Seated Postures

In 2006, a study presented at the annual meeting of the Radiological Society of North America demonstrated the benefits of sitting with a 135° thigh-to-torso angle. Using magnetic resonance imaging (MRI), researchers showed that less strain on lumbar discs occurs in 135° sitting than in traditional 90° sitting.

Positive effects of reclined posture sitting had been shown as early as the 1970s. Gunnar Andersson used needles inserted directly into the backs of live volunteers to measure muscle activity and disc pressure in a variety of seated postures. These studies showed a reduction of low back muscle activity and disc pressure with increasing thigh-to-torso angles.

In applying the findings of the newest study, it is important to keep a few things in mind:

• It is very difficult to perform some office tasks, such as writing, in a reclined posture.
• A reclined posture puts employees further from the work surface, increasing reach requirements and visual demands.
• The 135° sitting posture shown in pictures associated with the study more closely resembles standing than sitting. Accommodating such a posture would require a height-adjustable work surface.
• The findings are based on patients with no history of back pain, and were measured at three discrete points—slouched, 90°, and 135°. No measurements were taken at intermediate data points.

Similar benefits have been demonstrated for thigh-to-torso angles as low as 110°. Increasing the thigh-to-torso angle can be achieved by:

• Manipulating the backrest and seat pan angles of an adjustable office chair.
• Use of alternative seating, such as a saddle chair, that opens the hip angle. More information can be found in State Fund’s Expert’s Corner: "New Concepts in Seating.”
• Alternating postures while performing tasks that lend themselves to a reclined posture, such as talking on the phone. No one posture should be maintained for an extended period.

When trying out new seating options or workstation arrangements, particularly those that increase thigh-to-torso angle, be sure that:

• New risk factors are not introduced.
• Avoid creating new awkward postures or increasing reach requirements.
• The feet can be supported while seated.

Revised: 04/2017