Abstract
Past research on manual load carriage has had very limited applicability to the type of load carriage which occurs in industry. The majority of studies have investigated steady continuous load carriage on the back, rather than the intermittent 'shuttle' type of carry in the arms which is more common in industry. Furthermore they have generally concentrated on the central cardiovascular or metabolic responses, and paid little attention to local muscle fatigue. The highly stylised modes of carriage used in some previous studies have also been shown to differ significantly from the more realistic freely chosen modes used in this study. This further limits their applicability. Although potentially useful, current prediction models for load carriage tasks were found to be inappropriate for intermittent carrying, and had a poor level of agreement. A need was identified therefore to develop prediction models for industrial load carriage tasks, and to make a systematic study of local muscle fatigue in load carriage. Results from the main study indicated that oxygen uptake and heart rate responses were alinear with respect to load weight, but linear with respect to distance and frequency of carry. Multiple regression analysis yielded best fit prediction equations for oxygen uptake and heart rate, based solely on inputs of load weight, carry distance, and handling frequency. The models produced are therefore relatively simple to use in practical industrial situations. They were validated experimentally and against published data. A methodology for investigating local muscle fatigue was also developed. Despite high levels of intra- and intersubject variability in response, this methodology proved useful in detecting the task conditions which were most associated with peripheral muscle fatigue. The results from these studies have indicated that when light loads are carried in the arms, whole body physiological responses adequately reflect the strain of the task. However as the load weight is increased, peripherral muscle fatigue appears to become the limiting factor. This becomes excessive in some circumstances well within current physiological stress criteria. Overall it may be better to carry light weights at a high frequency, than heavy weights at a lower frequency. This recommendation, based on a multidisciplinary study of load carriage, is at variance with the recommendations and previous studies based only on central metabolic cost criteria.