Maximum frequency acceptable to female workers for one-handed lifts in the horizontal plane

Abstract

A laboratory study was conducted to determine the maximum frequencies acceptable to female workers for one-handed lifts in the horizontal plane. A psychophysical method was used to determine maximum acceptable frequency for an 8-hour workday. Ten female college students were required to lift continuously three different loads to two different reach distances (38 and 63 cm) on a 91 cm high work table. The lifting task was paced by a repeating timer which the subject controlled according to her subjective feelings of fatigue. Heart rate and RPE were measured during the last 5min of the experiment to determine the physiological level of functioning and perceived exertion. Psychophysically determined maximum acceptable frequencies were compared with the standards based on methods-time measurement (MTM) analysis.

Statistical analysis showed that both the weight of the load and reach distance had a significant effect on maximum frequency acceptable to the subjects. No single value for percentage of maximum frequency can be used to establish permissible one-handed lift limits in women; rather, this value depends upon the weight of the object and distance of lift. The average maximum acceptable frequency was 51% of the maximum frequency that the subjects could maintain for a period of 4min. The subjects selected workloads which resulted in a mean heart rate of 101 beats/min. The subjects rated the perceived exertion ranging from ‘fairly light’ to ‘somewhat hard’. Performance based on MTM analysis ranged from 11% below to 32% above the maximum workload acceptable to the subjects. The non-significant heart rate differences found among the six load-distance combinations lend strong support for the use of psychophysical methodology in future studies of fatigue criteria. The study also supports the previous findings that separate physiological fatigue criteria are needed for tasks involving arm work and whole body exertion.