Proprioception is our ability to know where our body is within space, and is created by a series of proprioceptors located in the tendons and the muscle fibres that monitor our tone.
Muscle tone describes the resting muscle activity, which can be influenced by many external factorssuch as temperature, mental and physical health and stimulus such as pain. Perhaps the best way to describe tone is ‘readiness to respond’. Normal tone is high enough to withstand gravity, but low enough to allow selective movement.
One category of proprioceptors sit parallel to muscles fibres, constantly measuring the tension within the muscle and refer the information to the spinal cord to ensure the muscle is is ready to respond. The golgi tendon organ is located in the tendon body, close to the muscle, and the pacinian corpuscle is located near the golgi tendon organ in the tendon; both are sensitive to change in tension throughout the connective tissue, and further the rate of the change of that tension. Most of our muscle tone is controlled through these mechanisms completely reflexively, never reaching further than the spinal column. Indeed, it seems strange to say, but as much as 90% of our 'voluntary' muscle activity occurs at a subconscious level.
Practices like yoga ask us to bring these usually subconscious mechanisms into our conscious awareness, deliberately structuring practice to enhance our bodies plasticity.
So, what are some of the reflexive mechanisms at action? And how can we utilise them to make our practice more effective?
- 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.
Moving into poses slowly and softly, then holding poses for longer periods of time allows the muscle spindles to habituate and therefore ultimately allows greater muscle length.
- Autogenic Inhibition (the lengthening response)
Golgi tendon organs 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.
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.
- Reciprocal Inhibition
Joints are controlled by two opposing sets of muscles, 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.
In postures, engaging the opposing muscle groups to those being targeted in the pose will ensure both that a greater level of stretch can be safely achieved, but also, that the co-ordination between movement will improve, meaning we will 'get in our own way' less.
Proprioceptive Neuromuscular Facilitation (/PNF)
When a muscle is stretched not all of the individual 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. Most importantly, it brings the 'stretch' wholly into our conscious awareness, ensuring it is integrated more deeply, and more quickly!
So... there is certainly a way to use your brain in yoga! But, you have to use it right, and that means off the mat too!
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.