The science of ergonomics focuses on the interactions between work demands and worker capabilities. The goal is to achieve those interactions between the work and the worker that will not only preserve the safety and health of the workforce but also optimize productivity. Applying the science of ergonomics to pushing and pulling tasks produces a number of guidelines for the design of work involving those tasks.
In the first place, it helps to design work to control the amount of pushing or pulling an employee is expected to do. A good example is to set a limit on the number of shopping carts an employee is expected to collect from the parking lot in one trip. When possible, you can limit the need for pushing or pulling by using applicable mechanical aids. Depending on the environment these might include:
- Conveyer belts
- Powered trucks
- Lift tables
- Slides or chutes
The force required to push or pull can be lowered by reducing the size and/or weight of a load or using four-wheel trucks or dollies. Proper selection and maintenance of hand-trucks and dollies is very important. Wheels or casters should be adequately maintained and bearings should be periodically lubricated. Be sure that the equipment is sized to the task properly, such as with larger diameter wheels and casters for heavier loads.
Floors also affect the ergonomics of pushing and pulling. Floors that are not level increase the difficulty of pushing or pulling, as do floors that are rough. Maintaining floors and applying a surface treatment that reduces friction might be advisable.
Reducing the distance of the push or pull is an easy way to improve the ergonomics. Two examples would be moving receiving, storage, production, or shipping areas closer to work production areas and changing the production process to eliminate unnecessary materials handling steps.
Finally, the actions of pushing and pulling can be optimized by:
- Providing variable-height handles so that both short and tall employees can maintain an elbow bend of 80 to 100 degrees.
- Replacing a pull with a push whenever possible. Using ramps with a slope of less than 10%.
Keep in mind that a number of factors influence the ergonomics of horizontal pushing and pulling. These include body weight, height of force application, distance of force application from body (amount of trunk flexion/extension), duration of force applied or distance moved, and the availability of a structure against which the feet or back can push to prevent slippage. For vertical pushing and pulling, the influential factors include grip strength and height of force application. The height determines which muscles will be used. Pulls from above head level allow for the greatest force because body weight can be used. Pulls from more than 10 inches above the floor also allow the greatest force because strong leg and trunk muscles can be used. Pushing across the front of the body involves weaker shoulder muscles so full arm extension leads to a marked decrease in maximum force.