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March 2 2022 10:36 AM

Which one are you training, and why does it matter? 


Can everyone learn to do the splits? Coming from a background in sports medicine, dance medicine, strength & conditioning, yoga and Pilates, this is a question people often ask me.

The short answer is “no.” Not everyone can attain this range of motion. Now, let’s look at not only the “why” behind this, but also the bigger picture.

Do you coach clients on flexibility or mobility? More importantly, what is the difference, and how does this affect a client’s movement abilities?

With the rise of niche marketing and social media, the lines of “flexibility” versus “mobility,” have become blurred. Let’s begin with what each word means, and how they are not the same. The delineation can shed light on which your client needs, so you can then select methods to help your clients set realistic goals and an efficient path toward success.


Flexibility is the ability of muscles and their surrounding soft tissues (fascia, ligaments, tendons and nerves) to passively lengthen. Passive means that a force outside of the client’s own body creates the motion. Forces could come from body weight against the floor or another object, stretch straps or a fitness professional’s use of hands for assisted stretching.

Flexibility is not the same as stretching. Stretching represents a variety of exercise methods to increase flexibility. Flexibility is the soft tissues’ internal response to stretching exercises. Biomechanically, the main component of flexibility we target with stretching is extensibility. Extensibility is the soft tissues’ ability to lengthen when stretching force is applied, then return to resting length.

Effective stretching requires lengthening the soft tissues across all of the joints that the tissues cross. This makes stretching positions to increase flexibility fairly specific. For example, when stretching hamstrings, a client is often on his or her back with the hip flexed, knee extended and ankle slightly plantarflexed. When stretching the rectus femoris (the only quadricep that crosses the hip and the knee), the hip is in extension and the knee is in flexion.

The concept of lengthening across all joints is not limited to single muscles or muscle groups. Instead, one could improve flexibility of a myofascial line. For example, the yoga downward dog completely lengthens the deep longitudinal sling system. The deep longitudinal sling system refers to the connection of the paraspinals, sacrotuberous ligament, lateral hamstring and peroneals. Notably, the client feels sensation across the lengthening side of all involved joints.

Improving flexibility requires effective stretching exercise prescription. Effective exercise prescription includes not only specific positioning, but also selecting frequency, intensity, duration and type.
Frequency: Daily
Intensity: 3/10 (meaning a gentle pain-free line of pull in the proper alignment)
Duration: 30-60 seconds for static stretches for 3-4 sets
Type: Static low intensity, long duration (30 sec +) stretches generally improve tissue extensibility. Type selection, however, may depend on client goals.

Even with regular stretching efforts, different clients will have varying results, as genetics also play a role in how quickly and how much soft tissues can change.

Key point: Low intensity 30-60 second passive stretches in specific positions that lengthen the target soft tissue across all of its joints can improve flexibility.


Mobility, in the traditional healthcare provider sense, is the ability of joint surfaces to move on each other in roll, spin and glide motions. These are subtle motions within the joint. No amount of stretching or exercise will change limited joint roll, spin or glide.

The term mobility, in the fitness sense, has taken on a slightly different meaning, however. General internet searches reveal a broader definition of mobility, as the ability of a joint to move actively or passively. Active movement implies that the client is moving his/her own joints by using his/her own muscles. Passively implies that an outside force, like the floor or another person, is providing the force.

Flexibility influences joint mobility, but it is only one component. For example, if you lie on your back and perform a hamstring stretch, chances are you are not able to keep your knee straight and get your hip to flex more than 90 degrees. However, if you bend your knee and hug your thigh toward your chest, you can probably attain more than 90 degrees of hip flexion. This illustrates the difference between hamstring (and posterior thigh soft tissue) flexibility versus hip joint mobility.

If flexibility is only one factor, what else can limit joint mobility?

