Psychophysical and physiological study of one-handed and two-handed combined tasks
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Most psychophysical studies in manual material handling (MMH) have paid more attention to two-handed MMH activities than to one-handed MMH activities. Also, studies have been involved only with single MMH activities - lifting, lowering, carrying, holding, pushing or pulling. Some studies have examined the capacities of two-handed combined MMH activities. However, the capacities for combinations of one-handed MMH activities (lifting a box, then carrying the box, and lowering the box), especially repetitive tasks, have never been examined, although these kinds of combined one-handed tasks are very common in normal life and in industry. The objective of this study was to find the psychophysical and physiological responses of human subjects from a simulated industrial task involving one-handed and two-handed combined tasks and to develop prediction models for one-handed and two-handed combined tasks. Ten male students participated in the experiment. Capacities were determined as the maximum acceptable weight workload for a 1 hr work period 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-floor height. Individual capacities were determined psychophysically under three frequencies: six handlings per minute, one handling per minute and one handling per five minutes. In addition to the maximum acceptable weight, heart rate, tasking time and RPE values for the whole body, the arm, and the back were also measured as responses and statistically analyzed.