Epidemiologic evidence supporting optimal seating is limited and inconsistent. This cross-sectional study was conducted to examine the association between seat inclination, use of lumbar support, and the prevalence of clinically significant low-back pain among taxi drivers
A digital inclinometer was used to measure inclinations of seat surfaces (theta(seat)) and backrests (theta(back)), and calculate the back-to-thigh angle (theta(back-thigh)). Structured interviews were conducted to gather information on the use of lumbar support and the prevalence of low-back pain that had led to medical attention or absence from driving in the past month. A multiple logistic regression analysis was used to estimate the prevalence odds ratio (OR) with adjustment for age, body mass index, professional seniority, monthly driving hours, and the intensity of exposure to whole-body vibration.
Among 224 drivers, the mean theta(seat), and theta(backrest) were 14.5 (SD 9.6) and 95.1 (SD 2.7) degrees, respectively, resulting in theta(back-thigh) of 80.6 (SD 9.3) degrees. Fifty-five percent used a lumbar support regularly, but 25% reportedly had significant low-back pain. The prevalence of low-back pain was 23% among those with theta(back-thigh) 91 degrees. The adjusted OR comparing those with a theta(back-thigh) of < or = 91 degrees to those with a theta(back-thigh) of >91 degrees was 5.11 [95% confidence interval (95% CI) 1.07 approximately 24.4]. For regularly using drivers versus those not using lumbar support, the prevalence of low-back pain was 18% versus 34%, with an adjusted OR of 0.33 (95% CI 0.16 approximately 0.68). Neither theta(seat) nor theta(backrest) alone was significantly associated with low-back pain.
The epidemiologic observation of this study was consistent with the results of prior biomechanical studies on appropriate seat inclinations and the use of lumbar support. Prospective studies are needed to confirm the true beneficial effects of these seating parameters.
This study was half as I would have expected and half new to me. Taxi drivers who used a lumbar support were less likely to have low back pain than those who did not (18%, vs 34%). This is in line with Stuart McGill’s study on lumbar supports lessening low back pain in airline seats, and is immediately obvious when someone with low back pain and a bad seat adds the right size lumbar support. What was new to me was that neither seat angle nor backrest angle were individually related to low back pain, while together they were. Drivers were less likely to have pain if the angle between the seat and backrest was greater than 91 degrees (9% vs 23-37% in those with a lesser angle). For example, if your seat were declined rearward 10 degrees (from horizontal) , then the backrest would need to be reclined greater than 102 degrees from horizontal such that the drivers thigh to torso angle would be greater than 91 degrees (making an obtuse rather than acute angle). Alternatively: if the seat was perfectly level, the backrest of the seat would only need to be reclined a 91 degrees in order for the driver’s thigh and torso to form the appropriate angle.
So the take home is lumbar supports do decrease low back pain, as does having seat to backrest angle being at least 91 degrees. Seat position though is a bit of a tradeoff. I frequently caution against reclining the backrest too much as it sometimes forces people to excessively reach forward for the steering wheel, which puts more stress on the neck, shoulder, and eventually the low back again. As such, when providing physical therapy treatment for low back or neck pain it’s worth taking a look at car or truck seat position to make adjustments to decrease stress on the spine. The patient can then make similar seating adjustments at work and home to further decrease static stress on the spine.
As always, if you have any further questions or need for clarifications, please don’t hesitate to ask. Being aware that some of my blog ideas are contentious and occasionally a bit out of the field of my expertise, I encourage my readers to come forth with any questions/comments that are of interest or concern. Your comments are valued and welcomed.
Chad Reilly is a licensed physical therapist, located in North Phoenix, practicing science based medicine with treatment protocols unique and effective enough to proudly serve patients from Phoenix, Scottsdale, Mesa, Chandler, Tempe, Peoria, and Glendale.