Competition in industry has resulted in a reduction in the workforce. To maintain production rate, tasks have been added to existing jobs resulting in longer work durations and shorter recovery pauses. Recovery pauses of 20-35 seconds in a work cycle of one minute in one large automobile industry are being reduced to five seconds so that individuals work 55 seconds per minute. The purpose of this thesis was to improve the understanding of the effects of a “55/5 second minute” o f a simulated industrial “light” assembly task on the magnitude of risk factors which have been proven or proposed to be related to the reporting of low back pain. This thesis consists of four linked studies all addressing reductions in recovery time during a cyclic “light” assembly task.

In all four studies the same assembly task was performed which involved alternation between work with the trunk flexed forward 30° and recovery in upright standing within a one minute cycle. The task involved essentially zero external forces on the hands and in most plants would be considered to be a low loading job. Proven and proposed risk factors for low back pain reporting were measured;​ peak and cumulative spinal loading, perceived discomfort, muscular activation levels and local muscular fatigue. Trunk angle and lumbar spinal curvature were measured to evaluate alterations in work posture.

The first study was done to improve the understanding of an increase in work/recovery ratio of a “light” assembly task on the magnitude of risk factors. Nine female university students performed the assembly task with a fixed lordotic lumbar curvature at work/recovery ratios of 25/35,40/20 and 55/5 seconds on three separate days, each for a duration of 25 minutes. An increase in work/recovery ratio was hypothesized to increase the magnitude of risk factors. Cumulative spinal loading, local muscular fatigue and ratings of perceived discomfort increased with increasingly more adverse work/recovery ratios.

Reduction of the magnitude of risk factors, by changing lumbar curvature from a fixed lordotic to a fixed flexed curvature, during a “55/5 second minute” of “light” assembly was addressed in the second study. Nine female university students performed the assembly task for 25 minutes in either a fixed lordotic or a fixed flexed lumbar curvature, which was hypothesized to reduce discomfort. Participants found both lumbar curvatures equally uncomfortable and painful.

The third study addressed the effects of a self-selected lumbar curvature on the magnitude of risk factors. Ten experienced assembly workers and five inexperienced participants performed the assembly task for one hour. On average, the self-selected curvature resulted in lower perceived discomfort, as was hypothesized, even after a full hour of task duration compared to 25 minutes of assembly in a fixed lordotic or fixed flexed curvature.

The responses during “light” assembly of individuals who had recently had low back pain compared to those who had not had low back pain were addressed in the forth study. Nine women who had recently had low back pain were recruited and it was hypothesized that they would alter trunk posture and lumbar curvature to alleviate discomfort and pain. After one hour of the assembly task, the individuals who had had low back pain did not alter trunk angle or lumbar curvature more than those who had not had low back pain. This might be explained by the similarity in discomfort ratings between the groups.

Whether ratings of perceived discomfort can replace instrumented measures of risk factors was addressed following the series of studies. Average ratings of perceived discomfort could replace instrumented measures when evaluating various situations of “light” assembly work that differed substantially in the magnitude of risk factors. However, perceived discomfort was not related to instrumented measures of risk factors when evaluating one and the same work situation. It is not clear on which risk factors individuals base their perceptions of discomfort. Therefore, when evaluating one work situation of “light” assembly, ratings of perceived discomfort can not replace instrumented measures of risk factors. They appear to be measuring different phenomena.

From this work it was concluded that the type of “light” assembly work done in this study during a “55/5 second minute” was not light in terms of cumulative spinal loading, local muscular fatigue and perceived discomfort. Use of the “55/5 second minute” during “light” assembly is not recommended and individuals should be encouraged to adopt a self-selected lumbar curvature. The introduction of changes in trunk posture, in flexion-extension, might induce postural relief.