The Effect of Task Frequency on Risk of Biomechanical Overloading of the Upper Limbs in Manual Pruning in Vineyards

Objectives Among the factors affecting the risk of biomechanical overloading of the upper limbs, repetitiveness is certainly the most important. In manual pruning of vineyards repetitiveness is closely linked with the frequency of cuts and technical actions in unit time. The aim of the research was to assess the interaction between independent variables (tool used for pruning, vine species pruned, work times) and the variable dependent (cut frequency). The data collected made it possible to extract the representative frequency for time periods and calculate the Ocra Index for each period, to compare the results obtained with the index calculated on the basis of the average daily frequency and, finally, to trace the progress of the work productivity curve during the day. Methods The action frequency was evaluated with analytical counting of the technical actions by re-examining video films of the work in slow motion. Statistical analyses were carried out with the publicly available software R. Statistical analysis of cut frequency was carried out using data collected from 18 pruning operators. Two tools (traditional shears and long handled hacksaws), three species (Nero d’Avola, Merlot, Nerello mascalese) and three different time periods were considered. Eight repetitions were carried out for each pruning operator. The influence of the above factors was extrapolated by means of variance analysis (ANOVA). Subsequently, given the highly significant results for the first and second order interactions, in two pruning sites (traditional shears and long handled hacksaw) the respective daily work productivity curves of the workers were found, further sub-dividing the work day (7÷15) into thirty minute periods. Results The workers’ work productivity curves depends not only on the characteristics of the site (species and growing method, tool used for pruning, etc) but above all on the tiredness of the operator, which varies during the day, following a sinusoidal curve similar to that found in other work sites (Blandini et al., 1981). Calculating Ocra index per each hour or per short time slots enhanced a potentially dangerous underestimate that could occurs when we used the daily average value. When we carry out studies about agricultural activities, in which frequency can varies consistently throughout the day, that circumstance must be take in account to preserve health and safety of workers.