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What is PAIL’s (Progressive Angular Isometric Loading)™?

Created by Functional Anatomy founder Dr. Andreo A. Spina, PAIL’s™ is a trademarked technique utilized exclusively in the Functional Range Release™ and Functional Range Conditioning™ systems.  PAIL’s stands for Progressive, Angular, Isometric Loading.  The technique is utilized in conjunction with Functional Range Release™ techniques, as well as for neuromuscular rehabilitation efforts for various conditions such as tendonopathies (Tendonosis), muscle strains, joint dysfunction, ligament tears, etc.

With regards to soft-tissue release, PAIL’s™, similar to PIR (post-isometric ‘relaxation’) allows a temporary reduction in the stretch reflex threshold, thus immediately allowing an increased range of movement of a joint.  PAIL’s application however also develops strength in this newly acquired range in order that the body will expand its functional range of motion.  To further explain this we must first understand the basic premise of what is known as the ‘stretch reflex’.

A reflex is the body’s automatic response to a stimulus.  One such stimulus is stretch.   For reasons of safety, the central nervous system contains a built-in ‘governor’ system called the ‘stretch reflex’, which automatically and unconsciously determines what the ‘safe’ range of motion is for any given movement.  When a body’s tissue is lengthened past this point, the stretch reflex is triggered sending a signal to the central nervous system causing it to increase tension, tightening the muscle to prevent any further lengthening from occurring.

An example of this reflex in action occurs when you are about to twist your ankle.  As the ankle begins to twist, the fibularis group undergoes a rapid stretch.  This triggers the stretch reflex which registers that the muscle is exceeding its ‘normal’ range.  The reflex then causes a rapid contraction of the Fibularis muscle to prevent further twisting from occurring, preventing injury to the muscle itself, as well as the ankle ligaments (most of the time!).

As with many of the other built-in safe-guard systems of the body, such as the inflammatory reaction to injury, the sensitivity of this safety measure’s threshold is set much too high.  Therefore, while the potential for further safe movement exists, the central nervous system will not allow this movement to occur.  Thus, this ‘safe’ range is not determined by the actual flexibility or extensibility of the muscle tissue itself, but rather is the ‘decision’ of the central nervous system.

How then does your CNS determine the stretch reflex threshold? The threshold is set by two main factors:

1.  Your previous experiences:  Your central nervous system has a tendency to want to maintain the norm.  If your body is consistently held in a shortened posture, as would be the case with office workers, truck drivers, and even people involved in many sports such as cycling, rowing, etc., your body will automatically set the stretch-reflex sensitivity very high.  Thus, when a new range of motion is attempted, the governor (stretch reflex) activates causing the muscles to automatically tighten up to prevent the movement.  This explains the far too common Upper Cross Postural Syndrome seen in many office workers, presenting as rolled-forward shoulders and anterior head carriage creating a slouched posture.

2.  Your muscles ability to function at that particular range of motion:  If your nervous system determines your tissues are not strong enough to recover from, or to control a particular range of motion, the motion will not be allowed.  For example, when one attempt’s to sink into a splits position, when the point is reached where the CNS believes it no longer possesses the ability to utilize muscular contraction to raise you back up, or to safely control further lowering, the stretch reflex is triggered causing your muscles to tighten, thus preventing you from sinking further.

PAIL’s™ application in injury rehabilitation utilizes techniques which produce strength and endurance in increasing ranges of movement, thus extending the functional range.  When utilized with the Functional Range Release™ system it allows practitioners to simultaneously release tissue tension while commencing the rehabilitative process, which will:

  • teach the CNS how to maximally recruit muscle fibers
  • decrease the onset of muscular inhibition and wasting that occurs post injury
  • improve neural drive to inhibited muscular tissue
  • expand the range of motion in which forces can be generated (ie. expand the functional range)
3 Comments leave one →
  1. Taya permalink
    February 9, 2012 9:45 pm

    I have a question. What you stated about the stretch reflex sounds logical and I have been with a patient when this happened (this was 32 yrs ago) but what science is this based on? or What sources can you site? Thanks

    • February 16, 2012 3:54 pm

      There are many lines of research that support my concept of P.A.I.L’s. Regarding the workings of the stretch reflex…obviously you can delve into the basic physiologic research. But there are others…and more constantly emerging

      here are a few for you:
      Kimura et al. Gradual increment/decrement of isometric force modulates soles stretch reflex response in humans. Neuroscience Letters 347 (2003) 25–28

      Lindh M (1979). “Increase of muscle strength from isometric quadriceps exercises at different knee angles”. Scand J Rehabil Med 11 (1): 33–6.

      Duchateau J, Hainaut K (1984). “Isometric or dynamic training: differential effects on mechanical properties of a human muscle”. Journal of Applied Physiology 56 (2): 296–301.


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