Posture Research

5.1. Bridger R., Von Eisenhart-Rothe C., Henneberg M. Effects of Seat Slope and Hip Flexion on Spinal Angles. Human Factors 1989; 31(6): 679-688.

In this study the lumbar spine (lower back) and thoracic spine (mid-back) curves of 25 men and 25 women were measured in four different sitting postures, including A) a flat seat bottom and a 90 degree sitting angle (called “trunk / thigh angle”), B) a flat seat bottom and a slightly more open 65 degree trunk / thigh angle, C) a 15 degree forward sloped seat bottom and a 90 degree trunk / thigh angle, and D) a 15 degree forward sloped seat bottom and a 65 degree trunk / thigh angle. The lumbar lordosis (lower back inward arch) and the thoracic kyphosis (mid-back outward arch) both measured less with the flat seat bottom and a 90 degree trunk / thigh angle, and measured more with the 15 degree forward sloped seat bottom and a 65 degree trunk / thigh angle. The authors concluded that forward pelvic tilting caused by sloping the seat bottom and / or opening the trunk / thigh angle is directly related to greater lumbar lordosis (lower back arch). Chair design could prevent backward tilting of the pelvis, which decreases lumbar lordosis (flattens the lower back arch), by sloping the seat bottom and opening the trunk / thigh angle.

5.2. Rempel D., Wang P., Janowitz P., Harrison R., Yu F, Ritz B. A Randomized Controlled Trial Evaluating the Effects of New Task Chairs on Shoulder and Neck Pain Among Sewing Machine Operators. Spine 2007; 32(9): 931-938.

In this study 247 sewing machine operators were subjected to a randomized controlled trial to evaluate the effect of chair design on neck/shoulder pain, as this population of workers has a high prevalence of upper body discomfort. The workers were divided into three groups 1) control group that received various items such as a footrest, table-top storage box, side table, task lamp, and reading glasses, 2) intervention group that received the various items plus a chair with a curved seat bottom, and 3) an intervention group that received the various items plus a chair with a flat seat bottom. After the interventions started the group of workers were re-evaluated (using symptom questionnaires) at one-month intervals over a four month period. The pain scores for the control group and the intervention group with the flat seat bottom worsened while the pain scores for the intervention group with the curved seat bottom improved during the follow-up period. The author of the study concluded that these workers may experience a decline in neck/shoulder pain if they are provided an adjustable chair with a curved seat bottom.

5.3. Saarini L., Nygard C., Rimpela A., Nummi T., Kaukiainen A. The Working Postures Among Schoolchildren – A Controlled Intervention Study on the Effects of Newly Designed Workstations. Journal of School Health 2007; 77(5): 240-247.

The aim of this study was to investigate the effects of individually adjustable saddle-type chairs with wheels, and desks with contoured front edge, tilted top, and arm support, on schoolchildren’s working postures. Pre and post measurements of posture on 97 sixth and eighth grade schoolchildren at two different schools were taken over a one-year period. One school (the intervention group)had the new design chairs and desks while the other school (the control group) had conventional school chairs and desks. The idea was that the newly designed workstations, compared to the conventional ones, would increase or open the trunk-thigh angle (the angle between the torso and upper leg) during sitting and thus improve back and neck upright posture. Each workstation was adjusted as optimally as possible to match the size of each child and was readjusted periodically throughout the study period to ensure a proper fit. The authors of this study claimed they achieved a significant increase in upright back and neck postures in the group of children using the saddle-type chairs with wheels, and desks with contoured front edge, tilted top, and arm support.

Comments:

The statistics used in this study to validate the outcome of improved postures are somewhat convoluted and difficult to understand. For example, the authors stated that “the new workstations failed to bring about better sitting posture among all participants, instead, some postures deteriorated during the follow-up period...” That doesn't sound like improved postures. Maybe what happened was that the intervention group's posture deteriorated less than the control group's posture. Nevertheless, this study has some important lessons to learn about behaviors. The authors quoted some research in their literature review section that stated new school workstations did not affect children’s actual sitting behavior and they emphasized the need for proper instructions to achieve better working postures —as ergonomic workstations alone do not seem to improve sitting habits. The authors also brought up the possibility that the additional instructions (and added attention and repeated follow-up) on optimal sitting posture given to the schoolchildren in the intervention group might have helped to improve the postures as compared to the schoolchildren in the control group that received no such instructions. Therefore, it would be hard to know if improved postures (or less bad postures) were the result of the new workstations, the increased attention to posture, or maybe both. I think the important message here is that ergonomic equipment implemented without proper instruction and greater attention to posture on an on-going basis cannot be expected to improve posture outcomes.