Abstract
High-wire tomato training system requires plants to be periodically lowered. This is hard work because of the heavy plant weight and the awkward handling position. To determine the best handling position for workers, we analyzed muscle loads by using surface electromyograms. Over a season, the average load created by a suspended plant in a greenhouse was 45 N. We analyzed loads in simulated work from integrated surface electromyogram (iEMG) data. Among 10 muscle parts, the trapezius top and front deltoid showed the clearest responses to the load over the vertical distance to the training wire. The relationships between iEMG values and the load at these muscle parts were nearly linear. The iEMG responses were almost the same in one-arm work and two-arm work. For calculations, handling distances were converted in to the worker's height (height ratio). iEMG values were smallest at a height ratio of 0.45-0.55 at the top of the trapezius and of 0.60-0.65 at the front deltoid. Under actual greenhouse conditions, the optimum height of the wire above the work platform was estimated to lie in a height ratio range of 0.60-0.80, which allows good arm movement. The muscle loads of the front deltoid seemed to increase as the horizontal distance to the training wire increases. Too near, however, and the worker collides with the leaves. Therefore, a suitable horizontal distance was considered to be a height ratio of 0.25-0.30.
