The Benefits of Pelvic Stabilisation
| What We Know: People are more likely to sit in upright or forward-leaning postures than to recline while working at the computer. Lumbar support alone cannot naturally restore spinal curvatures in a body that is seated in an upright position. The pelvis serves as the body’s center of mass and the primary attachment location for muscles that move the upper and lower body. When the pelvis rotates in a rearward position, the body works to restore balance at the cost of muscle fatigue and discomfort. For the purposes of studying the seated human body at work, ergonomists have identified three postures based on the location of the body’s center of mass: reclining, upright, and forward leaning (Figure 1). Because the reclined position was often observed to be the preferred posture among people seated at work, even for early users of VDTs and personal computers, (Kroemer and Grandjean 1997), work chair designers have focused their efforts on creating backrests that provide appropriately placed support and tilt mechanisms that maintain that support as the sitter moves through various postures. However, a recent study of seated behaviors undertaken by researchers at Herman Miller suggests that as a greater percentage of office work tasks are performed on the computer, people are spending a smaller percentage of time in the reclined postures that were traditionally preferred for activities such as telephoning, reading from hard copy, conversation, and even continuous keyboarding. The “Office Seating Behaviors” study found that people performing computer-related tasks used upright or forward-leaning postures nearly 75 percent of the time (Dowell, Green, and Yuan 2001). The finding is significant because each of the three postures affects the shape of the lumbar spine, or lower back, differently. The human spine (Figure 2) has four functional parts: the cervical spine (neck), the thoracic spine (trunk), the lumbar spine (lower back), and the sacrum (commonly referred to as the “tailbone”). | Because the pelvis is rigidly attached to the sacrum, and the sacrum is fixed to the lumbar spine, any rotation of the pelvis influences the shape of the lumbar spine (Chaffin and Andersson 1991), and any condition that produces a change in one of the spinal curvatures will cause compensatory changes in the other curves to maintain balance and conserve muscular energy (Rosse and Gaddum-Rosse 1997). In addition to being the location of the body’s center of mass, the pelvis serves as the attachment point for 20 major muscle groups that function to initiate movement and to counterbalance gravitational forces in both the upper and lower body (Rosse and Gaddum-Rosse 1997). When a person moves from a standing to a seated position, the pelvis tends to rotate backward, causing the lumbar spine to flatten from its natural lordotic (inwardly curved) shape or even to assume a kyphotic or outward curve (Figure 3), resulting in increased pressure on the intervertabral discs (Andersson 1974) and increased muscle activity as the body attempts to restore balance (Rosse and Gaddum-Rosse 1997). This results in increased fatigue and discomfort for the sitter over the course of the workday. Research has shown that, in reclined postures, adding lumbar support and increasing the angle between the seat and backrest of a chair allows for a natural forward rotation of the pelvis, which reduces disc pressure and muscle activity in the lower back (Andersson and Ortengren 1974). However, the effect of lumbar support is much reduced when the sitter is in an upright or forward-leaning posture (Andersson 1974). Therefore: A good work chair will promote natural, unforced, spinal alignment and muscle balance even when the sitter is not in a reclined posture. Design Problem: Develop back support that comfortably sustains the pelvis in its natural forward tilt in upright postures. For years, experts in design, ergonomics, and medicine have recognized the importance of seating design that controls the rearward tilt of the pelvis. Recent research found that the addition |