Workload evaluation under unstable floor conditions

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The purpose of this study was to objectively evaluate the workload on an unstable standing condition. The following results were obtained.1)When subjects walk on a slippery floor, the subjects changed their postures to reduce the required coefficient of friction. However, the muscles of the lower limbs co-contract and muscle activity rises overall. A subjective evaluation of the load on the lower limbs revealed that subjects feel the load at upper leg was lower than those at lower leg. Moreover, the antiskid safety shoes were effective to reduce the muscle activity.2)At the luggage carrying task on a slippery floor, muscle activity tended to rise as the luggage became heavier and bigger. Foot pressure measurement has shown that the ratio of the force applied to the tiptoe increases when the floor is slippery. The subjective complaints concerning the upper body were affected mainly by the size and weight of the luggage, whereas those of the legs were affected mainly by the floor conditions.3)To examine the influence of an inclined floor, a quiet standing task and foot-stepping task were conducted on a floor that inclined from front to back and from side to side. Electromyogram activity rose during both tasks when the gradient increased. Moreover, electromyogram activity was higher when subjects were on a laterally inclined floor than when they were on an upwardly or downwardly inclined floor. When the gradient increases, the energy consumed increases. The subjective complaint on the upwardly inclined floor was high, and that by subjects in quiet standing on the laterally inclined floor was lower than the other floor condition.4)An expression to evaluate workload at an unstable condition according to both muscle activity and energy consumption was made based on these two sets of experimental data.