Neurophysiology Of Asana
The Myostatic Reflex
When muscle spindles record a change in length, particularly a fast one, the stretch reflex attempts to resist the change in muscle length by causing the stretched muscle to contract in an effort to maintain muscle tone and protect the body from injury. This ‘stretch’ reflex is used daily as our body adjusts to gravity and balance, when we sense muscle fibres lengthening, then the contraction occurs to maintain our posture in relation to our environment.
Holding poses for longer periods of time allows the muscle spindles to habituate and therefore allow greater length.
Autogenic Inhibition (the lengthening response)
Golgi tendon organs (GTOs) are located around the musculotendinous junction and monitor the level of tension within their associated muscle fibres. If a muscle is contracted it produces tension through the tendon and wider fascial connections, hence stimulating the golgi tendon organs. If the tension reaches a point that is perceived as dangerous to the integrity of the muscle fibres or joint, the GTOs will fire, overruling the signalling from muscle spindles and instead causing the muscle to relax and lengthen.j
Holding poses for longer periods of time also allows the lengthening reaction to occur, helping the muscle being stretched to relax, however, this does not necessarily require high levels of tension. After approximately 10 seconds in a low-force stretch, the golgi tendon organs will respond, making it possible to safely stretch the muscle further.
Joints are controlled by two opposing sets of muscles, extensors and flexors, which must work in synchrony for smooth movement. When agonists contract, it (usually) forces the antagonist to relax, this accommodation of motion is reciprocal inhibition. As an example, the contraction of your bicep when you bend your elbow reciprocally inhibits the triceps to allow this motion to take place smoothly. This is not only true for muscles working around joints however, in gait, the activity of the anterior deltoid (as in a forward arm swing) will reciprocally inhibit the contralateral anterior deltoid to allow the backward arm swing.
Proprioceptive Neuromuscular Facilitation (/PNF)
When an muscle is stretched (much like when it is contracting) not all of the fibres are involved, therefore the length of the entire muscle depends upon the total of the fibres that are stretched. One way to increase flexibility therefore is to increase recruitment through fascial networks and the somatic nervous system.
PNF combines passive stretching and isometric stretching to achieve maximum static flexibility. Originally developed as a way of rehabilitating stroke victims this style has made its way into mainstream flexibility training. There are many different methods of PNF however, all function through a combination of passively stretching a muscle then adding and releasing isometric stretches at various intervals. In this way, PNF takes advantage of the immediate additional length acquired by isometrically stretching a muscle to work deeper into a posture. Additionally, by pre-fatiguing muscle fibres their ability to resist stretching through the stretch reflex is weakened, especially as additional fibres are recruited. Finally, PNF stimulates the golgi tendon organs to a greater degree than other forms of stretching encouraging the relaxation responses in the muscles and nervous system.
Use it or lose it... but use it right!
Davis’s law states that soft tissue will remodel itself along lines of stress* which conveys both advantages and disadvantages. When we practice a movement, our bodies remodel to become more adept at that movement, however, this is equally true for non-movements, or undesirable movement patterns that may be a necessary part of our lives. Sarcomeres will cannibalise themselves to change on a cellular level so as to become more efficient at what they do most. Therefore, we must be conscious to maintain global responsivity and avoid increasing ability in one area at the expense of another, in the form of muscle imbalances or instability that will encourage protective and contrastive mechanisms to activate.