Each asana, or physical posture, has numerous benefits. These benefits often go much beyond the pure physical benefits, and include significant emotional, mental, and spiritual benefits. For the purpose of this article we will focus on the physical benefits and more specifically, the muscular activations.
Baddha Konasana (Bound Angle Pose).
The hip abductors, the sartorius draw the knees apart and toward the floor. The external rotators turn the thighs out, and the hamstrings flex the knees. Adductor Longus and Gracilis engage.
The left hip is deeply externally rotated to allow the foot to, ideally, sit in the hip crease. The right hip and knee are flexed deeply to allow the leg to come toward the body. The right hip is also adducted to bring the knee toward the left shoulder before reaching for the binding. Both shoulders are deeply internally rotating in order to reach around the right knee and the torso to bring the hands together for the bind. Finally, we are twisting deeply through the whole spine.
Uttita Hasta Padangustasana A/B/C
In this pose, Utthita Hasta Padangusthasana, the contracting of the various muscles helps to hold the body in balance along with gaining strength with the muscles. The muscles in the arms: the biceps (at the upper arm), triceps (at the back of the upper arm), brachioradialis (top of the forearm, near the elbow), extensor carpi radialis longus (close to the wrists), and deltoid (near the shoulder) all contract. The muscles in the leg which at considered the longest: the quadriceps (front of the thigh), the hamstrings (back of the thigh), the calf (above the ankle and below the back of the knee) all contract. Apart from the above we have the gluteus maximus (at the buttocks), the Psoas muscles (joining the hips and the thighs) that contacts during the practice of this pose.
When we lift our legs up into navasana, iliacus and psoas major (or the iliopsoas) primarily create that action since they are the strongest hip flexors. The quadriceps are working to straighten or extend the knee joint. The abdominals are working to stabilize the pelvis and torso relative to one another so that the iliopsoas can create the hip flexion.
Ado mukha Swanasana
Eccentric contraction of the hamstrings and the gastrocnemius (muscles crossing at the back of the knees). Soleus (muscles crossing the ankles with the gastrocnemius) are stretched when we dorsiflex the feet. When we straighten the arms, pressing the palms actively into the mat, pushing the body back toward the legs, it further deepens the stretch. When we deepen the stretch in this way we can allow ourselves to arch the lower back to give a full extension to the spine.