4

• Disc pressures also change dramatically when a person moves among standing, upright and slouched seated postures. Disc pressure is greater during sitting than standing and disc pressures drop with an inclination of chair backrest, especially when it is tilted from vertical to 110 degrees.
• The lumbar padding reduces the spine pressure
• Maintaining a good sitting posture can not only help to improve appearance but it can also alleviate pain in the neck and back.
• Forward posture: centre of mass in front of the ischial tuberosity. Floor supports more than 25% of body weight. Common posture for desk work.
• The classic upright seated position with perfect 90 degree torso angles is acceptable, but rarely used.
• Reclined Posture: Centre of mass behind ischial tuberosity. Floor supports less than 25% of body weight. Common for chairs with large, inclined, backrest. Preferred for resting
• • Although this posture reduces the pressure on the discs, it is not necessarily functional for working because it also increases viewing distance and arm reach to the work area.
• Sitting is more efficient way to perform many occupational and non occupational task.
• Sitting in many jobs makes good sense, as it relieves the body’s supporting muscles, offers them a chance to rest, and is less demanding on the blood circulation to the legs.
• Seat Waterfall: The seat design slopes slightly downward to relieve the pressure on the back of the thighs
• Seat Pressure: offers increased support and comfort to relieve pressure behind the knees and improve blood circulation to the lower limbs.
•  Chairs have features such as:

   Adjustability

   Seat height range

   Backrest

   Wrist rest

   Seat depth

   Stability
• Biomechanics measure: to either relieve the force or to distribute the force over larger surfaces.
• Seated manual tasks should be designed to maintain vertical alignment of the spine, and avoid constant stress on the shoulder region. T
• vertical alignment of the spine, and avoid constant stress on the shoulder region. This alignment can be done by:

   providing materials at or slightly below elbow height

   Providing arm rests where appropriate

   providing tool balancers and avoid heavy hand tools

   avoiding tasks that require the shoulder or arms to be excessively high (keep below 15 cm above the surface of the work surface)
• Reaching Zones

  primary zone – immediate reach, for items needed most frequently or of highest importance
• Reaching Zones

  secondary zone – within arm’s reach, for items of lower importance or used occasionally
• Reaching Zones

  tertiary zone – area farthest away which requires you to bend forward to reach, for rarely used items
• More workers are injured using a computer keyboard in the US than any other tool for the workplace!
• Wrist pad distributes the force and reduces the pressure on the wrist.
• Active breaks should be done every 15 minutes, specially for typists who work more that 3-4 hr with their computer.
• Factors influencing monitor’s height

   Tasks  Accuracy  Glasses  Space needed
• -        We like to slouch because when we sit up straight, we have to use erector muscles and we get tired and want to relax. When you slouch you are not having an active erector muscle. The pressure is now shifted onto your discs
• -        When you stay static too long you loose blood flow because the muscle holds onto the blood that is inside the tissue. The blood loses oxygen because there is a lack of oxygen exchange and no acid is removed
• -        Gym ball chairs are not safe unless they have legs or back support and once you do that it loses the gym ball affect
• -        These split keyboards are used for people who type all day for a living a non-split key board really should not be used for more than 90-120 minutes
• -        Again, for wrist support you want the wrist to be straight you do not want it at an angle. The mouse also should not deviate the wrist