Hand-arm transmitted vibration originating from a 15 horsepower single-axle tractor can be very strong and cause operator fatigue plus various physiological disorders in vascular, neurological, and musculoskeletal systems. The objective of this work was to measure the characteristics of such hand-transmitted vibrations and its effect on the health of the single-axle tractor operator, in a research program conducted at the Melkasa Agricultural Research Center of Ethiopia. During the study, the measurement of anthropometric data and the heart rate of the operators and vibration at the handle of single axle tractor were conducted. From measured data, the requirement of expenditure energy, physical workload, and operators’ daily vibration exposure was calculated. The average measured resting heart rate, working heart rate and heart rate after the operation was 717, 1624 and 12624 beats/min, respectively. The calculated values of HR reserve (%HRR) or physiological workload and the ratio of working to resting heart rate were 7410% and 2.30.4 (p < 0.0001), respectively. The total energy expenditure of single-axle tractor operators was calculated to be 351.2 kJ/min. The daily exposure m/s2A (8) and total exposure points which were calculated indirectly from measured vibrations at the tractor handle and duration of operation were 12.6 m/s2 and 2520 points, respectively. From measurements of operators’ heart rates, it was concluded that the physical workload fell into the category of extremely heavy work, for which the working heart rate more than doubled the resting heart rate (p < 0.0001).
Key words: Tractor vibration, hand-transmitted vibration, single-axle tractor, heart rate, physical workload, vibration exposure.
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