Reposition sense of lumbar curvature with flexed and asymmetric lifting postures

Abstract

Study design: Reposition sense of lumbar curvature was assessed as a function of trunk flexion, trunk asymmetry, and target lumbar curvature using a repeated-measures design and an active-active proprioception paradigm.

Objective: The objectives of the research were to measure the ability of the subjects to sense and control the lumbar curvature in different lifting postures and to see if error in the lumbar curvature would increase in high-risk postures.

Summary of background data: The risk of low back disorders (LBDs) is related to trunk posture, with greater risk reported in flexed and asymmetric trunk positions. Spinal posture, including trunk position and lumbar lordosis, influences spinal stability. Hence, the ability to accurately sense and control spinal curvature may be an important factor in the control of LBD risk.

Methods: Eleven subjects were trained to assume specified lumbar curvatures using visual feedback. The ability of the subjects to reproduce this curvature without feedback was then assessed. This procedure was repeated for different trunk postures, including flexion and asymmetry, and with different target lumbar curvatures.

Results: These measurements demonstrated reposition error was increased in flexed trunk positions but was unchanged with trunk asymmetry. This increase in reposition error with flexion was diminished when the target posture and lumbar curvature were highly flexed and kyphotic.

Conclusions: This research suggests that it may be difficult to control spinal curvature in flexed positions, leading to an increased risk of injury. For jobs in which flexed working postures are unavoidable, therefore, it is important to minimize potentially unstable events such as slipping or shifting loads to avoid injury.

Figures

Figure 1

Torso angle (twist, lateral bend, and flexion) is the tilt of the torso from horizontal as defined by the position of the three markers (A). Lumbar curvature is the difference in angle in twist, lateral bending, and flexion of the marker at T10 relative to the marker at S1 (B).

Figure 2

Visual feedback was accomplished by displaying trunk posture (graph on right) and lumbar curvature (bars on left) in a display similar to that illustrated here. Trunk posture was represented on an x-y graph, with the x-axis as twist and the y-axis as flexion. Subjects matched a circle (representing their position) to a square (representing the target). For lumbar curvature, subjects matched the right bar plot (representing their lumbar curvature) with the left bar plot (representing the target). The lumbar curvature display was turned off for reposition sense testing.

Figure 3

Error (in degrees) in training run tests was calculated as the absolute difference between the target lumbar curvature (displayed for the subject) and the actual lumbar curvature. This error did not change significantly with flexion or asymmetric (twist). A, The error at a flexion angle of 0°; B, the error at a flexion angle of 30°; and C, the error at a flexion angle of 60°.

Figure 4

Error (in degrees) in position sense tests was calculated as the absolute difference between the target lumbar curvature (not displayed) and the actual lumbar curvature. A, The error at a flexion angle of 0°; B, the error at a flexion angle of 30°; and C, the error at a flexion angle of 60°. This error increased significantly at flexion angles of 30° (B) and 60° (C). However, the error did not change with asymmetric (twist). In the fully flexed kyphotic posture, error was reduced.