1. Explain the concepts of joint complexes and muscle groups.
Joint complexes are a series of individual joints that work together. There are 9 important joint complexes in the body (15 in total including 6 pairs) compared with 650 individual joints.
They are: the ankle, knee, hip (includes the sacral and pubis), waist or lower back (lumbar spine), chest or upper back (thoracic spine), neck and head, shoulder, elbow, wrist (includes the hand) joint complex.
Various movements take place at the different joint complexes, involving the different muscle groups. Muscle groups are a set of muscles that cross a particular joint, that have the same function around that joint.
There are 6 primary and 3 opposing pairs of movement, that is; flexion (to bend closer to the head or face) and extension (to straighten away from head/face); abduction (to take away) and adduction (adding two parts together); internal rotation (to move in) and external rotation (to move out).
2. The practical study of the body can be made simpler by using the concepts of joint complexes and muscle groups. This saves one from trying to work with individual muscles and individual joints with which there are hundreds of names!
For example, the knee has 16 individual muscles with the purpose of bending (flexing) or straightening (extending). Referring to the different muscles involved in this particular action as the two opposing muscle groups, that is the knee flexors and knee extensors, then the purpose of the knee can be more easily described.
The hip flexors are another example of all the muscles that cross over the hip joint when activated that create hip flexion. Similarly for the group of muscles that cause hip extension when activated over the hip joint are called hip extensors.
3. Muscle activation and relaxation can occur in 4 different states around a joint complex. When one muscle group is activated, or performing the specific action, it is known as the agonist. This triggers what is known as the reciprocal stretch reflex, where the opposing muscle group known as the antagonist, must relax or stretch and lengthen, in order to perform the desired movement.
The four main states that can be created with muscle activation and relaxation around each of the 9 main joint complexes are:
*agonist and antagonist are both relaxed, that is essentially a passive stretch, and not ideal in practising hatha yoga as it can cause the stretch (myotatic) reflex to happen
*agonist is tensed or activated and the antagonist is relaxed known as the reciprocal stretch reflex
*agonist is relaxed and antagonist is actively tensed, great for when already in a yoga pose to safely lengthen the opposing muscle group further, as created with the inverse myotatic reflex
*agonists and antagonists are simultaneously tensed ie a bandha or co-activation of both opposing muscle groups around a joint complex, that is very helpful to lengthen and strengthen the muscles around the joint complex as well as develop stability in the asana and vinyasa.