Workers use various pushing and pulling techniques in a wide range of activities, such as:

• using manual carts and trucks
• sliding objects such as cartons on flat surfaces (tables, floors, etc.)
• operating tools and controls
• opening and closing doors
• wrapping or enclosing objects in packaging materials

Because these actions are among the most common work activities, they are also the cause of many injuries. However, there are no comprehensive injury statistics. As well, the injuries resulting from these activities are not always recorded very specifically. Most common are overexertion injuries (e.g., back strain). Injuries due to slips and falls are also often associated with pushing and pulling. Additionally, injuries to fingers and hands can result when caught in, on, or between objects (e.g., between a cart and the wall) and to lower legs when bumped by carts. Therefore, existing statistics do not reflect the importance of pushing and pulling as work factors causing injury because the injuries fall into different categories making them difficult to analyze.

Because of the complex nature of body motion during pushing and pulling, no numerical standard has yet been developed that can be directly applied in industry.

Many factors affect the amount of force that a worker can develop in a horizontal push and pull:

• body weight and strength
• height of force application
• direction of force application
• distance of force application from the body
• posture (bending forward or leaning backward)
• friction coefficient (amount of friction or grip between floors and shoes)
• duration and distance of push or pull

Tables 1 and 2 contain the upper force limits for a variety of pushing and pulling tasks. They indicate the amount of force that a worker should exert. It is important to be aware that the forces in the tables are not the same as the weight of objects being pushed and pulled. This difference means that we cannot use these upper force limits as recommendations for weight limits that can be pushed or pulled in the workplace. Only trained personnel using special equipment can measure the forces exerted by a worker.

The values in Table 1 show the upper limits of forces for horizontal pushing and pulling. These limits should not be exceeded in work situations. In fact, it is better and safer if pushing and pulling tasks require lower forces, particularly, where the task requires:

• pushing or pulling an object when the hands must be above the shoulder or below the waist level
• exerting a force for longer than 5 seconds
• exerting a force at an angle not directly in front of the body, e.g.,. not "straight on"

Where a worker can support his body (or feet) against a firm structure higher forces (up to 675N or about 165 lbf or 75 Kgf) can be developed.

* adopted from: Ergonomic design for people at work. Vol. 2, by Eastman Kodak Company, Van Nostrand Reinhold, 1986

** Units of force are: newton (N), kilogram force (kgf), pound force (lbf); 10N is about the same as 1 Kgf or 2 lbf. The values in each unit system - newtons, kilogram force and pound force, respectively - are provided in the table because all are used in the literature and on instruments, depending on the country of origin.

The values in Table 2 show the upper limits of forces for vertical pushing and pulling. Examples of the use of vertical force are operating controls and hand tools. Such activities tend to be of a repetitive nature and physically more demanding than occasional pushing or pulling. Therefore, these tasks should be designed for considerably lower force requirements than those shown in Table 2.

* adopted from: Ergonomic design for people at work. Vol. 2, by Eastman Kodak Company, Van Nostrand Reinhold, 1986

** Units of force are: newton (N), kilogram force (kgf), pound force (lbf); 10N is about the same as 1 kgf or 2 lbf. The values in each unit system - newtons, kilogram force and pound force, respectively - are provided in the table because all are used in the literature and on instruments, depending on the country of origin.