Rigid structures:
  • Bone: We are not all built the same. Bones and joints have slightly different shapes and angles in each individual. Hip joints, in particular, have high structural variability.
  • Age-related changes: Bone surfaces change with forces upon them over time. Generally, as age increases, joint space narrows, offering less motion.
  • Youth have components of bone still made of cartilage; cartilage is softer than bone, so youth often have more joint mobility than adults.
  • Older adults often have cartilage degeneration; this creates irregular joint surfaces that do not glide as well as they once did.
Inert structures:
  • Capsule: Capsules surround each major joint; they blend in with the ligaments.
  • Ligaments: Ligaments connect bones to other bones.
  • Fascia: Fascia is like a soft tissue cobweb that intertwines with muscle fibers, bones, organs and even the nervous system. It has high levels of sensation, but it does not stretch like muscles do.
Extensible structures:
  • Tendon: Tendons connect bones to muscles; they are extensible, but not to the degree that muscles are.
  • Muscle: Muscles are extensible tissues; their level of flexibility may influence joint mobility.
Neuromuscular factors:
  • Bones, cartilage, fascia, ligaments, tendons, and muscles all have sensory endings. The way the brain and spinal cord receive and process information influence a client’s perception of attempts to improve flexibility or mobility. Deep breathing can play a major role in the neuromuscular factors, allowing greater mobility and flexibility.
Other factors:
  • Scar tissue: Scar tissue from previous injuries and surgeries is not very mobile. It can limit both flexibility and mobility.
  • Effusion: Effusion means swelling in a joint. If a joint is swollen, it should not be mobilized.
  • Synovial fluid: This fluid is inside of the joint capsules around each major joint. At rest, it is like thick mud that doesn’t move well. With warm-up or joint mobilization exercises, the fluid decreases viscosity, flowing more like water.
With so many factors influencing joint mobility, it can be hard for fitness professionals to know where to begin. Fitness professionals can instruct clients in dynamic warm-ups through various motions to increase synovial fluid and fascial mobility and neuromuscular control. Examples include deep body weight squats and arm circles.

If these dynamic warm-ups involve passively lengthening a muscle or myofascial group across all of its joints, the selected movement is focusing on the flexibility component of joint mobility. A common example is the yoga sun salutation.

If a client is moving toward his/her end range of a joint motion and feels “stuck,” “pinch,” or “pain,” (especially on the closing side of the joint) fitness professionals should encourage the client to back away from this sensation, as opposed to pushing through it with force, bouncing or momentum. Adding a physical therapist and/or chiropractor to the client’s team can help differentiate the underlying sticking point. If the underlying limitation is a capsule, ligament or deep scar tissue, these professionals may be able to help. If the underlying limitation is bone or cartilage, the client may need to adjust movement goals to embrace structural limits.

Key points: Mobility drills are generally part of a dynamic warm-up to increase ease of joint motion. Mobility drills generally do not fully lengthen muscles across all of their joints, since the goal is increasing ease of movement at the joint surfaces. Numerous factors (such as bone shape, cartilage integrity, ligament and capsule health . . .) influence joint motion, and fitness professionals should not try to force a client past points of joint stiffness.


In conclusion, neither flexibility nor mobility are better. Your client’s goals, however, can help guide priorities.

If your client wants greater range and ease of motion with activities that do not require passively lengthening a muscle or myofascial line across all of the joints that it crosses, mobility drills are likely the answer. Outcomes look like a deeper squat, or more rotation in a golf swing.

If your client wants more motion that requires passively lengthening muscles or myofascial lines across all of the joints that they cross, flexibility is likely the answer. Outcomes look like ability to do the splits, a higher straight leg raise when lying on the back to stretch hamstrings, or achieving a wheel pose in yoga.

Flexibility and mobility, however, are not mutually exclusive. A shortened muscle can limit joint mobility. If this is true, the client will feel limitations on the lengthening sides of the joints; performing a stretch can increase the joint mobility immediately.

Conversely, limited joint mobility can limit flexibility. Joint mobility drills (often part of a dynamic warm-up), may or may not help. Many factors influence joint mobility. Limited joint roll, spin or glide cannot be fixed with exercise. These limitations feel “stuck,” or “pinching” on the closing side of the joint. Fitness professionals should not encourage clients to barge these barriers, but rather partner with the client’s physical therapist and/or chiropractor to assess underlying causes of the joint restriction.