In Yoga there are two things that stop your body from going further into a pose and we call them tension or compression. But what is tension and when to we experience compression? In Bernie Clark’s book Your Body Your Yoga he explains it like the following:
Tension is what we would call a stretch yet with stretching often people think they have to make something longer. When we think of the function of Yin Yoga, stressing our fascia, we learn that fascia barely stretches because it’s a tougher tissue in the body. For example when you wake up in the morning with the body being more stiff than when you went to bed before. The stiffness in your body will limit your range of motion when you would go into a seated forward bend trying to touch your toes. The tension then could possibly be felt in the hamstring area or along the back of the spine. With time and dedication you might develop more mobilty and flexibility in the areas you feel tension.
Compression is usually felt on the opposite side of a stretch (sometimes we feel both). Compression happens when two tissues meet and touch. In our bodies this could be bone on bone, bone on muscles, muscle on muscle, muscle on fat tissue or fat of fat tissue. Now imagine you push your hand against a wall. You cleary hit compression and are unable to go with your hand beyond the limit the wall is giving you. When we hit compression in our body this is the same situation. When for example you wake up and do your forward bend again and the front of your hipbone (ilium) touches the thighbone (femur) there is no way you can go beyond this point. You hit compression and the forward movement of your spine gets limited. With all the love and goodwill in the world you cannot go beyond compression without injury. You can adjust something in your body (moving the femur away from the compression with the ilium, if possible) which will remove the compression and help you get into your stretch again.
**Reminding you that going further is not more advanced or better. In Yin Yoga you need to feel your target area with the use of tension or compression and still be able to relax. If one of those is not the fact change your pose as there are many more poses with the same target area helping you harmonize the flow of chi.