Variation in Trunk Mobility Throughout the Work Day

Abstract

Low back disorders have been a major concern for both industries and the public in general. Diurnal variation in trunk flexibility has been previously observed and quantified in terms of range of motion. It was hypothesized that decreased disc height as the day progresses allows the spinal ligaments to slacken, resulting in an increase in the range of motion (flexibility) and possible reduction in risk of injury. Evidence suggests that this risk may be accentuated under dynamic motions of the spine. This experiment focused on observing the change in dynamic components of trunk flexibility (trunk mobility) as a function of time of the day. Trunk motions of twenty-one male participants were obtained at three specific times of the day using a tri-axial electrogoniometer. No variation in trunk range of motion in any of the cardinal planes was observed. However, velocity and acceleration in the sagittal plane showed significant variations, suggesting the re-examination of the “slack ligaments” hypothesis. This study asserts that identifying flexibility by only its static component, range of motion, gives only partial information. Industrial injuries occurring in the early morning hours may be a result of insufficient trunk mobility. The relation between trunk mobility and back injury incidence rates should be further investigated.