Question: what is the correct sitting posture and what is the degree of angle between the bottom and the back-rest? 

Answer: Identifying good posture\nBasically, having correct posture means keeping each part of the body in alignment with the neighboring parts. Proper posture keeps all parts balanced and supported. With appropriate posture (when standing) it should be possible to draw a straight line from the earlobe, through the shoulder, hip, knee, and into the middle of the ankle.\n\nBecause people find themselves in several positions throughout the day (sitting, standing, bending, stooping, and lying down) it's important to learn how to attain and keep correct posture in each position for good back support, which will result in less back pain. When moving from one position to another, the ideal situation is that one’s posture is adjusted smoothly and fluidly. After initial correction of bad posture habits, these movements tend to become automatic and require very little effort to maintain.\n\nIdentifying incorrect posture\nThe first step in improving posture is to identify what needs improvement by examining one’s own posture throughout the day, such as sitting in an office chair, carrying objects, or standing in line. At regular intervals during the day, take a moment to make a mental note of posture and back support. This should be done through the normal course of a day to best identify which times and positions tend to result in poor posture. Some people find it easier to ask someone else to observe their posture and make comments or suggestions.\n\nExamples of bad posture and back support \nThe following are examples of common behavior and poor ergonomics that need correction to attain good posture and back support:\n\nSlouching with the shoulders hunched forward\n\nLordosis (also called "swayback"), which is too large of an inward curve in the lower back\n\nCarrying something heavy on one side of the body\n\nCradling a phone receiver between the neck and shoulder\n\nWearing high-heeled shoes or clothes that are too tight\n\nKeeping the head held too high or looking down too much\n\nSleeping with a mattress or pillow that doesn't provide proper back support, or in a position that compromises posture\n\nExamples of bad posture while sitting in an office chair\nThe following bad habits are especially common when sitting in an office chair for long periods of time. \n\nSlumping forward while sitting in an office chair\n\nNot making use of the office chair’s lumbar back support\n\nSliding forward on the seat of the office chair\n------------\nPosture for a Healthy Back\nWhat is good posture?\nPosture is the position in which you hold your body upright against gravity while standing, sitting or lying down. Good posture involves training your body to stand, walk, sit and lie in positions where the least strain is placed on supporting muscles and ligaments during movement or weight-bearing activities. Proper posture: \n\nKeeps bones and joints in the correct alignment so that muscles are being used properly. \nHelps decrease the abnormal wearing of joint surfaces that could result in arthritis. \nDecreases the stress on the ligaments holding the joints of the spine together. \nPrevents the spine from becoming fixed in abnormal positions. \nPrevents fatigue because muscles are being used more efficiently, allowing the body to use less energy. \nPrevents strain or overuse problems. \nPrevents backache and muscular pain. \nContributes to a good appearance. \n\n\nProper posture requirements \n\nGood muscle flexibility \nNormal motion in the joints \nStrong postural muscles. \nA balance of muscles on both sides of the spine. \nAwareness of your own posture, plus awareness of proper posture which leads to conscious correction. With much practice, the correct posture for standing, sitting, and lying down will gradually replace your old posture. \nWhat contributes to bad posture?\n\nobesity \npregnancy \nweak muscles \nhigh-heeled shoes \ntight muscles; decreased flexibility \npoor work environment \npoor sitting and standing habit
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