Load on knee joint and knee muscular activity during machine milking

Abstract

Ten professional milkers simulated 20 different standardized machine-milking work postures. Various differences in level between milkers and cow, and various postures at each level, were studied. Knee muscular activity was recorded electromyographically. In the milking procedure when attaching the teat cups to the udder the body position was photographed and the loading moment of force about the bilateral knee axis was calculated by means of a biomechanical model. Working with straight knees resulted in comparatively high moments tending to extend the knee (with the highest mean of 56 N m). This moment was for some subjects close to their maximum strength capacity. A 65° knee angle in the standing postures with small level-difference between cow and milker gave the least knee loading moment (i.e. around zero) independently of body weight. The horizontal distance between operator and cow showed high importance for the amplitude of the knee load. The model for determining knee load can generally be applied to other similar activities when standing bent forwards.