Hip load moments and muscular activity during lifting.

The load on the hip joint during lifting was studied. Healthy subjects lifted a 12.8 kg box from floor to table level with straight and flexed knees in four different ways. The loading moment of force about the bilateral hip axis was calculated by means of a computerized static sagittal plane model. The highest load moment, 124 Nm, occurred initially in the straight knee lift and the compressive joint reaction force was 2.7 times body-weight. The lowest load moment, 82 Nm, occurred in the flexed knee lift with the burden moved close to the trunk, the compressive force was 3.2 X bw. The load moment was also discussed in relation to the strength capability. The EMG levels of seven different hip muscles were normalized and expressed as a percentage of the recorded level of each muscle group during an isometric maximum voluntary contraction. The initial activity in the hamstrings was higher in the straight knee lift compared to flexed knees. The gluteus maximus was activated to a moderate level.