One of the key benefits and primary interests for people doing yoga is to increase flexibility and joint range of motion. I have compiled expert opinions on the physiology of stretching.
Muscles, tendons, and ligaments have an ‘elastic edge’ where by they can stretch to a certain length under force and then return to resting length. Overall, there is a set ‘length’ for the elastic edge of all these tissues. Muscles have a much longer edge than tendons and ligaments. Once this edge has been passed, tearing and damage readily occurs. As we develop our flexibility over time, we can readily adapt into the muscular edge and pass too much force into the shorter ‘edges’ of other connective tissue – this is where we see the onset of impingement, tendonitis, bursitis, and connective tissue tears occurring. It is common for those beginning a yoga practice to see significant flexibility gains in muscle tissue – just remain mindful that tendons and ligaments required greater adaptation time.
Sensitivity to Elastic Edge:
As we progress with consistent flexibility training, it is common with increased range of motion that we have decreased sensitivity to our true elastic edge by altering our reflex sensitivity in muscle stretch receptors. For those starting in flexibility training and yoga, they will feel a sense of stiffness and ‘resistance’ sooner than those who have been practicing for extended periods. This is part of protection mechanisms in muscle and connective tissue. With practice, we can override these mechanisms to allow us to ease into these edges with less sensitivity. The downside is, if we are practicing with ego, we do not have these mechanisms effectively telling us when to stop and become more susceptible to passing elastic edges and causing injury.
Doing a single yoga practice can create the sensation of tension release, but due to elastic qualities, tissues within minutes return to their original resting length. A single practice here and there will not increase overall flexibility and muscle length. Muscles lengthen by increasing the microscopic subunits called sarcomeres at the muscle-tendon junction. We can also manipulate the orientation of collagen in connective tissue to allow for SOME (note SOME in the limited sense) greater elastic length potential. The addition of sarcomeres and enhanced collagen orientation only occurs with regular, consistent, progress practices.
What Makes Me Feel Stiff:
Stiffness is partially related to overall muscle and connective tissue length. We can not change what is called technical “stiffness” without without adding on more sarcomeres or manipulating collagen orientation. We may experience extra stiffness due to muscle conditioning (force loads or stretching that cause micro-fiber tears … common in weight training programs). We may develop adhesions in fascia (connective tissue surrounding and supporting muscles). We may also have adhesions at the sarcomere-level in components called titin which are responsible for passive tension and for returning muscle filaments back to resting length after being stretched. In the case of fascial adhesions (often caused by dominance of poor posture or activities OR from injury), you may need to receive specialized treatments to break down the adhesions and prevent scar formation. Flexibility programs like yoga work directly on fascia to prevent adhesion formation and maintain fluid motion among the fascia and muscle. Stretching programs are showing to have some influence on titin – for example: longer titin units results in tension at longer sarcomere length, therefore being able to reach elastic limit at higher sarcomere lengths. Stretching may increase titin unit length especially in stretching programs with youth. Much more research is underway addressing the effects of flexibility practices at the sarcomere level.
Flexibility and Age:
As we age, we lose sarcomere units meaning reduced overall muscle length and increased stiffness. With age, we experience changes in collagen structure in connective tissue leading to decreased compliance in tendons and ligaments. Stretching programs can reduce the onset of these age-related tissue changes.
Stretching and Other Activities:
Progressive stretching has shown to reduce maximal force output of muscle tissue. Therefore, it is not advised to do deep stretching prior to activities requiring vigorous force generation. Instead, slow and gradual warming of tissues mimicking movements to be performed (easing through joint range of motion) in those activities is preferred. So, if you plan to do yoga and weights in the same day, best to do the yoga after your training.
Ideal Way to Stretch to Develop Flexibility:
Researchers have fully concluded that there is not enough research to adequately conclude what is the best way to stretch in order to develop flexibility. Given the vast number of variables: age, gender, predisposition to muscle fiber types, types of stretching, length of time, muscle isolation versus multi-muscle integration, goal specific training, etc, researchers are far from offering any concrete prescriptions. They clearly do recognize the benefits of stretching and most advocate exploring methods that your body readily responds to and suits your specific needs. This pretty much resonates the overall intention we should have within our practice: discover your uniqueness.