Psychophysical and physiological study of one-handed and two-handed combined tasks

Most studies in manual material handling (MMH) have paid attention to singl e MMH activities - lifting, lowering, carrying, holding, pushing or pulling and have ignored combined activities. Also, most studies have involved two -handed (symmetric) MMH activities rather than one-handed MMH activities. V ery few studies have reported information on workers' capacities for combin ations of one-handed MMH activities (e.g. lifting a box, then carrying the box, and lowering the box). These kinds of combined activities are common i n industry and in our daily lives. The objective of this study was to utili ze the psychophysical approach to examine the combinations of lifting carry ing and lowering activities from a simulated industrial task involving one- handed and two-handed combined tasks, and to develop mathematical models fo r combined tasks. Ten male students served as subjects for the study. Maxim um acceptable weight workload capacities for Ih work periods for one-handed and two-handed combined tasks (lifting a box from floor-to-knuckle height, carrying the box for 4.3 m, and lowering the box from knuckle-to-poor heig ht) were determined psychophysically under three frequencies: six handlings per minute, one handling per minute, and one handling per 5 min. In additi on to maximum acceptable weight, heart rate, ratings of perceived exertion (RPE) values and tasking time were also measured as response variables. Com bined MMH capacity models for one-hand and two-handed tasks were developed. The advantages and disadvantages of different models are discussed.