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The provision of proper sleep and relaxation is one of the most important requirements in the home for the proper  functioning of the body, because it facilitates the rhythm of energy consumption and recuperation during work and rest. This rhythm is necessary because of the proper regeneration of the internal organs that is why people take rest pause during work to recoup up the energy which has been spent during work.
This sleep, work and relaxation cycle is controlled by two systems i.e. activating system `and inhibitory system.
Activating system keeps the organism awake, and keeps the organs in the state of readiness. It responds to all kinds of sensory stimuli, including noise, pain and light, thus it has a key position in the links between environment and the human body.
The inhibitory system works in opposition, reduces the readiness for action. Its output creates in the brain the sensation of weariness and it pulls the internal organs into the state of relaxation, assimilation and recuperation. The increased activity of the inhibitory system brings about sleep. So when the activating system dominates in the brain, the person feels fresh and ready for action, when the inhibitory system predominates, the subjects feel tired and want to stop work and relax.
Sound sleep is very important for the body. Repeated nights of reduced or disturbed sleep make the person feel in great stress, nervousness and irritability and also leaves dark circles around the eyes. Physiologists have repeatedly shown the cases of psychic disturbances due to the lack of proper sleep. During sleep certain recuperation processes occur, in which the redistribution of enzymes in the interior of the cells is of particular importance. Moreover physiologists assume that all the general processes of assimilation takes place a large extent during sleep.
So to give people the conditions necessary for sleep and relaxation in their homes one must reduce as far as possible all stimuli that will excite the activating system, only then the person can have the maximum relaxation and sleep. The room should have provision of furniture which ensures that the muscles relax as much as possible by holding the body in a natural posture.
Why the persons sit: Generally, sitting posture is adapted for relaxation, in addition to meet the needs of work. During standing posture there is fatigue for the body, because the joints of the foot, the knee and the hips are kept in position by the static contraction of the muscles. The blood and tissue fluids have a tendency to accumulate in the legs and the hydrostatic pressure increases. On the contrary, during sitting posture, the muscular effort is reduced and this reduction leads to a decrease in the consumption of energy and reduces the hydrostatic pressure in the veins of the legs and facilitate the flow of blood towards the heart. The interference in the circulation of blood during the standing posture is a source of fatigue. So the seats which are provided for sitting should promote the sealed attitude to reduce the strain of bending on the back to prevent the spine from developing curvature.
Disadvantages of the sitting posture:
- It slackens the abdominal muscles and curves the spine.
- It impairs the functions of certain internal organs, such as those of digestion and respiration.
- It imposes a strain on the principal support areas of the body and in the buttocks. The effects of heavy tissue pressure can produce the feeling ranging from discomfort to intolerable pain.
Sitting Postures:
Sitting posture can be of three types:
- Forward sitting posture - Working posture
- Upward sitting posture - Working posture
- Backward sitting posture - Rest and relaxation
When designing any seat (work, rest) it is important that it should give a comfortable normal spinal attitude with no strain on the vertebra. This spinal attitude can be achieved by having the lumbar vertebral nearly straight with a slight lordosis and preferably a flat back.
Sitting down with a 90o angle at the hip joint results in such a spinal attitude, where the weight of the upper part of the body is not properly distributed. The weight of the upper part of the back is thrown on the lower lumbar vertebrae, which is harmful for the lower discs and vertebrae. So, it is recommended that the backrest should slope well backward at the level of the shoulder blades and should project forward in the lumbar region. This facilitates the slight tilting of the back. During tilting the whole pelvis rotates forwards around the hip joint, as a result of which the sacrum, the lowest part of the spinal column makes a corresponding improvement and approaches the horizontal. This position produces lordosis of the lumbar vertebra which is a comfortable posture, keeps the backbone in a natural curve. Whereas on the pelvis rotates backwards and the sacrum assumes a more vertebral position, this flattens the lumbar vertebrae and produces kyphosis position which is very uncomfortable and a person can not sit in this posture for longer time.
During upright and reclining posture, the pelvis is rotated forwards and a lordosis is produced in the lumber vertebrae. In contrast, a forward sitting posture is usually accompanied by backward rotation of the pelvis with flattening of the sacrum and the lumbar vertebrae. The spine in this posture is curved into a well marked kyphosis which is visible externally as a hunched back. All orthopedists are agree that complete kyphosis a hunched back is an undesirable posture to hold for very long, because the increased load on the musculature supporting the head produces muscular pain in the neck and the small part of the back. The bent back encourages disc problems. For these reasons seats should be so designed that both in the forward and backward sitting posture, it should provide support to the upper edge of the pelvis and the posterior face of the sacrum. The majority of the orthopedists do not advocate a true lordosis of the lumbar region, but wish to avoid the excessive kyphosis by means of pelvic supports. This moderate aim is sensible, since prolonged maintenance of an upright seated posture with a lordosis of the lumbar spine, results in strain on the extensor muscles of the back.
The general guidelines for the design of the chair:
- The seats should be so designed so that the sitting posture is changed frequently between forward and
 backward sitting posture.
