Sometimes muscles get very tight and stay that way for a long time. Typical examples are the muscles that lift the shoulders, namely the upper trapezius and the levator scapulae, the hip flexor group: the muscles that lift the thigh up, or the hamstrings: the muscles that bend the knee.
Because they are so used to being tight, they do not respond to stretching. When we try to stretch them we either feel no stretch at all or the muscle just feels un-stretchy/blocked. So one way to overcome this is to use the PIR muscle energy technique to help them let go a bit.
To do this we take the muscle to a shortened position. For instance, with the upper trapezius (the upper part of the muscle marked in bright red to the right) we lie on our side in a foetal position, head on a pillow, resisting the temptation for a wee snooze, and gently raise the top shoulder towards the ear. Place the other hand on top of that shoulder and gently press the shoulder up further into the hand, giving a slight resistance to the move and possibly slightly lift the head off the pillow without twisting the neck. Hold there for 5 seconds. I stress this is gentle stuff. Work too hard here and we can misalign the neck. Then relax. Repeat 2 more times. Then after the 3rd contract/relax gently press the head down into the pillow and reach down the body with the top arm. Hopefully now we feel a lovely stretch down the side of the neck.
PIR is short for Postisometric Relaxation. How does it work? Well according to Leon Chaitow, in his book Muscle Energy Techniques, no one really knows. But it is true that immediately after contraction, a muscle relaxes for a brief window of 5 – 10 seconds and this is when we can take a useful stretching opportunity.