A Practical Guide To Understanding Flexibility

Do your clients complain about their lack of flexibility? Can you see that their limited range of motion is causing them pain or functional problems – or holding them back from achieving their athletic potential?

Understanding flexibility and its neurophysiological underpinnings will help you to work with these clients more effectively and help them achieve their goals.

The Basics

Flexibility and Mobility are often used interchangeably, but they are not the same thing. Both are key to a complete client assessment.



Mobility refers to the ability of a joint to move through a specific range of motion (ROM). If someone is considered to have ‘Limited Mobility,’ that usually means that the range of motion of the joint in question is below average.

But everyone’s body is different, so it can be more helpful to compare a person’s mobility from one side to the other (bilaterally) than it is to compare them to another person.


Practical Step 1 – Assessing Mobility with the Passive Hip Flexion Test

Ask a willing guinea pig to lie down on the floor, face up. Use your hands to lift one left up until you start to feel resistance and see the body start to compensate, maybe by bending the knee or the pelvis starting to twist.

Back off a little bit until everything straightens out. That’s the end of that person’s passive range of motion. What you’ve just assessed is mobility through that range at the hip.

Test both sides and notice any difference between the left and right side. If there is a significant difference, then it would be accurate to say that person has a mobility issue on the side in question.



Flexibility is the ability to voluntarily control movement through to the end ranges of motion. It’s a measure of how much the muscles in question can stretch.

Static flexibility refers to the ability to hold a stretch without moving, whereas dynamic flexibility refers to the ability to move through a full range of motion.

Having the capability to perform movements and be strong at our end ranges has a dramatic effect on how resilient we are to injury. Improving flexibility should be a goal for anyone looking to improve the efficiency and efficacy of any movement, in daily life or in fitness training.


Practical Step 2 – Demonstrating Flexibility

Have your guinea pig assume the same position as in the first assessment. This time ask this person to lift a leg as high as possible on their own. This demonstrates the person’s flexibility.

In the untrained individual, you’ll normally find that the difference between mobility and flexibility is significant.


That Covers Flexibility and Mobility – What About Muscle Tone?

I heard it a million times when I used to be a personal trainer. I’d sit a client down in the consult room and start with the usual question: “So, what would you like to achieve in your exercise programme?”

“I’d like to get my arms and my belly more toned,” the client would say.

When people refer to muscle tone, a lot of the time they’re talking about being lean. A lower body fat percentage allows the muscles to be a bit more visible.

But for health and fitness professionals, tone actually refers to the resting level of tension in the muscle.

At any given time, our skeletal muscles have varying levels of tone so they can do their job of keeping us upright. Clients with a limited range of motion often have a level of resting tone that is too high.

To really get this concept and help clients address this problem, it’s helpful to understand the neuromuscular mechanisms that are at play here, including muscle spindles, Golgi tendon organs, and reciprocal inhibition.


The Neurophysiology of Muscle Movements


Muscle Spindles (Intrafusal Fibres)


Muscle spindles are sensory apparatus in the belly or middle of our muscles, and are a mechanism that monitors the length of the muscle fibres and the rate at which that length changes.

In a quick extension of the muscles, such as in a martial arts kick, your muscle spindles monitor whether the range of stretch and the speed of the stretch are within acceptable parameters for your particular muscle.

If the range is too far or the speed is too fast, muscle spindles facilitate muscular contraction as a protective mechanism, preventing further stretch. They are controlled both as part of reflexive spinal cord circuitry and via direct cortical (brain) control.

Neurologically speaking, when we static stretch a group of muscle fibres we are preferentially firing the spindle apparatus of that muscle.

If you gently static stretch a muscle group for approximately 8 seconds or less there will be an increase in motoric output (strength) of that muscle group, as the spindles have been sensitised.

But if you hold stretches for longer, the opposite is true. The spindles are desensitised and therefore the contractile capacity of the muscle tissue is temporarily reduced.




Golgi tendon organs (GTOs) are located around the musculotendinous junction and monitor the level of tension within their associated muscle fibres.

If the tension reaches a point that is dangerous to the integrity of the muscle fibres or joint (such as if you tried to lift a car), the GTOs will fire and the muscle will relax, releasing the tension.


Reciprocal Inhibition

reciprocal inhibition

Joints are controlled by two opposing sets of muscles, extensors and flexors, which must work in synchrony for smooth movement. Reciprocal inhibition is the process by which muscles on one side of a joint relax to accommodate contraction on the other side of that joint.

As an example, the contraction of your bicep when you bend your elbow neurologically inhibits the triceps to allow this motion to take place. It’s useful to imagine this as a push/pull type of relationship. If one side is pulling, the other side can’t also be pulling or no movement will take place.


So That’s How It Works – What Does It Mean?

Flexibility relies on all these neuromuscular mechanisms working together to allow a full range of motion. To increase ROM/flexibility, you have to stretch.

Some people in the industry have a negative view of stretching and say that it’s a waste of time or even dangerous. But there are many types of flexibility training, and matching the type of training to the client’s needs is critical to success. As with everything, specificity is key.

