Strength and perceived exertion in isometric and dynamic lifting with three different hand locations

Abstract

The dynamic and isometric strength and physical stress in symmetric and asymmetric lifting were measured with some common pairs of hand locations and a pair of clearly defined foot positions. In the experiment, eleven healthy male students were required to lift a small box attached to the arm of a dynamometer. The size of the box was 29 cm long, 24.5 cm wide and 23 cm high, and it weighed 10 kg. Both hands were located at three different positions on the box; the two handles near the upper edges of the box gripped with the hands (Handle type), the bottom on either side (Bottom type), and the left lower proximal corner and the right upper distal corner (Oblique type). The dynamic and isometric forces at the three hand locations were significantly different, and the least values were observed in the Oblique type irrespective of the lifting angle. Perceived exertions on the category scale (CR-10) for the left arm were very high in Oblique type lifting with any combination of height and symmetry during dynamic lifting. Therefore the burden of Oblique type lifting was thought to be greater than in the other two types of lifting, if workers are ordered to handle a box in otherwise identical conditions. In dynamic lifting Handle type lifting was thought to be the best among the three types.