- To avoid complete kyphosis and strain on the back, the seats should be provided with a back high enough upto the shoulder blades which can make convex on the upper edge and the concave on the lower edge. This shape of the backrest keeps the back in the natural curve.
- Upright posture with a lordosis of the spinal column will quickly lead to the muscular fatigue and must be avoided for prolonged sitting.
- The height of the seat should not be more than the height of the lower leg. If in case the height is more, then legs will just above the floor and there will be static muscular contraction for the lower leg muscles, so blood supply will be stopped and there will be accumulation of lactic acid and other waste products, leading to painful fatigue.
- The depth of the seat should be equal to the length of the upper leg starting from the foremost part of the thigh
 to the knee cap.
- Width of the chair should be equal to the width of the upper thigh.
- Height of the backrest should be equal to the back from thigh to the shoulder blades with some place for the beck and the head to relax.
- It should be provided with armrest. The height of the arms should be 3” below the elbow height, similar as in case of the work surfaces.
- The backrest should be provided with a lumbar support of 8 to 14 cm. high and 10 to 15 cm. broad. It should be concave to give the spine the natural attitude. This is more convenient if the lumbar support is also adjustable.
- The optimal distribution of the force in the discs can be achieved if both the seat and the backrest are inclined backward. The angle of inclination should be from 2 to 3o.
The seats for rest and relaxation:
The people with back complaints prefer the seats for rest and relaxation with back. Profile concave forwards at the thoracic region and concave at the lumber region. A sharp backward tilt of the seat prevents forward sliding and  causes the occupant lean against the backrest with the lower part of this back and the lumbar spine. The more the seat is tilted, the more it becomes to rise from it. This point needs consideration when designing the seats for the old person.
- The easy chair should ensure that the spine is kept in its normal shape, with maximum forces on the inter vertebral discs, and the greatest possible relaxation of the back muscles.
- The most comfortable dimensions of the easy chair vary with the individual variation. Hence it is desirable that an easy chair should be adjustable in several dimensions.
- The easy chair should have backrest with a convex lumbar pad and a slight concavity at the level of the thoracic vertebral. The main supporting point the lumbar pad should be 8 to 14 cm. vertical above the seat.
- Easy chair should be well upholstered to distribute the greater part of the weight over the large area of the buttocks.
If the non-adjustable easy chair is to be designed, the following dimension should be used:
Should be used:
- Height of the seat - 39 to 41 cm.
- Depth of the seat - 47 to 48 cm.
- Slope of the seat - 20 to 20o
Seats for work: Office workers prefer to have the seat at such a height that it gives the comfortable attitude for the  upper body when working. This can be achieved when the distance between the desk top and the seat is 27 to 30 cms. Pain in the upper thigh caused when the weight of the upper back is thrown on the lower vertebrae.
- The great majority of the professional people like their work seats to be adjustable as far as possible, so that they can be fitted to whatever height users want and find most comfortable.
- The work seat must be considered in relation to the table height or desk height. The distance from the seat to the upper edge of the table should not be more than 27 to 30 cm. The distance from the seat to the underside of the desk should be at least 19 cm.
- The seat should be flat or slightly concave with the front half tilted back from 3 to 5o and the rear third building slightly upwards. The front edge of seat should be rounded off.
- The work seat must have good stability and free movement of the arms required by the users.
- The working table height or desk height recommended by most research workers is 78 cms.
- A high backrest vertically above the point of contact with the seat with a slight convex lumbar pad and slight concave at the chest height is recommended, so that the back muscles can rest maximum. It is much more preferable if the lumbar pad is adjustable both for height and width and have slight springing.
- Footrest should be available for the shorter subjects if the height of the seat is more.
- The work seat can be more comfortable if, it is upholstered on both seat and backrest in such a way that body does not sink in it more than 2 to 3 cm. The upholstery should be covered with a material that has good permeability to sweet.
- Some of the authors recommended the work table height as 78 cm, seat should be adjustable between 48 to 53 cm, depth and breadth of the seat 40 cm, height of the lumbar support 20 to 30 cm and width 30 to 37 cm.
- The most ideal work seat is one, which has the provision of adjustment, for the height, width and slop of the seat so that it can be made comfortable for forward, upright and the reclining posture.
Multi-purpose seats: Multi-purpose seats are used for a number of purposes such as table for worker, spare chair  for the living room and bed room, used for sitting in the waiting room, meeting room, restaurant and for the places of social gathering. These are mostly of light weight for the convenience of moving these and mode for the convenience of stacking.
Compromises are unavoidable in multipurpose seats that must serve the several functions and different sitting postures and are to be used for different dimensions of the people. A multi-purpose chair cannot satisfy all conditions for maximum comfort in any particular situation. For such seats where requirement cannot be forecasted, lower chairs are preferable to the higher ones.
- A pad of 2 to 4 cm of foam rubber over the whole seat is recommended.
- An ergonomic multi-purpose seat can be made more comfortable with a cushion result to wider distribution of pressure areas and also to the better resistance of the surface in slipping.
- The covering material should be permeable to air and moisture, and resistance to slip.
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