How to use Post Isometric Relaxation Post Isometric Relaxation (PIR) is a technique used to relax and lengthen a hypertonic and shortened muscle.  PIR cooperates with a muscle’s neural feedback system to accomplish a specific relaxation result on purpose. For example, a hypertonic upper trapezius muscle may restrict range of motion in the shoulder, head and neck.  By using PIR a therapist can relax and lengthen the muscle to increase passive and active range of motion and decrease pain. The steps involved in PIR are:
  1. Identify the target muscle to relax and lengthen
  2. Identify the target muscle’s primary action
  3. Contract the muscle isometrically using resisted motion for 6 to 10 seconds
  4. Stop the contraction and have the client breathe
  5. On exhalation of the breath, passively move the muscle in the opposite direction
  6. Gently lengthen the muscle to a new barrier of tissue resistance
  7. Hold at the new barrier for 2 to 3 seconds
  8. Release the new barrier by backing off slightly
  9. From this new position of ease, just off the new barrier of resistance, repeat steps 1 to 8
  10. Repeat 3 to 6 times to accomplish desired result
  11. All PIR steps can and should be performed pain free
The client’s breath has a systemic relaxation affect and adds to the ability of the muscle to relax. Relaxation window:  Following the isometric contraction there is a 10 to 15 second window of time during which the brain is sending inhibiting messages to the target muscle.  During this time the muscle is being “turned off” neurologically and is available to be passively lengthened. Stretch Reflex:  The stretch reflex is a protective reflex triggered when a muscle is lengthen beyond its current functional limit or lengthened too quickly.  Step 7 above holds the new barrier for 2-3 seconds.  This time limit stays below the threshold of the stretch reflex and allows the muscle to lengthen without contracting to protect itself.  Holding the new barrier longer than 3 seconds or moving into the barrier too quickly will trigger the protective stretch reflex and contract the muscle.  A stretch reflex contraction and tightening of the muscle would override the desired outcome of relaxed-lengthening.  Therefore, triggering the stretch reflex should be avoided.