter the plastic deformation region and the muscles will maintain some of the increases in ROM. But its not that simple. In order for changes to be maintained the tissues need to be held in this state for a longer period of time, which is about 30 seconds depending on the clients age. We can also see with this graph that if we go too far damage can occur. This is easily avoidable by keeping a close eye on you client for signs of pain which could include wincing or pulling away from you. Always keep communication open. If the client feels any pain, they should be comfortable enough to tell you to stop. Remember to instruct the client that we want them to feel slight discomfort associated with stretching and nothing else, nothing more. It is partly up to the client to inform you when they have reached that point.

Similar to strength increases early in the program for an individual new to training, most of the improvements in ROM early on come from the nervous system. Rather than increasing the length of the tissues, the nervous system is learning that the body can handle more ROM than it originally allowed. In other words, your tolerance to the discomfort of stretching increases. Like pain tolerance, your stretch tolerance increases, and unlocks new degrees of flexibility you would have been able to achieve had the nervous system been removed from the equation.