Psychophysical modeling of manual materials-handling capacities using isoinertial strength variables

Strength testing has been used to determine a worker's physical capacity as well as to screen an individual for placement in future employment. A comparison is made of the relationships between two types of strength tests (isometric and isoinertial) and the manual materials-handling (MMH) capacities of individuals. Four MMH activities were evaluated: lifting from floor to knuckle height, lifting from knuckle to shoulder height, lowering from knuckle to floor height, and carrying for a 4.3-m distance. Psychophysical capacities were determined under three frequency conditions: one-time maximum, 1 lift/min, and 6 lifts/min. Isoinertial 1.83-m maximum strength (T1), tested on the incremental weight-lifting machine, proved to be the most highly correlated strength test to the capacities for MMH activities. Second-order polynomial regression models for MMH capacities were developed using T1 as a predictor. The isoinertial strength test T1 is recommended as the most promising single screening test because of its simplicity and task similarity.