Optimum handle height for an animal-drawn blade harrow

A blade harrow is a tillage implement commonly used by the farmers of Central and Western India. The handle is one of the main components of a blade harrow and its height has an influence on operator's comfort as well as work performance. Therefore, this study was carried out to determine the optimum handle height for an animal-drawn blade harrow. Two experiments were conducted with four male subjects to study postural discomfort and physiological reactions separately at six handle heights. Downward force applied by the operator on handle, and depth and speed of operation were also recorded. The lowest postural discomfort was noticed at handle height equal to 1.0 metacarpale III height. Here, the overall discomfort rating was 2.4 on an eight point psychophysical rating scale (0 = no discomfort, 7 = extreme discomfort) and the body part discomfort score was 16.3 (the maximum being 53.8 at working height equal to 1.6 metacarpale III height). The mean heart rate and oxygen consumption at this handle height were 103.9 beats/min and 0.536l/min, respectively. Considering the data of postural discomfort and also of heart rate and oxygen consumption, the optimum handle height for the animal-drawn blade harrow worked out to be equal to 1.0 metacarpale III height, i.e. 637 to 732 mm (5th and 95th percentile values respectively, of metacarpale III height of Indian agricultural workers).