Masters of Science - Research
School of Health Sciences
Collier, Brooke, Does precision affect lifting capacity, Masters of Science - Research thesis, School of Health Sciences, University of Wollongong, 2012. http://ro.uow.edu.au/theses/3817
Within the military, soldiers perform physically demanding manual tasks, many of which involve careful or precise object placement. Precision, in terms of limb position or force during isometric single-joint contractions has been found to significantly reduce endurance capacity. However, there is a paucity of research investigating the effects of precision in terms of object placement during functional lifting tasks.
The overall aim of this thesis was to investigate the physical effects of precision on three common military task aspects: maximal lift capacity, maximal acceptable weight of lift and submaximal repetitive lifting to task failure. As one of the first studies to investigate precision during functional whole body lifting tasks, the strategies used in this thesis aim to identify or direct future research to further examine the specific mechanisms limiting precise lifting capacity.
A series of laboratory-based studies were conducted in two sections. Section One investigated the effect of precision on maximal lift capacity (Chapter 2) and maximal acceptable weight of lift (Chapter 3) at both an absolute and relative lift height, in subject cohort one. Section Two investigated the effect of precision on repetitive lift performance to task failure (Chapter 4) on subject cohort two. Physical differences between the precise and non-precise lifting conditions were assessed by muscle activity, lift duration, stance duration, rating of perceived exertion, heart rate and box control.
Three major outcomes emerged from this investigation:
i) Maximal lift capacity was reduced by 32-40% regardless of lift height when precision was required;
ii) Reductions in mass were also seen for maximal acceptable weight of lift but were observed only at an absolute lift height; and,
iii) Precision decreased repetitive lift duration to volitional task failure by 72%.
These results suggest precise object placement should be considered when analysing manual lifting tasks in the design of physical employment standard assessments within the military and other occupations. If this is not considered, a mismatch between physical capacity and task demands may arise, resulting in an increased risk of injury. Future research is required to specifically identify the mechanisms responsible for the limited capacity observed when precision is required.