Low Back Exposure Research Articles

Biomechanical differences in experts' and novices' footstep patterns during a palletizing task

Very few studies have examined differences between experts' and novices' foot positioning and movements during manual materials handling tasks. The impact of footstep patterns on low back loading needs to be better understood. The goals of this study were to characterize foot placement and movements in novices and experts and to assess their impact on back loading considering the height of grasp. The task consisted in transferring 24 15 kg boxes from a pallet to another. Foot placement and movements were classified with a recently developed taxonomy. Results show that experts' feet remained static more often than novices' feet during the lifting phase. Positioning the feet towards the deposit site during lifting increased asymmetrical moments, especially for novices. Positioning one foot forward increased asymmetrical moments for novices. Overall, footstep strategies are an effective indicator of low back exposure and should be considered in ergonomic studies.

The influence of sex and strength capacity on normalized low-back exposure during lifting: Insights from a joint power analysis

ObjectiveInvestigate the influence of sex, strength capacity, and relative load mass on low-back exposure and lower extremity joint power generation in backboard lifting. BackgroundSex and strength have been shown to influence lifting strategy, but without load mass being scaled to strength it is unknown which factor influences low-back exposures, and whether there are interactions with load mass. MethodsMotion capture and force plate data from 28 participants were collected during backboard lifting at load masses scaled to strength capacity. Differences in normalized peak low-back moment, peak knee-to-hip power magnitude ratio and timing were tested as a function of sex, strength, and load mass. ResultsStronger participants had lower normalized peak low-back moments (average 32% change from low-capacity across all load masses), with no significant sex effect (p = 0.582). As load mass increased, normalized peak low-back moment, peak knee-to-hip power magnitude and synchronicity decreased. ConclusionTraining to both increase strength capacity and hip-joint power generation may be a strategy to reduce low-back exposure in backboard lifting.

Understanding individual differences in lifting mechanics: Do some people adopt motor control strategies that minimize biomechanical exposure.

The movement strategy an individual uses to complete a lift can influence the resultant biomechanical exposure on their low back. We hypothesize that some lifters may choose a motor control strategy to minimize exposure to the low back, where others may not. Lower magnitudes of exposure to the low back coupled with less variability in lift-to-lift exposure and in features of movement strategy related to biomechanical exposure would support that such lifters consider minimizing exposure in their motor control strategy. We tested this hypothesis by investigating if differences in variability of low back exposure measures, as well as features of movement strategy related to resultant low back exposures differed across lifters. Twenty-eight healthy adults participated in the study where ten repetitions of a lifting task with the load scaled to 75% of participant's one-repetition maximum were completed. In all trials, whole-body kinematics and ground reaction forces were collected. Lifters were grouped as low, moderate or high relative exposure based on low back flexion angles and normalized L4/L5 extensor moments when lifting. Principal component analysis was used to identify independent movement strategy features, and statistical testing determined which features differed between high and low exposure lifts. Variability in low back exposures and movement features associated with relative biomechanical exposure were compared across lifter classifications. Significantly less variability was observed in low back exposures among the low exposure lifter group. Additionally, a trend towards lower variability in movement features associated with relative biomechanical exposure was also observed in low exposure lifters. These findings provide initial support for the hypothesis that some lifters likely define a motor control strategy that considers minimizing biomechanical exposure in addition to completing the lift demands. Future work should explore how state and trait-based factors influence an individual to consider biomechanical exposure within their motor control strategy in lifting.

Development and validation of an easy-to-use risk assessment tool for cumulative low back loading: The Lifting Fatigue Failure Tool (LiFFT)

Recent evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in affected tissues. This paper describes a new low back exposure assessment tool (the Lifting Fatigue Failure Tool [LiFFT]), which estimates a “daily dose” of cumulative loading on the low back using fatigue failure principles. Only three variables are necessary to derive the cumulative load associated with a lifting task: the weight of the load, the maximum horizontal distance from the spine to the load, and the number of repetitions for tasks performed during the workday. The new tool was validated using two existing epidemiological databases: the Lumbar Motion Monitor (LMM) database, and a database from a U.S. automotive manufacturer. The LiFFT cumulative damage metric explained 92% of the deviance in low back disorders (LBDs) in the LMM database and 72–95% of the deviance in low back outcomes in the automotive database (depending on the outcome measure). Thus, LiFFT is practitioner friendly and its cumulative damage metric highly related to low back outcomes.

The Low Back Cumulative Trauma Index

Recent evidence strongly suggests that force and repetition interact in a consistent manner to affect the risk of musculoskeletal disorders (MSDs), likely due to an underlying fatigue failure process in affected tissues. However, no MSD tools to date have been based on fatigue failure theory. The present proposal describes a basis for incorporating fatigue failure theory in a new low back exposure assessment tool: the Low Back Cumulative Trauma Index (LBCTI), and provides an illustration of the effectiveness of such an approach using an existing database on low back disorder (LBD) risk. The LBCTI demonstrated a dose-response relationship to LBD risk.

The accuracy of self-report and trained observer methods for obtaining estimates of peak load information during industrial work

The purpose of this study was to determine how well self-report (questionnaire=QR) and trained observer (checklist=OBS) data recording methods compared with more expensive video analysis (VID) for estimating various peak physical loading exposure variables on the low backs of 99 employees during work in an automobile assembly plant. The variables studied were L4/L5 spine compression and shear forces, L4/L5 moment, trunk angle, and hand load. Peak low back loads associated with the working postures of, and the applied loads on, each worker were estimated using a 2D biomechanical model that could accommodate inertial forces acting in various directions on the hands independently. Correlations between the VID and OBS methods were greater for each variable than between VID and QR methods, with ranges in coefficients from 0.6 to 0.8, and 0.1 to 0.4, respectively, giving a discouraging impression of the QR, and the OBS method to a lesser degree, for peak low back exposure assessment. Despite the better performance of OBS method for individuals, it was still only able to account for between 36% and 64% of the variance relative to the VID method. When all workers were considered as a single group, compression and shear forces, moment and hand load estimates were the same regardless of method used to collect the data. Self-reported trunk flexion was significantly greater than that reported by trained observers or on video ( p<0.0001). Relevance to industry Considerable time and expense could be saved in large scale studies if it were possible to rely on worker's reports or observation of the physical demands of their jobs instead of traditional video and biomechanical analyses. Assessments of peak exposure of individuals using the self-report and observation methods were discouraging. Analysis of a single group proved more promising, but other groups need to be studied. Interview assisted self-reports may help to improve assessments of individuals and also need to be investigated in the future.