Within-Subject Variability in Low Back Load in a Repetitively Performed, Mildly Constrained Lifting Task

Study Design. A repeated-measures in vivo experiment. Objective. To describe within-subject variability of spinal compression in repetitive lifting. Summary of Background Data. Epidemiology and failure mechanics suggest that peak loads may be more predictive of injury than average loads. Nevertheless, biomechanical studies usually focus on the latter. Methods. Ten healthy males performed 360 lifts in 1 hour of a 45-L crate, weighted with a stable 10-kg mass on 1 day and with an unstable mass (10 kg of water) on another day. The maximum compression force in each lift was estimated, using a simple inverse dynamics model and a single equivalent muscle model. Results. The individual distributions of maximum compression force were slightly skewed to the right (average skewness 0.67). Median and 95th percentile values were used to characterize the distribution. The median (50th percentile) compression ranged from 3375 to 6125 N, and from 3632 to 6298 N in the stable and unstable load conditions, respectively. The within-subjects peak (95th percentile) compression forces were from 405 to 1767 N and from 526 to 2216 N, respectively, higher than the median values. The peak values differed significantly between conditions, whereas the difference in medians did not reach significance. Only a limited trendwise (fatigue-related) variance could be demonstrated. Conclusion. Peak spinal compression by far exceeds median compression in repetitive lifting and can be affected by task conditions independently from the median. Therefore, the variability of spinal loads needs to be taken into consideration when analyzing and redesigning tasks that can cause spinal injuries.

[1]  S. Simon,et al.  The effect of fatigue on multijoint kinematics, coordination, and postural stability during a repetitive lifting test. , 1997, The Journal of orthopaedic and sports physical therapy.

[2]  S E Mathiassen,et al.  Quantifying variation in physical load using exposure-vs-time data. , 1991, Ergonomics.

[3]  R. Norman,et al.  A comparison of peak vs cumulative physical work exposure risk factors for the reporting of low back pain in the automotive industry. , 1998, Clinical biomechanics.

[4]  S. Kumar,et al.  Cumulative Load as a Risk Factor for Back Pain , 1990, Spine.

[5]  W S Marras,et al.  Spine loading during asymmetric lifting using one versus two hands. , 1998, Ergonomics.

[6]  Gary A. Mirka,et al.  An Investigation of the Variability in Human Performance during Sagittally Symmetric Lifting Tasks , 1996 .

[7]  J H van Dieën,et al.  Fatigue-related changes in the coordination of lifting and their effect on low back load. , 1996, Journal of motor behavior.

[8]  G D Herrin,et al.  Prediction of overexertion injuries using biomechanical and psychophysical models. , 1986, American Industrial Hygiene Association journal.

[9]  W. Marras,et al.  Variation in spinal load and trunk dynamics during repeated lifting exertions. , 1999, Clinical biomechanics.

[10]  J H van Dieën,et al.  Abdominal muscles contribute in a minor way to peak spinal compression in lifting. , 1999, Journal of biomechanics.

[11]  Stuart M. McGill,et al.  Creep response of the lumbar spine to prolonged full flexion. , 1992, Clinical biomechanics.

[12]  O G Meijer,et al.  Berstein's anti-reductionistic materialism: On the road towards a biology of activity (1965). , 2000, Motor control.

[13]  J. H. van Dieen,et al.  Towards an optimal sampling strategy of EMG and EMG spectral parameters, when using test contractions to monitor muscle fatigue , 1996 .

[14]  A. R. Lind,et al.  Metabolic, cardiovascular, and respiratory factors in the development of fatigue in lifting tasks. , 1978, Journal of applied physiology: respiratory, environmental and exercise physiology.

[15]  M Solomonow,et al.  Biomechanics of increased exposure to lumbar injury caused by cyclic loading: Part 1. Loss of reflexive muscular stabilization. , 1999, Spine.

[16]  J H van Dieën,et al.  Coordination of the leg muscles in backlift and leglift. , 1992, Journal of biomechanics.

[17]  D Chaffin,et al.  High-pass filtering to remove electrocardiographic interference from torso EMG recordings. , 1993, Clinical biomechanics.

[18]  H M Toussaint,et al.  Repetitive lifting and spinal shrinkage, effects of age and lifting technique. , 1994, Clinical biomechanics.

[19]  J H van Dieën,et al.  Stoop or squat: a review of biomechanical studies on lifting technique. , 1999, Clinical biomechanics.

[20]  W. G. Allread,et al.  The Role of Dynamic Three-Dimensional Trunk Motion in Occupationally-Related Low Back Disorders: The Effects of Workplace Factors, Trunk Position, and Trunk Motion Characteristics on Risk of Injury , 1993, Spine.

[21]  R W Norman,et al.  Effects of an anatomically detailed erector spinae model on L4/L5 disc compression and shear. , 1987, Journal of biomechanics.

[22]  Huub M. Toussaint,et al.  Evaluation of the Probability of Spinal Damage Caused by Sustained Cyclic Compression Loading , 1997, Hum. Factors.

[23]  Jaap H. van Dieën,et al.  Sensitivity of single-equivalent trunk extensor muscle models to anatomical and functional assumptions. , 1999 .

[24]  Jaap H. van Dieën,et al.  Mechanical behaviour and strength of the motion segment under compression: Implications for the evaluation of physical work load , 1994 .

[25]  W S Marras,et al.  A stochastic model of trunk muscle coactivation during trunk bending. , 1993, Spine.

[26]  J H van Dieën,et al.  Effects of repetitive lifting on kinematics: inadequate anticipatory control or adaptive changes? , 1998, Journal of motor behavior.

[27]  J H van Dieën,et al.  Asymmetric low back loading in asymmetric lifting movements is not prevented by pelvic twist. , 1998, Journal of biomechanics.

[28]  M. Nordin,et al.  1988 Volvo Award in Biomechanics: The Triaxial Coupling of Torque Generation of Trunk Muscles during Isometric Exertions and the Effect of Fatiguing Isoinertial Movements on the Motor Output and Movement Patterns , 1988, Spine.

[29]  P. Dolan,et al.  Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine. , 1998, Journal of biomechanics.

[30]  J H van Dieën,et al.  Sensitivity of single-equivalent trunk extensor muscle models to anatomical and functional assumptions. , 1999, Journal of biomechanics.