The Truth About Flexibility vs. Mobility By Brock Armstrong , Get-Fit Guy September 6, 2018 
Strength, power, endurance, and fat loss are the terms we hear the most when we talk about fitness, but there is an important term that we don't hear very often and that is mobility. Even when we do hear about it, it is often lumped in or confused with flexibility. To me that is like confusing your avocado with your toast. You can have one or the other but it is best to have a little of both.
What does that delicious metaphor mean exactly? I will tell you. But first, some definitions.
Flexibility is defined as the range of motion or degree of extension, in a joint or a group of joints, that its tissues are capable of. Mobility is defined as the ability for a body to perform functional movement patterns without restrictions in the range of motion (ROM).So, that means a flexible person may lack the core strength, balance, or coordination to perform the same functional movements as a person with greater mobility—but that same mobile person may not be able to bend themselves in half as easily. I am being glib (with apologies to my flexible friends) but that is often the case.
What Are Sarcomeres?
For most of our lives, we have been told if we are stiff, we need to stretch more. And while this is partly true, if we spend the remainder of the day sitting in a chair, at a desk, only standing up at lunch and quitting time, it doesn't matter how awesome our downward dog was at 6:00 am, we are going to be stiff, inflexible, and less than mobile. This is mostly due to a thing called a Sarcomere.
Sarcomeres, in an overly simplified nutshell, are the contractile units in our muscles. In essence, our muscles only move because sarcomeres produce the force required for us to move. When we are sitting at our desks all day our sarcomeres actually alter their shape on the cellular level. This is likely an evolutionary trait that makes it easier and easier for our bodies to do more and more of what we are already doing a lot of. Yep, you guessed it. That means that even if we do a killer 60-minute yoga session this morning, our sarcomeres will still choose the eight hours of sitting on our butts to adapt to rather than our Twisted Half Lizard.
But don't panic, we can rebuild this!
Body Movement Is Key
To undo the sitting stiffness, for example, we need to get up and move more frequently with more extended tissue length. Doing things like using a standing desk for part of the day, then get down and sit on the floor for a while, then squat for a bit, and walk around as much as possible between each position would be a good place to start. Also, choosing to avoid heeled shoes (most of the time) which have been shown to shorten tendon length, maintaining good long and tall posture, and even changing our sitting position frequently can help.
Eliminating that stiff feeling will not be achieved by stretching the crap out of your poor leg muscles, tendons and ligaments.
In other words, eliminating that stiff feeling will not be achieved by stretching the crap out of your poor leg muscles, tendons, and ligaments for thirty or even ninety seconds per day.
Remember that your sarcomeres naturally adapt to whatever length you would like by gradually loading your body in healthier ranges of movement. So, taking more opportunities for natural movement more frequently will help you develop mobility and maintain flexibility.
You can use strategies from the article How to Get More Flexible to increase your ability to move your joints through a range-of-motion (e.g. reaching your arms overhead while you're walking, getting your hips into a deep squat, lunging side to side while you are on the phone, etc.) but if you really need to increase the flexibility in the muscle itself, rather than simply increasing range-of-motion (or telling your sarcomeres to stop turning themselves into a chair), you are going to need to stretch for longer than you likely think.
Increase Flexibility
Do you truly need to increase flexibility in a muscle? If you have been neglecting your general movement long enough, you just might. If you do, you may be surprised to find out that research says that to truly optimize your muscle length, you must hold a stretch for three or more minutes!
A study looked into the Acute Effects of Different Stretching Durations on Passive Torque, Mobility, and Isometric Muscle Force in the hamstring muscle during a straight leg raise, and it compared stretching durations of 20, 60, 180, and 300 seconds. It was found that over 180 seconds of stretching was required to decrease muscle stiffness and to truly increase flexibility.
So although three minutes may seem like a long time, it can actually require a long stretch like that (such as you might experience during a yoga class) if your lack of flexibility is due to very tight muscles. And of course, as we found out earlier, that can all be undone if we don't also get the heck up out of our chair and move our bodies on a cellular level.
Mobility and Flexibility Tips
To finish off, here are four quick and dirty tips.
General daily movement is what determines our health, fitness, and mobility. Like I always say: exercise is for your bulging biceps, movement is for your good health. Forget about stretching tight body parts to make them looser. It is clear that we need to look at this with a longer lens. Extreme stretching in short intervals and occasionally during the week is fun, but if you want to truly stay mobile, focus on less extreme intermittent movement breaks instead. Remember that being bendy and flexy is not magically better for you. Having functional muscle and tendon length (long enough to achieve your movement goals) is all you need. In fact, being too flexible and stretchy can backfire on you.For more stretchy info, flexy tips, and to join the bendy conversation, head over to Facebook.com/GetFitGuy or twitter.com/getfitguy. Also don't forget to subscribe to the Get-Fit Guy podcast on Apple Podcasts, Stitcher, SoundCloud, Spotify, Google Play or via RSS.