For example, holding static stretches for long durations before performing a skill that requires high levels of tension and strength probably isn’t the best idea. The muscle spindles will be desensitised and GTOs will be forcing the muscles to relax.

Joint mobility and the utilisation of simple spinal cord reflexes are far more effective interventions than static stretching, and they’re both taught as part of the AMN system.

If you understand how to work with human neurophysiology to increase flexibility, you’ll be able to help your clients integrate flexibility training into their exercise routines and daily lives in an effective way.


A Reality Check

No matter how much we might want to, we can’t all reach Olympic-gymnast levels of flexibility.

We all have different levels of collagen in our soft tissues, varying tendon and muscle lengths, differently shaped joints and bones, varying ligament tensions, disparate injury histories, etc. As professionals, we need to be mindful of that, and help our clients (and ourselves!) avoid unrealistic expectations and the possibility of injury due to overdoing it during training.

That said, good flexibility training meets the client where they are, and helps them to reach realistic goals.

Is everybody capable of achieving the splits? Probably not. But does everyone have the ability to improve on their current levels of flexibility? Absolutely!


What Helps Increase Flexibility?

In a world and industry where people are always looking for a quick fix, stretching doesn’t really fit the bill. Increases in flexibility are not quickly realised. It is an uncomfortable and time consuming process.

But increasing flexibility has many benefits for everyone, and flexibility training can be adapted for each person’s needs.

A lot of people I know and work with who have high levels of flexibility, both dynamic and static, tend to have been through a lot of painful stretching protocols as kids. We’re talking about gymnasts, high level track and field athletes, martial artists, dancers, and so on. They went through hours of flexibility training each and every week for years whilst at the most naturally flexible time of their lives. So of course they’re ahead of the pack when it comes to flexibility.

What if you, like most of us, didn’t take intensive gymnastics or martial arts as a child?

We can all learn from these sports even as adults, since they combine all of the factors involved in flexibility.

  1. High levels of dynamic and static flexibility required
  2. Static positional practice
  3. Dynamic flexibility practice
  4. Strength at end ranges of motion
  5. Frequent high volume practice (competitive gymnasts might spend 6hrs a week on flexibility)
  6. Control of respiration
  7. Acceptance while undergoing an extremely uncomfortable and laborious process

An exercise programme which includes these aspects will help to improve flexibility even for people who didn’t get a head start as a child.

This can be adapted depending on the level of flexibility one is trying to reach. After all, some clients simply wish to increase their limited range of motion, and need only the flexibility required for daily life and healthy regular exercise. Other clients, such as serious athletes, will of course require more flexibility training and a different exercise programme depending on their sport.

For example, if you are a weightlifter and can’t get your hands behind the barbell with ease or squat to full depth without your pelvis curling under, you need to work on regaining what should be a normal range of motion.

If, like me, your flexibility is holding you back from achieving higher and higher levels of strength and acrobatic skills, you need to practice the entire continuum of flexibility for several hours each week.

Flexibility training at appropriate times during any client’s exercise regime will help reduce the risk of injury and greatly enhance the outcome.

The Three Stages Of Flexibility Training

Joint Mobility Sequencing.

In this stage we’re utilizing novel, partially reactive, complex movement at the hip joint. This should be performed with just enough tension to maintain contact with the partners finger tips. Joint mobility sequencing provides a proprioceptively rich stimulus to the brain which has a parasympathetic (rest and digest) effect on the body, allowing increased range of motion to be experienced.

Loaded Progressive Stretching

In this stage I’m utilising isometric contractions to stimulate tension receptors, primarily in the hamstrings and gluts of the stretching leg. This is the basis of PNF stretching. As a muscle lengthens, the muscle spindles fire and cause the stretching muscle to contract, that’s what you feel as the ‘stretch’ sensation. Contracting the muscle while it lengthens stimulates receptors called Golgi tendon organs (GTO’s), which respond to tension. GTO’s quiet the spindle activity and allow greater range of motion.

We recommend 3 phases:

Phase 1 : 5 seconds of contraction, 5 seconds relaxation (be sure to totally relax the muscle and exhale following the contraction

Increase range of motion

Phase 2 :  10 seconds of contraction, 5 seconds of relaxation (be sure to totally relax the muscle and exhale following the contraction)

Increase range of motion

Phase 3 : 15 seconds of contraction, 5 seconds of relaxation (be sure to totally relax the muscle and exhale following the contraction)

Increase range of motion

Integrated Movement Practice

In this stage we like to utilize the relaxation of the muscles and new range of motion in gross, complex movement patterns. We can utilize the context of skilled movements to integrate new levels of flexibility with the whole body, and further develop range of motion whilst exploring multiple planes of motion.

This particular sequence provides stimulation to our inner ear balance system through level and direction change, which indirectly helps to keep all extensor muscles switched on and ready for action.


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1 Comment on "A Practical Guide To Understanding Flexibility"

  1. A great read, thanks.

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