From: Natural News

Not only is poor posture unattractive, it has serious negative health effects. Humans have muscle memory, which trains muscle fibers to perform a certain task or assume a certain position. This is the reason why poor posture gets poorer if not corrected. The muscles “remember” a position as being “normal”, when in fact it may be very abnormal.Poor posture reduces lung capacity, adds stress to the spine, accumulates muscular tension, and leads to a higher susceptibility to injury. Socially, poor posture is associated with depression and a feeling of dejection. …
Sit up at the edge of your chair with both feet flat on the ground shoulder-width apart. Imagine a string running from the ceiling to the top of your head pulling it upwards. As it pulls, each vertebrae separates and the natural curves of the spine become accentuated. Now tuck your chin in as if trying to touch it to the back of your head through your skull. This should provide a deep stretch to the muscles that connect the spine to the base of the skull. Take a deep breath in, filling the belly, and rotate your hands outwards bringing the shoulder blades together as if squeezing a pencil between them. Hold this position for 15 to 20 seconds and slowly breathe out and relax. After the first time performing this exercise, a noticeable change and feeling of comfortable upright posture should be evident. This may last for seconds to minutes depending on the severity of posture degradation. Repeat this exercise whenever it feels like poor posture is creeping in again. This will help change the muscle memory of poor posture to good posture. After some time, this proper seated posture will become automatic and poor posture will become uncomfortable.

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