To this point, we have discussed the importance of exercising our connective tissue, as well as how the body can sense the changes that occur during yin postures and stretching. But once the external, biomechanical signal is converted into an internal, biochemical or electrical signal, how does this signal begin to change the fascia?
Biochemistry can initiate changes in the local environment in two primary ways. The first method in which modifications are introduced is through the direct alteration of the expression of genes involved in the composition of the fascia. When internal 
biochemical signals are initiated, a chain of dominos (in the form of proteins) begins to fall. As with dominoes, each protein’s behavior is determined by the actions of the previous protein in the chain. Eventually, when the last domino is reached, a final protein specific to the message being delivered will move to the central command station of the cell (the nucleus). This protein messenger initiates changes inside the nucleus by modifying the manufacturing blueprint for every protein component in the body, known as the DNA.
While every cell of the body contains a complete set of DNA (or coded manufacturing instructions), certain cells only 
produce certain proteins at specific times. This is why our stomach cells are not the same as the cells of the heart and why our skin cells behave differently when we need to repair a wound. The factors that determine which proteins are produced are these final dominos or messenger proteins (also known as transcription factors). The immediate needs of the cell determine which messengers are sent to the command station to bind to the DNA. This is an important step, as most messengers can only bind to specific portions of the DNA. In the case of yin postures, the cell will send forth messenger proteins that have the ability to bind to DNA segments that encode instructions for the fascial proteins, such as collagen or elastin. Once these messengers reach the blueprint, they will bind to the appropriate segment of DNA and initiate either an increase or decrease in the production of the target protein. During a yin stretch, production of proteins (such as elastin or tenacin C) associated with the more mobile, elastic components of the fascia are increased. These newly formed elastic proteins are then exported to the outside of the cell where they can be integrated into the fascial protein web.
A second way biochemical signals can induce changes in the fascia is through a process known as paracrine signalling. Think about how a smell expands and travels in all directions away from its source, affecting the behavior of nearby individuals—paracrine signaling works in much the same way. Once a central cell (the source) receives information that biomechanical changes are occurring in its surroundings, that cell will release biochemical factors that alter the behavior of neighboring cells. In the case of fascia, the cells most affected are known as fibroblasts, whose primary purpose is production of the fascial proteins. When fibroblasts receive a paracrine signal they alter their production priorities, upregulating production of some proteins, while down-regulating others. This altered production translates to changes in the external, mechanical environment in which the cells are suspended. During yin postures, the fibroblasts will increase production of elastic components and decrease production of tension generating components to create positive changes in the fascia.
Yin yoga also requires practitioners to hold postures for long durations of time in order to counterbalance the extended holds we place on fascia in our sedentary lifestyles. When a posture is held for several minutes, we allow the necessary time for biomechanical feedback to continually ignite biochemical signaling pathways that can alter the connective tissue. If we only hold yin postures for short durations, we do not allow time for all the dominos to fall and significant changes in cell signaling and protein production cannot be achieved. So while it may not be pleasant to hold dragon pose for four or more minutes, just take a deep breath and allow the body to do its work!
We need to begin to move out of the mindset that we are only “doing” something when we can see immediate, external changes. Active, muscular yang practices are important to combat our sedentary lifestyles. However, our sedentary lifestyles are hurting more than just our biceps—our facia and other connective tissues are also suffering. Therefore, just like we incorporate yang to exercise our muscular system, we also must incorporate yin to exercise our connective tissue. By exercising our fascia, we begin to untangle unseen, internal nets, allowing for more harmonious flow, movement, and well being.
Physiology of Yoga 