Anatomical description of paschimotanasana

1. adduction of the shoulders on the frontal plane until arms are
perpendicular to the ground
2. adduction of the hip joint on the frontal plane until the feet touch
3. flexion at the hip joint on the sagital plane (idealy) until the
upper torso touches front of legs
4. (after grabbing big toes with hands) flexion of elbow joints on sagital plane
5. depression of scapula

Anatomical description of Utthita Trikonasana

The following is a description of the asana Utthita Trikonasana in anatomical language:
From the neutral position in the sagittal plane, step the right leg back 90 degrees in the frontal plane (feet around 3 feet apart). Square the hips to the sagittal plane, and externally rotate the right thigh. Retract the scapula and abduct the arms parallel to the floor.
Exhale and laterally flex the torso over the right leg in the frontal plane reach down and hold the ankle, big toe or place the palm on the floor outside your right foot (without rotating the hips). Extend the left had towards the ceiling, gaze at the left thumb. Hold for five breaths, and repeat on the opposite side.
Precautions: engage the kneecaps and quads, be careful not to hyperextend the knees.
The benefits of this pose are that it:
Stretches and lengthens the thighs, knees and ankles
Stretches the hips, groin, hamstrings, and calves, shoulders, chest and spine
Stimulates the abdominal organs
Helps to relieve stress
Improves digestion
Helps to relieve the symptoms of menopause
Relieves backache (especially through the second trimester of pregnancy)
Therapeutic for anxiety, flat feet, infertility, neck pain, osteoporosis and sciatica

Yoga and the spine

Recently a friend of mine had major back surgery, and complained to me that his functionality didn’t seem to be improving. I asked if he had been given any basic exercises to help improve his mobility during his recovery and he said he hadn’t. I felt sure yoga could help him improve his condition and recommended as such, since I have been interested in how Yoga can benefit the spine and our overall functionality.
The spine is an essential part of our bodies overall system contributing to our overall stability and structure, housing our spinal cord (which transmits neural signals between the brain and the rest of the body) and provides us with great flexibility and mobility.
As these systems evolved over millions of years and became crucial to our survival, they required the development of a protective structure that allows for free movement, but is stable enough to offer protection to these delicate tissues.
From an engineering perspective the human structure is the least mechanically stable of all creatures, which is where Yoga can help.
There are generally thought to be four possible movements of the spine, flexion, extension, axial rotation (twisting), and lateral flexion (side bending). These four movements occur spontaneously in everyday life, however there are of course yoga postures that emphasize these movements as well.  There is also a fifth possibility of motion called axial extension, however you have to learn to invoke this particular motion intentionally as it is somewhat unnatural.
Studies have shown that those who practice yoga as little as twice a week for eight weeks make significant gains in strength, flexibility and endurance, which is a basic goal for rehabilitation programs for back or neck pain.
Spinal twisting asanas are an important series for spinal health. The twist imposed on the spine and the whole trunk exercises the muscles, makes the whole spinal column more flexible and stimulates the spinal nerves. They also have a strong influence on abdominal muscles, alternately stretching and compressing them as the body twists from one direction to the other.
Forward bending asanas generally speaking are a passive process in which gravity is utilized to stretch and pull the body forwards. These postures help to loosen up the back, maintaining good health and increasing vitality. These types of postures move the body into a position known as the primary curve (or the fetal position taken in the womb). During a forward bend asana each of the vertebrae is separated, stimulating the nerves, improving circulation around the spine and nourishing the spinal cord. This group of asanas is also very important for making the back muscles supple and strong.
Back bending asanas stretch the abdominal muscles, and tone and strengthen the muscles controlling the spine. The spinal nerves, which emerge from the adjoining vertebrae, are decompressed. This has beneficial repercussions throughout the body since these nerves give energy to all the other nerves, organs and muscles within the body. Research has shown that 90% of backache is a result of muscular imbalance. If these balances are prolonged then the vertebral column in misaligned, the ligaments are strained and the symptoms of back pain begin to manifest.  The practice of a balanced regime of forward, back bending and twisting asanas can correct postural defects and address neuro-muscular imbalances in the vertebral system.
In addition the breathing and meditation aspects of yoga include a ‘relaxation response’ that has been found in many studies to assist people in decreasing their pain. Yoga has also been found to be helpful in the treatment of depression and anxiety that often accompany pain problems.