Understanding Muscle Firing and Tension

Understanding Muscle Firing and Tension

 My intention in writing this article is to provide you with a bit more awareness of the types of muscle contractions, relationships between opposing muscle groups and how we can use our muscles effectively.

When we think about any muscle, there is any opposing muscle which will perform the opposite action. A useful metaphor is the action of opposing pulley cords; one pulls tight and the other lengthens, it is the same in our body.


Reciprocal Inhibition (R.I.):

  • Let’s take the biceps as the contracting muscle (known as the agonist), this will bend the elbow. The opposing muscle (or antagonist), the triceps will lengthen. Something else which happens as the agonist contracts is that the antagonist will relax. This is known as reciprocal inhibition, a useful and quick method of assisting a tight muscle to relax for therapists and individuals to practice. For example, if your hip flexors felt tight when cycling you could contract the glutes to aid the release.


Post Isometric Relaxation (P.I.R.):

  • Another useful method of relaxing a tight muscle is to contract it for ten seconds at 20% effort then relax, tonicity will be reduced, stretching and palpation will be better received.


Isometric Contraction:

  • The agonist and antagonist muscles contract and remain at the same length. Let’s say we are holding a weight in our hand with the arm forward, elbow slightly bent and static. We are neither bending nor straightening, in this example biceps and triceps would both be working to support the static weighted arm against the pull of gravity. The degree of tonicity between muscle groups would alter with a greater or lesser degree of bend (flexion) in the elbow and the amount of weight being held.


Concentric Contraction:

  • The agonist muscle shortens as it contracts; once again let’s think of the biceps, whose action is to bend the elbow from starting point of a straight arm.


Eccentric Contraction:

  • The agonist muscle lengthens as it contracts. For example, hold a weight in your hand with the elbow bent and then slowly straighten the arm to lengthen biceps during contraction.


Compromised Posture and Loading Effect:

  • Let’s consider the rounded upper back and co-existent raised chin, extended neck position, which is dysfunctional but operationally practical in that we now look forward and not down. The problem is that the muscles in the back of our neck/ shoulder (agonist) will be locked short to sustain this position, be under strain, become irritable and muscle fibres will shorten. The opposing muscle group (antagonist) at the front of the neck will be locked long and weaken. The antagonist may also become irritable and exhibit abnormally high tonicity in the effort of overcoming the constant pull from behind.



  • The recommended approach would be to lengthen and release the tight muscle first and then strengthen the weaker one to promote balance. In the example above, we would also need to consider what is happening in the chest, front of shoulders, in-between the shoulder blades and mobility of the upper spine in assessing the big picture.


Active Engagement Technique (A.E.T):

  • A little theory first. Healthy muscles have two basic phases, the active phase and the release phase. Muscles which have become irritable, tight and painful and partially or permanently in a state of contraction, they do not disengage properly, tissue texture thickens and is less pliable, blood supply can be reduced.

A.E.T. is the process of repeatedly switching a muscle on and off, usefully coupled with palpation to re-educate a healthy firing pattern, with the focus centred on the release phase.


Have a think about the reciprocal relationship of different muscle groups in yourself. Where may you be tight or weak and begin to piece the jigsaw together. I am always here to help in the context of therapist and teacher.

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