Supine postural positions were less comfortable than upright or tilted postures for low back pain-suffering computer operators who performed short duration keyboarding tasks in a Georgia based study. Also, supine postural positions were found to be less comfortable through the upper extremity among both low back pain/non low back pain suffering subjects.
Reduced keyboarding speed was associated with the supine postural positions compared to upright, tilted, and reclined postures. However, the greatest mean typing speed difference among the five tested postures was a little more than 3 words per minute – relatively small for most office tasks.
Keyboarding accuracy was not significantly affected by postural position.
Study Design
The study involved 26 volunteers who were classified as having no low back pain (8), slow onset low back pain (10) and quick onset low back pain (8). There was no statistical difference between these three groups as to age, height, and weight. All subjects were touch typists.
Experiment Equipment
A Position Dynamics Optima tilt/recline wheelchair was mounted to a fixed base. A straight keyboard and wireless trackball mouse were used on an adjustable keyboard tray secured to the wheelchair armrests. Supported on an independent frame, a 17 inch monitor could be adjusted over a vertical height distance from 100 to 180 cm and monitor angle from 90º (upright) to 0º (parallel to the floor).
Experiment Procedure
The subjects were randomly placed in one of five seated postural positions (upright, tilted, reclined, supine1, and supine 2). The footrest, keyboard, armrests, and monitor were adjusted to fit/support the volunteer.
Three five-minute typing trials were performed by the subject with instructions to keyboard at a comfortable pace with a concentration on accuracy. After finishing a five-minute typing trial, a body part discomfort survey was completed. An overall comfort rating was given by the subject for the seated postural position at the conclusion of the three five-minute typing trials.
Once the typing trials for one postural position were completed, the subject was randomly placed/tested in one of the other seated positions until all five postures were tested.
Key Metrics
The dependent variables measured in this study were:
- typing speed
- typing accuracy
- overall comfort rating
- body part discomfort rating
Study Limitations and Concerns
This study was approached from the perspective that a supine position would reduce pressure on low back disc and potentially lessen low back symptoms. However, the authors point out that there are many non-disc related low back pain conditions that a reclined postural position may not benefit.
Further, the authors note that study conclusions are based on the performance of three five-minute typing trials. A longer test time period (the same trials performed periodically over a three-month period) may allow subjects to become more comfortable with the extreme postures (supine) when keyboarding and produce different findings.
The lumbar support of the wheelchair was not described. The nature and adjustability of the lumbar support may have influenced subject low back comfort.
The Bottom Line – How This Applies To Ergonomists
When working with an office worker who suffers from low back pain, it is prudent to investigate the impact of various sitting postures on lumbar spine symptoms. Case by case evaluation will likely yield the best outcome.
Although varying postural position is considered desirable in office ergonomics, the value of assuming a supine position while performing short duration keyboarding tasks is elusive.
Article Title: Impact of seating posture on user comfort and typing performance for people with chronic low back pain
Publication: International Journal of Industrial Ergonomics, 38, 35-46, 2008
Authors: S Haynes and K Williams
This article originally appeared in The Ergonomics Report™ on 2008-05-07.