Flexibility vs. Mobility vs. Stability by Paul Smith
We commonly hear the terms “flexibility”, “mobility”, and “stability,” but what exactly is the meaning of each of these terms, what are the differences between them, and how do we train for these qualities?
Flexibility (Passive Mobility)
The American College of Sports Medicine (ACSM) defines flexibility as: “the degree to which a joint moves through a normal, pain-free range of motion (ROM).” Physical therapist Gray Cook describes flexibility as “passive mobility.”
Flexibility may be influenced by joint structure, which can vary from one individual to the next, the health of soft tissue around the joint, the length of antagonist muscles (those opposite the joint from the target muscle), and the temperature of the tissues surrounding the joint — flexibility tends to be greater when the tissues are warmer.
As an example of flexibility — or passive mobility — think of lying on your back, and then someone holds your foot and lifts your straight leg as high as they can. The maximum angle to which your leg can be raised while keeping the knee straight without tilting the pelvis is your flexibility (or passive range of motion/ROM) for flexion of the hip joint.
Gray Cook recommends improving your flexibility with these three practices:
- Static stretching: one or more sets of holding a stretching position for 60-90 seconds
- Self-mobilization: stretching the hamstrings in a supine position with leg extended and a band around one foot — passively holding the leg in the upright position
- Self-massage techniques: using a foam roller, therapy ball, roller stick, or graston tool
- Professional massage: let someone else work out your kinks
We can think of mobility as being the extent to which we can actively move a limb in a joint. In the example above, if you were to actively lift your straight leg, without anyone helping, that would be your active ROM of that joint. It may not be the same as your passive ROM, and often isn’t. It may be influenced by muscular strength (e.g. of the hip flexor and quadriceps muscles to lift the leg, and of the abdominal and low back muscles to stabilize the pelvis), or by neurological factors. For example, if someone has once had an injury in this region of the body, they might have a subconscious blockage from lifting the leg to the extent that would previously have caused a pain reaction.
Gray Cook states that mobility problems are movement dysfunctions, which may be the byproduct of inappropriate movement, or could be the result of a poorly managed injury, physical or emotional stress, postural stress, or inefficient stabilization.
Physical therapist Kelly Starrett defines mobilization as: “a movement-based, full-body approach that takes into account all the elements that limit movement and performance…. short and tight muscles, soft tissue and joint capsule restriction, motor control problems, joint range of motion dysfunction, and neural dynamic issues (tissues that do not slide over the nerves correctly)…. mobilization is a tool for improving your capacity to move and perform efficiently.”
Cook recommends improving active mobility with these practices:
- Dynamic stretching: going into and out of a stretch for 10 repetitions, with a one- to two–second hold at each end of the range
- PNF stretching: similar to static stretching, but with active engagement about a certain muscle group. Read more on that here.
The ACSM defines stability as: “the state of remaining unchanged, even in the presence of forces that would normally change the state or condition…. the state of a joint remaining or promptly returning to proper alignment through an equalization of forces.”
Gray Cook describes stabilizers as muscles which control movement in one local segment while movement occurs in another, and as muscles which create supportive tension within multiple global joints in order not to move in the presence of movement. This is in contrast to prime mover (agonist) muscles, which are the main muscles which contract to produce movement of the joints.
Kelly Starrett states that in order to create global stability about a joint, we need to first organize our spine in a neutral position, and then engage the musculature of the trunk. He goes on to describe specific rotations from the hip and shoulder joints to create stability in those limbs.
I discussed Starrett’s ideas on limb stability in a previous blog post: as a general rule, when the arms are in front of the body or overhead, external shoulder rotation creates stability; when the arms are behind the body then internal rotation creates stability; likewise when the legs are in front of or underneath the body, external rotation from the hips creates stability; when the legs are behind the body, then internal rotation creates stability.
Cook recommends that we: “Train stability with exercises that are more dynamic with the highest movement quality possible, and when dynamic quality cannot be achieved, revert back to static postures where alignment can be challenged.” For example, we could practice a step-back lunge to train stability. If we are unable to do the movement correctly, we could first practice holding a passive lunge position, with a partner lightly pressing on our body from different directions, to help us engage stabilizing muscles to hold the position. Once we have mastered that exercise we could return to the step-back lunge.
The ACSM recommends these three strategies for training stability:
- Have a stable base from which forces are transferred.
- Have adequate muscular capacity (strength and endurance).
- Utilize central nervous system programming, integrating sensory input, to produce synchronous activation of the stabilizing muscles.
Gray Cook states that: “Mobility must precede stability.” Motor control exercises to improve stability are only effective if mobility is not compromised. When mobility is compromised, we can develop patterns of holding stiffness and increased muscle tone to provide functional stability. More ideal would be to have full mobility and utilize more sophisticated motor control mechanisms to achieve stability.
In the example above of the activity mobility straight leg raise, we can think of how we engage the abdominal and low back muscles to stabilize the pelvis in a neutral position as we raise the leg.
Thinking about good alignment while doing exercise movements will help train stability. We can do exercises that challenge our balance, such as movements from a position where we have a narrow base of support.
So to conclude, we can see that relationships exist between these three abilities. Active mobility is probably more important to our performance of exercise movements and activities of daily living than is passive mobility. Stability is necessary to support actions of the main prime mover muscles during exercise movements. And having strong stabilizing muscles helps us avoid injury and avoid falling, whether during exercises or during daily life activities.
Paul Kevin Smith has a M.Ed. degree in Kinesiology from U.T. Austin, and is a Level 2 certified provider of the Functional Movement Screen. His other certifications include ACSM Clinical Exercise Physiologist, ACE Health and Wellness Coach, PhysicalMind Institute Pilates Mat Work Instructor, Experienced Registered Yoga Teacher (500 hours), and IAYT Yoga Therapist. Paul is an Adjunct Professor of Exercise Science and Student Development at Austin Community College, and also teaches yoga and Pilates classes and leads personal training sessions at BodyBusiness Fitness Club.
Paul offers Functional Movement Screens at CrossFit Renew. In this session he analyzes your mobility and stability in performance of ten movements. You will receive a report detailing your results, and a personalized exercise program to improve your functional performance. 60 minute session: $75.