Yoga affects us as a whole. As well as eliminating stress, charging the immune system and reducing age-related degeneration it offers flexibility, strength and an increased understanding of how your body works. Below is a breakdown of the different ways yoga affects the body.

Digestive system
Most of the time we just let our digestion just get on with things. But we can help by stretching and developing muscles in the stomach and internal organs. Back bends pull the stomach away from oesophagus and the diaphragm - thus increasing tone and reducing the tendency to herniate. By stretching and manipulating our digestive system the intestines get massaged, peristaltic activity is improved and absorptive capacity is toned up. IBS and heartburn are aided by the gentle stretching and compressing of twists, massaging and increasing circulation to the area.

Respiratory system
Regular yoga practitioners have oxygen uptake levels equivalent to that of moderate athletes. Principally this is because yoga expands the elasticity of the inter-rib muscles, thus maximising lung capacity. This is especially the case in forward bends (which stretch the posterior part of the lungs) and pranayama which open the alveoli (sacs that contain air in the lungs) so gas transfer is improved. Oxygen capacity usually diminishes with age as the ribs stiffen, but practicing yoga loosens these muscles, reversing the effects of age.

Circulatory system
Yoga strengthens and maintains flexibility in the heart and blood vessels. This can be seen on ultrasound taken during practice - the heart changes shape in response to different postures. Yet because yoga is less coronary-intensive than other exercise regimes, less lactic acid builds up in the muscles and this in turn avoids fatiguing the circulatory and skeletal systems. Backbends develop the cardiac sphincter as well as the anterior and lateral walls of the heart so blood flow remains strong. Furthermore inversions and restorative postures give gravity a chance to work out the blood vessels in a new way, reducing formation of varicose veins, for example, and increasing circulation to the brain.

Endocrine system
The endocrine system monitors and produces hormonal secretions that regulate body activities. Largely controlled by glands, this system is centred in two areas: the thymus in the mid-sternal area and the thyroid in the neck. When functioning well, this system creates a healthy balance (homeostasis) within the body, maintaining the strength of the immune system and increasing resistance to illness. The act of stretching elongates both muscles, organs and glands, flattening and squeezing out venous blood, leaving them ready to accept a complete dose of freshly oxygenated blood. Thus asanas which affect the endocrine glands (shoulder stands or backbends) maintain them at full vitality.

Skeletal system
Weight bearing exercises stimulate osteogenisis, or bone-tissue growth. So by holding your body in different ways, postures promote bone strength in different areas. Standing poses, especially balances, create and maintain joint stability in hips, knees, and ankles, while inverted postures such as Downward-Facing Dog build stability in the shoulders. Twists and inversions keep the spine strong.

At the same time a yoga practice builds up the muscles that support the skeleton. Chiropractors manipulate the joints of the spine to realign them, but if the muscle tissue that connect to the spine are not balanced and strengthened then the adjustment is only temporary. In the long run, treating the root cause of the misalignment is the safest - and cheapest - method.

Muscular system
Yoga is one of the few physical practices that increases both muscular strength and flexibility. Research done at the University of California showed that after only 8 weeks of practicing yoga subjects' strength increased by 31%, muscular endurance by 57% and flexibility by 188% (Bauman, 2002). This has a direct impact on the quality of life: simple things like getting up from a chair, walking up stairs or opening a jar become effortless. Yoga offers protection from things like repetitive strain injury as it balances opposing muscles and stretches over tense ones. By maintaining a healthy, strong muscular system yoga makes movement easier, and protects against strain.