Fascia And Flexibility
Flexibility is the ability to voluntarily control movement through to the end ranges of motion and can be static, dynamic and active. Essentially we are measuring the soft tissues capacity to lengthen both mechanically and neurologically.
Resistance to a muscle lengthening is highly dependent upon its connective tissues: When the muscle elongates, the surrounding connective tissues become more taut to maintain tensile support. Inactivity of a certain area (either historically or due to injury) leads to chemical changes similar to the natural ageing process within the connective tissue leading to stiffening; as the elastin ‘frays’ and collagen fibres thicken. Additionally there are increased calcium deposits and a cumulation of adhesions, and cross-links in the tissue. Increased fragmentation and dehydration, changes in the chemical structure of the tissues and replacement of muscle fibres with collagenous fibres. We all have varying levels of collagen in our soft tissues alongside varying tendon and/or muscle length, differently shaped bones, and different life histories. In healthy subjects, approximately 50% of collagen fibrils are replaced annually (this decreases with age) with suggestion that movement practices are vital to stimulating this renewal cycle.
According to Michael Alter: The joint capsule (the saclike structure that encloses the ends of bones) and ligaments are the most important factors, and account for 47% of the stiffness. Muscle's fascia accounts for 41%, the tendons 10%, and skin 2%. However, he also clarifies that the most effective way to approach increasing flexibility is through work on the fascia because it has the most elastic tissue, and further it does not impact the integrity of the joint. However, even this breakdown does not account for the interaction between fascial planes. Scar tissue for example will hinder the smooth sliding of the fascia creating resistance or ‘stuckness’.
We could argue that by working on the wider network of connectivity in the body, truly we are working on the whole self and that this will indefinitely be more powerful than an isolated joint by joint or muscle approach that is incapable of containing the wider aspects of the individuals experience. [the book Your Body, Your Yoga by Bernie Clarke offers a wonderfully in-depth explanation of the physicality of asana, and furthermore the vast array of individual differences in structure.]
Proprioception is our ability to know where our body to is within space. Proprioceptors involved in stretching are located in the tendons and the muscle fibres. Muscle spindle cells (extrafusil) sit parallel to muscles fibres, constantly measure the tension within the muscle and refer the information to the spinal cord to ensure the muscle is is ready to respond. Intrafusil fibres lie parallel to the extrafusil fibers and detect/feed back changes in muscle length as the extrafusil muscle fibres lengthen. 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. At the spinal cord level muscle tone, and most reflexive action is controlled, whilst the brain is fed up to date information on the bodies state. As much as 90% of our ‘voluntary’ muscle activity occurs at a subconscious level.
Muscle tone describes the resting muscle activity, which can be influenced by many external factors such 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.
Physical stretching (like contraction) begins with the sarcomere. The area of overlap between the thick and the thin myofilaments decreases allowing the overall muscle fibre to lengthen. Once all the sarcomeres are fully stretched, the muscle fibre is at its maximum resting length. In situe, a sarcomere can only stretch approximately 70% of its resting length, any additional stretching here places force on surrounding connective tissues. (Interestingly, if we remove the sarcomere from the body, we see that it is capable of far greater stretching, thus we can conclude the purely physically properties of the sarcomere are not the primary restricting factor in flexibility.) As tension in connective tissue increases the collagen fibres align along the same line of force as the tension to take up any remaining slack, and realign disorganised fibres.
Myers theorised that the smooth-muscle like contractions of the fascia and the rich network for communication with the central nervous system aid in stability and also importantly energy conservation by providing a pre-tensioned network that interacts with gravity. Human resting myofascial tone allows us to perform and respond with automatic movements, through a network of communication in the fascia, extra cellular matrix and peri-neural networks, that function both separately and in tandem with the nervous system. Connective tissue contains as much as ten times the amount of proprioceptors as muscle, which means our fascial matrix is able to reflexively interact with our environment faster than the conscious mind. Indeed, it is these systems that are now believed to underpin the meridians of traditional Chinese medicine, and as we will discuss in more detail later, the system of the nadis.
The mechanisms discussed below highlight some of the protective and facilitative aspects relevant to our discourse on yoga.