Abstract
AbstractLift‐to‐lift variability occurs in repetitive lifting tasks due to alterations in the lifting techniques used by the lifter, resulting in variability in lower back tissue loading. Understanding how trunk variability changes with time in the initial phases of a lifting bout may provide insights into the risk of injury during work startup. The purpose of this study was to quantify the variation of lifting kinematics and kinetics during the initial phase of a lifting bout. Twenty participants performed a repetitive lifting task continuously for 30 min. The load was equivalent to 10% of each participant's body weight and lifting was done at a rate of six lifts/min. Kinematic variables (three‐dimensional range of motion, angular velocity, and angular acceleration) of the trunk were measured using the Lumbar Motion Monitor and a dynamic biomechanical model estimated peak L5/S1 moment and spine compression. The variances of these variables were compared across 10‐min intervals: 0–10 min, 10–20 min, and 20–30 min. Results indicate a significant reduction in the variance of the peak sagittal acceleration, the sagittal range of motion, the transverse range of motion, peak sagittal moment, and peak spine compression between the first and second time intervals, followed by no significant change in variance between the second and third intervals. The downward trend in variation of these kinematic and kinetic variables suggests an initial adjustment period as the lifters reach a steady state of their lifting technique. The reduced variance of spinal loading may reduce the probability that a tissue tolerance is exceeded.
Highlights
Low back pain (LBP) is recognized as a significant and costly problem worldwide that impacts workers involved in occupations which require repetitive lifting exertions. Guo et al (1999) showed that LBP contributed to approximately 101.8 million days in lost productivity annually due to absenteeism from work
The purpose of this study was to quantify the variation of lifting kinematics and kinetics during the initial phase of a lifting bout
These results of the analysis of trunk kinematics illustrate that the peak sagittal acceleration, sagittal and transverse range of motion were the trunk kinematic variables that were significantly influenced by TIME (Table 1 and Figures 2 and 3)
Summary
Low back pain (LBP) is recognized as a significant and costly problem worldwide that impacts workers involved in occupations which require repetitive lifting exertions. Guo et al (1999) showed that LBP contributed to approximately 101.8 million days in lost productivity annually due to absenteeism from work. Wigglesworth (2006) evaluated data from the Australian Bureau of Statistics which showed a continuous downward trend in the percent of occupational injuries by day, with Monday contributing approximately 23% of the weekly injuries and Friday contributing 17%, with a steady downward trend connecting these two endpoints. He showed that the number of injuries peaked in the 8:30–9:30 a.m. timeframe, dropped sharply towards the middle of the work day and increased into the middle of the afternoon before falling off again towards the end of the work day While these studies did not focus exclusively on musculoskeletal disorders, but more generally on occupation injury, there appear to be some time‐related mechanisms whereby musculoskeletal disorders might contribute to these trends. These mechanisms would include end‐of‐week and end‐ of‐day effects such as muscular fatigue and cumulative trauma, as well a beginning‐of‐week and beginning‐of‐day effects such as warm‐ up effects (Woods et al, 2007), adjustment to working conditions, and so forth
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