Contrary to popular belief, the terms mobility and flexibility are not synonymous. They are actually distinct in both definition and their influence on performance. Flexibility is the term with which most people are familiar and often incorrectly use to describe mobility. Mobility is growing in recognition and can be divided further into active and passive. The distinction between these terms is critical for training because traditional stretches are not just ineffective, but can actually increase injury risk and hinder performance. The goal of this article is to clearly define each of these terms, briefly outline training parameters, and explain their relationship to physical health.
- Flexibility – the capacity of a given muscle or muscle group to stretch/lengthen.
- Flexibility focuses solely on the lengthening muscle, with no consideration to whether the motion occurs actively or passively.
- Passive Mobility – the range of motion available in a particular direction at a given joint or body region.
- Passive Mobility is created by an external force, not by your own muscles.
- Active Mobility – the range of motion that you can actively access at a given joint or body region.
- Active Mobility depends entirely on your own muscle contractions with no external force contribution.
So, flexibility and passive mobility are similar in that they both measure overall motion rather than focusing on active motion. Because passive mobility measures the motion available to a given joint or body region, it naturally requires adequate flexibility in the involved musculature as well. You can think of Active Mobility as the portion of Passive Mobility that you are able to access and use. Passive Mobility is almost always greater than Active Mobility. Sometimes the two are essentially equal, but Active Mobility can never be greater than Passive Mobility. Active Mobility is the most important of these three characteristics when it comes to physical health and athletic performance.
Passive Mobility represents the overall capacity for motion, while Active Mobility is the portion of that capacity that can be accessed and controlled.
What Determines Flexibility and Mobility?
Flexibility is fairly simple – it is the ability of a muscle or muscle group to lengthen. You can think of this like a rubber band. It is able to stretch a certain amount and return to its original length. This technically does not account for the effects of joint structure on motion. It does, however, depend largely on the influence of the nervous system – more on this later.
Passive Mobility is partially determined by flexibility, but also takes into account joint structure and the other surrounding tissues. This term is a more complete measure of the motion attainable at a given joint or body region when acted upon by an external force.
Active Mobility encompasses all the factors contributing to both flexibility and passive mobility. Furthermore, it layers the complexity of muscle activation, coordination, and strength.
It’s (Partially) in Your Head
When discussing flexibility above, I mentioned the important influence of the nervous system. This can sometimes be a difficult concept to wrap your head around, but bear with me. All perceived sensations are produced by your brain. The experiences of pain, touch, smell, sight, and hearing are all produced by your brain based on input from sensory receptors in your body. These sensations are intended to inform you about what is happening in your surroundings or inside your body. They typically do an excellent job of this, but can also sometimes be misleading. This is true with chronic pain (future article coming), just as it often is with the feeling of muscle “tightness”.
Why does your nervous system produce a feeling of tightness even when true muscle length is not limited? Largely as a protective mechanism. If your nervous system senses movement beyond the range that it deems as safe, it will produce a sensation of tightness to stop you from moving further. This most frequently results from a lack of control, coordination, and strength in that range. Thus, though seemingly counterintuitive at first, the fastest way to build lasting mobility is through targeted strength training rather than traditional stretching.
How do Flexibility and Mobility Relate to Athletic Performance?
With athletic performance, active mobility is king. This is because athletes rely on their ability to move actively to excel in their sport.
Imagine two dancers, A and B.
Dancer A is more flexible, with 130° of passive hip flexion mobility. However, because of limited active mobility, she is able to access and control only 90° of her available range.
Dancer B is less flexible and has only 115° of passive hip flexion mobility. However, dancer B has excellent active control over her range and is able to access 110° of her available motion.
Thus, dancer B will be able to actively raise her leg much higher (110°) than dancer A (90°). This advantage in active mobility will allow dancer B to achieve positions and maneuvers that are impossible for dancer A. Furthermore, because dancer A has 40° of passive hip flexion mobility that she is unable to access and control, she is more susceptible to injury. More is not always better when it comes to mobility and flexibility.
To summarize, active mobility is paramount for performance because this is the motion that the athlete is able to actually use in his/her sport.
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How do Flexibility and Mobility Relate to Injury Risk?
There is a lot of conflicting information going around about flexibility, mobility, and injury. Should you do dynamic stretches or static? How do flexibility and mobility relate to the risk of injury? Is stretching before or after a workout good or bad?
Dynamic vs. Static Stretching
Traditional static stretches – where you hold a stretch passively with no muscle contraction – can, temporarily, increase passive mobility and flexibility. Increasing passive mobility and flexibility is not inherently bad, but to be truly useful this increase must be combined with gains in active mobility. Without simultaneously building active mobility, you are simply adding more motion that is not actually accessible during movement. Traditional dynamic stretches such as leg swings are great as part of a warm-up to improve blood flow, but will not bring about large gains in either mobility or flexibility. So what should you do if traditional static and dynamic stretches both fail to effectively build active mobility? Don’t worry, in the next section I will teach you another way of training mobility that makes static stretching obsolete.
Mobility, Flexibility, and Injury
The most important factor in injury risk reduction is a combination of strength and control throughout an individual’s available range of motion – active mobility. When there is a large gap between active and passive mobility (as in the case of Dancer A), too much of the passive range is not accessible, usable motion. This translates to increased injury risk during athletic activity. While competing or training, athletes may be forced into the extremes of their range, so it is crucial that they have strength and control through as much of their range as possible. Put differently, when pushed past the limits of active mobility, the load placed upon the body may exceed the individual’s capacity to control that load. When stress exceeds capacity, injury typically occurs.
