PNF Stretching

If you’re looking to increase your flexibility and improve your range of motion, you may have heard of PNF stretching. But what exactly is it, and how does it work? In this blog post, we’ll explore the ins and outs of PNF stretching, including what it is, how it works, and the benefits it can provide.

How Does PNF Stretching Work?

Before we get into those mechanism, we need to first understand 2 organs that work on those mechanisms

Basic Anatomy

Golgi Tendon Organ (GTO)

This organ sits in the muscle tendon unit. It is sensitive to change and rate of muscle tension. This organ works as to protect the muscles from injury

The GTO sends a signal to the brain regarding muscle load. It establishes a “set point” for how much the muscle can tolerate. If there is a load greater than this set point, it tries to shut the muscle down to avoid injury. Naturally this doesn’t always work

An easy example of how this works is a pullup for improving overhead ROM. At the bottom, the lats get a stretch. The GTO activates, allowing more range overhead. The lats usually limit overhead motion but by exercising them through their full range, overhead ROM is improved

The golgi tendon organ is a key component of PNF stretching

Muscle Spindle

This is a stretch receptor. It detects changes in muscle length

It works with a mechanism called the stretch reflex. All this means is that as a stretch is applied to the muscle, the spindle sends a signal to contract the muscle to decrease the stretch rate. Now that we understand the anatomy, we can dive into how it works

The muscle spindle is an important component of how PNF stretching works

Autogenic Inhibition

When a muscle is fully stretched or shortened it loses excitability (ability to reply to a new stimulus). Think of a bell curve

Increased muscle tension causes the activation of the GTO. This then allows the muscle to relax. PNF involves creating muscle tension in a lengthened state to allow this relaxation

Autogenic inhibition is a driver of how PNF stretching works

Reciprocal Inhibition

This is a big way to say that as one muscle activates, the opposite muscle relaxes and vice versa. Use the quads/hamstrings as an example. To fully shorten the hamstrings and bend the knee, the quads must reach a fully lengthened state.

This is also a protective mechanism to help prevent injury. In this mechanism the muscle spindle is at work. Reciprocal inhibition is one of the reasons you can have plenty of mobility without ever stretching

Lets look at overhead shoulder mobility as an example. Typically the lats limit overhead ROM. However, when doing an OH press, the front delts are working. They have the opposite function of the lats. This forces the lats to relax, improving shoulder flexion

Stress Relaxation

Occurs when muscle tendon unit is under constant stress/ Muscle and tendon have viscoelastic properties. This means they resist strain and then return back to the original form

This property of muscles allows them to be stretched without any damage to the tissue. Over time the viscous component loses its properties and the muscle increases in length

This is known as “creep”

As the stretch is held, the stiffness continues to decrease and ROM improvements are made. However, this is short lived, 80 seconds to an hour

Gate Control Theory

The gate control theory suggests that we can override the stimulus going to the brain and reduce pain. Simply, if pain is stimulus A, we provide stimulus B. This prevents the pain from being sensed

A large force is created when a muscle is elongated and then tries to resist the stretch. This force is sensed as a noxious stimulus. This stimulus can also activate the GTO

As the process of PNF goes on, the GTO becomes more accustomed to the noxious stimulus. This allows greater muscle length as well as improved force generation

How To Perform PNF Stretching

There are 2 primary types of PNF stretching

  • 1a. Contract Relax
  • 1b. Hold Relax
  • 2. Contract Relax Antagonist Relax

Contract Relax

  • The target muscle is lengthened.
  • Hold this position (I prefer 30 seconds).
  • Contract the muscle through a full ROM for 5 seconds.
  • Resistance is applied by the assistant.
  • Contract at 60% max capacity
  • Perform another stretch.
  • This process is then repeated.
  • I’ll usually perform these for 3 sets.
  • 1 set is a stretch followed by a muscle contraction

Hold Relax

  • Perform this the same as contract relax
  • The only difference is this uses an isometric contraction.
  • Nothing else changes

Contract Relax Antagonist Relax

  • Lengthen the target muscle
  • Isometric contraction for 5 seconds
  • Contract the antagonist for 5 seconds
  • Repeat the process

Reminder, although PNF will absolutely improve ROM immediately. It is NOT permanent. The gains last around an hour and a half at most

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