This paper presents results of a study conducted to estimate lower back loadings in cart pushing and pulling. Experiments were conducted in the laboratory using a cart. Six subjects with different weights (ranging from 50 to 80 kg) were tested for three different pushing and pulling forces (98, 196 and 294 newtons), three different heights of exertion (660, 1090 and 1520 mm high) and two different moving speeds (1.8 and 3.6 km/h). It was found that, in general, pushing a cart results in lesser lower-back loading than pulling. Subject body weight affected the lower-back loadings more significantly in pulling (50% increase as body weight increased from 50 kg to 80 kg) than in pushing (25% increase). Handle height of 1090 mm was found to be better than other handle heights in pushing while 1520 mm handle height was better for pulling in reducing lower-back loadings.

Priority dispatching rules and shop load affect jobshop performance. This paper evaluates ten different priority dispatching rules with respect to six different performance criteria under light, medium and heavy shop loads. Simulation was used as a tool to determine the rankings of the dispatching rules for a given shop load and performance criteria. A comparative study was conducted to investigate the performance of these rules. Two rules, 'shortest processing time' and 'least work remaining'. performed well under criteria related to the processing time. It was found that the rules that perform well in average and r.m.s. tardiness perform poorly under percentage-of-jobs-late criterion. The experimental results are conveyed with critical comments on the performance of the dispatching rules under different loading conditions of the shop.

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The objective of this study was to evaluate five different lifting tasks based on subjective and biomechanical estimates of stress at the lower back. Subjective estimates were obtained immediately after the subjects performed the lifting tasks. Rankings for different tasks were obtained according to the perceived level of stress at the lower back. A biomechanical model was used to predict the compressive force at the L5/S1 disc for the weight lifted considering link angles for the particular posture. The tasks were also ranked according to the compressive force loading at the L5/S1 disc. The weight lifted in these tasks for obtaining the subjective estimate of stress was the maximum acceptable weight of lift (MAWOL). This was determined separately for each subject using a psychophysical approach. Subjective estimates of stress were obtained for infrequent lifting, specifically for a single lift, as well as for lifting at a frequency of four lifts per min. The results showed that a lifting task acceptable from the biomechanical point of view may not be judged as a safe or acceptable task by the worker based on his subjective perception. This may result in a risk of the worker not performing the recommended task or not following the recommended method.

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