Focusing on reducing the risk of injury, it is not the absolute amount of passive or active mobility that is most important, but the ratio between the two.
When to Stretch
From the previous discussion, we know that traditional static stretches can actually increase injury risk by widening the gap between active and passive mobility. So, in the case of traditional static stretches, the answer is neither. I recommend avoiding these types of stretches altogether in the vast majority of cases. Traditional dynamic stretches can be a great addition to a warm-up and are also fine to include as part of cool-down. I will explain another mobility training method in the next section that improves passive mobility, active mobility, and flexibility simultaneously. This type of mobility work can be safely performed both before and after activity as long as it is properly prescribed and dosed.
To summarize, use dynamic stretches in your warm-up or cool-down, avoid static stretches, and train active mobility to realize true performance gains.
How to Train Active Mobility
Now that you understand active mobility, passive mobility, and flexibility; let’s discuss how to train. One of the best systems for training mobility is Functional Range Conditioning (FRC). FRC was developed by Dr. Andreo Spina and combines a deep understanding of anatomy with a focus on practical application. This system is just as effective for daily life and overall movement health as it is for athletic performance. You can learn more about the specifics of FRC here.
For the purposes of this article, I want to focus on just one part of the FRC system called PAILs and RAILs. PAILs stands for “progressive angular isometric loading” and RAILs stands for “regressive angular isometric loading”. The word isometric means that you will be contracting muscles without changing their length or moving from the stretch position.
Active Mobility Training – PAILs and RAILs
Translated, PAILs involve contracting the tissues that are being lengthened while in the stretch position. RAILs involve contracting the tissues that are being shortened while in the stretch position. PAILs and RAILs should be performed in a sequence that begins with a 1.5-2 minute passive stretch followed by a 15-second contraction of the lengthened muscle (as if to push out of the stretch), then a 15-second contraction of the shortened muscle (as if to pull further into the stretch), and finally a 30-second passive stretch to finish. You can repeat the sequence of isometric contractions as long as range continues to increase when you transition from PAILs (lengthened muscle) to RAILs (shortened muscle) contraction.
Check out the images below for an example of PAILs and RAILs applied to hamstring mobility (puppy recommended for moral support).
Passive Stretch (1.5-2 Minutes)
During this phase, the muscles in your hip and leg should be completely relaxed as you hold yourself in the position using your arms.
PAILs Contraction (15 Seconds)
During this phase, you should be contracting your glutes (butt) and hamstrings (back of the thigh) as if to bend your knee and straighten at the hip (pushing in the direction of the red arrow). Remember that there should be no movement during this contraction.
RAILs Contraction (15 Seconds)
During this phase, you should be contracting your hip flexors (front of the hip) and quads (front of the thigh) as if to straighten your knee while bringing your thigh toward your chest (pushing in the direction of the red arrow). During this phase if you are able to move further into the stretch while keeping the intensity moderate, go for it.
Final Passive Stretch (30 Seconds)
Again, the muscles in your hip and leg should be fully relaxed.
What You Should Feel
Mobility work should not be painful. The sensation you should feel is a moderate-intensity stretch. It is important to recognize that unlike traditional stretches, training mobility in this way is truly end-range strength training. Just as with other forms of strength training, it is normal to experience mild muscle soreness for 1-2 days after. Also, keep in mind that cramps are extremely common with this type of training and are not cause for concern. Cramps, in this case, result from neuromuscular confusion – your brain is attempting to communicate with your muscles in a position they are not used to. If you get a cramp, try to work through it while maintaining the stretch position…they improve with consistent training.
There are plenty of other methods out there for training active mobility, but the most important components are moving into a stretch position and actively training both the lengthened and shortened tissues in that range. It is crucial that the load be appropriate for the joint and muscles in that range of motion (heavy weights should NOT be a part of mobility training).
Alright, so now you should have a good understanding of what the terms flexibility, active mobility, and passive mobility actually mean as well as how they relate to one another. Put into practice, virtually all mobility training should be performed actively. Active mobility training produces the longest-lasting results and translates most effectively to athletic performance. Furthermore, active mobility training can reduce susceptibility to injury. Passive mobility and flexibility training, on the other hand, can actually increase injury risk by widening the gap between passive and active mobility.
Now that you have this information, stop wasting time with boring static stretches. With proper active mobility training you will see faster results that last longer. Be on the lookout for more new content on my blog. You can learn more about me and my background here. Drop a comment down below if you have any questions!
Health Advice Disclaimer
This article provides examples that are applicable to many, but not all people. They are based on typical presentations seen in my personal clinical practice. This article provides generalized information on training, but can in no way take the place of professional evaluation and treatment by a licensed medical practitioner. It is impossible to provide 100% accurate diagnosis or prognosis without a thorough physical examination and likewise the advice given for management or prevention of any injury cannot be deemed fully accurate in the absence of this examination.
If you are currently experiencing any pain or injury, seek professional evaluation before undertaking any exercise program. Ensure that you are medically cleared for exercise before undertaking any exercise program. Significant injury risk may occur if you do not seek proper evaluation. No guarantees of specific outcome are expressly made or implied in this article.