Boundary line between the strength and endurance regions in manual lifting

Rating of acceptable load in manual sorting of postal parcels

The psychophysical test, the rating of acceptable load (RAL) were used to assess acceptable weights for dynamic lifting in postal workers engaged in sorting parcels. The standard test (RALSt) and a work-simulating test (RALW) were administered to 103 volunteers: all experienced male sorters. In the RALSt, subjects selected the weight which would be acceptable for lifting in a box with handles from table to floor and back to the table once every 5 min for the working day. for the RALW, the box was without handles and the weight was chosen to be acceptable for transfer 4-6 times/min from a table to the parcel container and back to the table. Both tests were made during normal working hours at postal sorting centres. The overall means for RALSt and RALW were 16.4 kg and 9.4 kg respectively (p < 0.001): both being substantially higher than the average parcel weight of 4 kg. The RALSt and RALW tests proved to be repetitive and sensitive for differentiating the effects of load and task variable in actual manual material handling. Thus they appear to be applicable to the evaluation of manual materials handling problems.

Weight Limits for Foldaway Wheelchairs

Designers have neglected the issue of portability in wheelchair design.

Determination of gross weight limit for foldaway powered wheelchairs through isometric and psychophysical strength simulations

This study concerns the maximum weight of a powered wheelchair for transfer to and from the trunk of a car by individuals with limited exercise endurance. The loading and unloading of a folded wheelchair from the trunk of a medium size American car was simulated. Both static and dynamic simulations were carried out. The isometric (static) and psychophysical (dynamic) strengths of eight adult males while simulating the loading/unloading activities were measured. The results indicated that: (1) the maximum weight of a powered foldaway wheelchair that individuals can load in the car and unload from the car is much lower than the weight of most commercially available powered wheelchairs, and (2) static simulation of the folded wheelchair loading and unloading activity provides wheelchair weight ceiling that is easily exceeded during the dynamic simulation of the activity. The upper limit on the weight of a foldaway powered wheelchair is provided and implications of this limit on future foldaway powered wheelchair designs are briefly discussed. In addition, the user gender and age effects on the foldaway powered wheelchair weight ceiling are also discussed.