Work and energy transfers in maximal pushing of loads

Abstract

The costs related with manual work injuries produced by excessive pushing activities are impressive and therefore the biomechanical study appears to be very relevant. Six male subjects were evaluated for work-energy factors and maximal muscular moments at all body joints when performing four maximal pushing tasks at waist level. In the first three experimental tasks the number of segments participating in the tasks was increased from the minimal technique (upper limbs only), to the intermediary technique (trunk and upper limbs only) to the complete technique (all segments). In addition, these segments were set into motion in the same angular direction in order to produce energy transfers. The fourth technique was free; it was one used spontaneously by the subjects. Analyses of variance with repeated measures were conducted and the location of significant differences (p ⩽ 0.1) were made using Scheffé's method of multiple comparisons. The results showed that the work-energy factors and the maximal muscular moments increased with the number of segments participating in the tasks. This was noted predominantly at the level of the lower limbs. Moreover, comparisons between the complete technique and the free technique revealed that the former favoured a more appropriate distribution of efforts at the joints, which thus decreased loading at the lower back and upper limbs. Although the performance using the free technique was slightly higher, it was concluded that the complete technique should be encouraged when maximal pushing tasks are required since loadings (muscular moments) at the shoulders and L5/S1 joints are transferred to the powerful lower limb muscles.