Back bends - The structural and functional physiology involved

• Strengthens lung capacity as if invites opening
• Stretches and tones the abdominal region
• Strengthens the legs, especially the hamstrings (retracts) & quads (extends)
• Stimulates the spine by stacking one vertebra on the next, spinal nerves are stimulated by this action
• Helps the nerves system to send clear messages by working the spine area, encouraging strength
• Release tension is shoulders, chest and hips
• Heating and extrovert
• Stimulates the nervous system
• Squeezes the kidneys
• Physiologically, the endocrine glands in the front of the body are stimulated – the pancreas which secretes hormones for carbohydrate metabolism, the thymus which regulates immune function and the adrenals which influence our general state of alertness and arousal.  The muscular activity produces heat, and increased circulation.  The opening of the chest improves the capacity of the lungs to expand on the inhalation.  The sympathetic nervous system is stimulated.   Adrenals, fight or flight
• Improving posture and strengthening the spine
• Further to the general principles of backbends listed above, bhujangasana is particularly strengthening for the muscles that cause spinal extension – the erector spinae and the smaller semispinalis, multifidus and rotatores muscles that connect the bony processes of individual vertebrae.  The muscles at the front of the body are stretched – psoas and illiacus muscles (hip flexors), the quadriceps muscle (hip and leg flexors) and the rectus abdominus muscles in the abdomen.  The triceps muscles of the upper arms are strengthened and the intercostal muscles and pectoralis major are stretched.
• Strong stretching position for the front of the body. Extend the diaphragm/ solar plexus region and free tangled nerves of tension.    An open chest allows us to breathe fully and properly and therefore improve our energy.
• Muscles:  Strengthening and stretching  muscles on the front side of the body; Strong back muscles; pelvic region, thighs; opening the heart, lungs, and chest, Strong back muscles, developed with backbends, make it easy to sit and stand erect all day long, so you are alert and comfortable more of the time.  They are rejuvenating. They encourage youthfulness by keeping the spine supple.
• Physiology:  solar plexus (bow). Great many nerves converge here.  Control the bodies response to stimuli ie fear, joy, despair, warmth, cold
• Glands:  Thymus gland (cobra). When our thymus gland is correctly functioning, inwardly we feel 'safe' and protected and therefore able to give out, to relax and share with others, to go out to meet life and embrace it fully. It is very subtle but observe yourself and your actions and attitudes when you are feeling vibrantly healthy. Contrast this to when you are feeling ill , vulnerable, or experiencing fear:  Our lives today are often lived in fear - fear of loss, fear of rejection, fear of ridicule, fear of being alone, fear of anything at all . Fear comes from the unknown - not knowing how or why or what - ultimately, it is fear of destruction, fear of death.  Backbending asanas like bow pose (dhanurasana) and urdhva dhanurasana the adrenal glands are activated/balanced.   It is the hormone adrenalin, produced by the supra-renal glands on top of the kidneys which gives us the drive, the will, the intent to succeed in life, to go out and win, to stick it out until we reach that special goal. But too much of that hormone constantly circulating in our bodies, will create the stress cycle with which we are all too familiar in today's world.   The over-stimulation of these glands will cause us to live our lives on 'red alert', in constant stress mode, which will ultimately lead to bum-out, breakdown and many physical ills, because the body's resources are spent and there are no reserves to fight illness and infection.  The aim of backbending asanas is to re-balance the production of adrenalin so that we always do have enough energy for dynamic effort and emergencies, so that we can achieve our goals, but notlive on red alert depleting our resources too much.