Research Review: Research on effects of standing to low back pain risk
By Shawn ThistleFeatures Research
Studies of asymptomatic individuals with no lifetime history of low back pain (LBP) have indicated that 40 to 70 per cent report clinically significant LBP after a two-hour standing protocol. This induced (but transient) LBP paradigm has allowed characterization of neuromuscular differences between individuals who develop LBP when standing compared with those who do not.
Study #1. Gallagher KM, Campbell T, Callaghan JP. “The influence of a seated break on prolonged standing induced low back pain development.” Ergonomics 2014; 57(4): 555–562
Study #2. Nelson-Wong E, Callaghan JP. “Transient low back pain development during standing predicts future clinical low back pain in previously asymptomatic individuals.” Spine 2014; 39(6): E379 – E383.
Studies of asymptomatic individuals with no lifetime history of low back pain (LBP) have indicated that 40 to 70 per cent report clinically significant LBP after a two-hour standing protocol. This induced (but transient) LBP paradigm has allowed characterization of neuromuscular differences between individuals who develop LBP when standing compared with those who do not. The purpose of one study summarized here (#2 listed above) was to determine the effect of prolonged standing on the long-term rate of LBP in previously asymptomatic individuals.
This review summarizes the results of that, and an additional study from the same author group, investigating the biomechanics of LBP and the effect of standing, both during work and for prolonged periods, as causative and predictive indicators of LBP.
Of 20 participants, 55 per cent were identified as pain developers (PD) based on their visual analog scale (VAS), demonstrating a steady increase in reported LBP over the first 45 minutes of standing. LBP decreased during a 15-minute seated break, but increased to a higher level following a second 45-minute standing period.
Participants recorded baseline VAS upon entering the laboratory and following outfitting with accelerometers. Desk height for each participant in both seated and standing position was measured and set on an adjustable workstation. Working position was established using ergonomic standards (desk height slightly below elbow height, top of computer monitor at eye level). Participants completed typical computer work (typing, mouse and combination) for 45 minutes, followed by a 15 minute break. This pattern was repeated twice (total time: 2 hours).
Participants were categorized as pain-developers (PD) if their VAS score changed by 10mm or more in one of the standing trials. Outcome measures were entered into a three-way general linear model with between factors of gender and pain group (PD/non-PD) and a within factor of time. The level of significance was set at p < 0.05.
An interaction between time and pain group was found for the median thoracic angle of the amplitude probability distribution function (APDF) (p = 0.0039). During standing, non-PDs demonstrated greater thoracic flexion, differing by approximately eight degrees in the first 45 minutes of standing. During sitting, PDs demonstrated an increase of the median thoracic angle of approximately 10 degrees, while non-PDs remained consistent in both sitting and standing.
A main effect of time was found for thoracic angle range. The thoracic range for both PDs and non-PDs increased during the first 45-minute standing period, continued to increase through the 15-minute rest period and remained elevated following the second standing and sitting phases.
Main effects of pain group (p = 0.0091) and time (p = 0.0405) were found for lumbar spine range of motion. Overall, non-PDs utilized a greater range of their lumbar spine angle compared to PDs.
• A convenience sample of university students was used, which may not provide for extrapolation to the general working population,
• LBP was subjectively reported by participants, and
• No orthopaedic or neurological testing was utilized.
• The workstation was suitably adjustable and recreated a real-world workstation, and
• The use of accelerometers allowed for accurate measurement of lumbar and thoracic angles.
Forty-three participants aged 18 to 50 were recruited from the University of Waterloo in Ontario and surrounding communities. Seventeen participants were classified as PDs – with demonstrated 10-mm or more increase on the VAS during standing exposure – the remaining 26 were non-PDs.
Participants recorded baseline VAS upon entering the laboratory. They were then positioned at a standing work surface and instructed to “stand as they normally would if they were waiting in line or standing at a counter”. Participants were given tasks to perform that simulated light occupational assembly duties. Participants remained standing for a period of 2 hours, recording VAS at 15 minute intervals.
Participants were invited to complete an annual questionnaire about the LBP status during the next 36 months. The goal of the questionnaire was only to ascertain whether an individual had experienced an episode of nontraumatic clinical LBP that required treatment by a health care professional within the prior 12-month period.
Independent t tests were used to compare PD and non-PD group characteristics at baseline to show equivalence in demographic factors. Chi-squared tests were used to determine equivalence in sex distributions between groups.
For 36 months, a higher proportion of PD participants reported at least one episode of LBP severe enough to seek medical care or that resulted in three days missed work, school or recreational activities. Three PDs and one non-PD reported more than one episode of LBP. None of these episodes were associated with trauma.
LBP developed during prolonged standing was the strongest predictor of future LBP during the first 12 months. Individuals classified as PD during prolonged standing developed LBP at a rate three times that of non-PD during the first 24 months of the study.
Although a greater proportion of PDs developed LBP as compared with non-PDs, 23.1 per cent of non-PDs nonetheless developed LBP. The resulting poor findings for negative likelihood ratios and sensitivity indicate that LBP during prolonged standing may not be a good screening tool for future pain as many individuals who did not report LBP during standing went on to experience clinical LBP.
At 36 months, a greater percentage of PD reported multiple episodes of LBP than non-PD, which may indicate PDs are more likely to transition to chronic LBP. LBP during prolonged standing may be valuable in identifying individuals prone to developing chronic LBP.
• The small sample size limits the ability to extrapolate the findings to a larger population,
• Follow-up interviews did not provide substantive information regarding the details of subsequent LBP or identify confounding factors, and
• Information about LBP episodes was based on self-reporting and therefore is subject to recall bias.
• The workstation used was suitably adjustable and recreated a real-world workstation, and
• The use of motion capture technology and EMG allowed for accurate measurement of mobility and muscular activity.
Standing posture is associated with significant biomechanical actions and can itself be a causative factor for low back pain. The two studies summarized here suggest that standing in the workplace may be causative for LBP. A seated break following periods of standing did not, however, mitigate LBP in study participants. Similarly, in asymptomatic individuals with no history of low back pain, it was observed that development of low back pain during prolonged standing could be a predictor for development of chronic low back problems.
The combined results indicate that clinicians should consider LBP during prolonged standing as a potential screening tool to help identify “pre-clinical” LBP and caution patients from adopting a standing workstation.
Dr. Shawn Thistle is the founder and CEO of RRS Education (rrseducation.com), which helps busy clinicians integrate current research evidence rationally into practice. He also maintains a practice in Toronto, lectures at CMCC and provides chiropractic medicolegal consulting services. Reach him at: email@example.com
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