Physical Performance Assessment

Physically demanding occupations, such as manual materials handling and public safety, require the use of a variety of physical abilities to perform the job tasks. Because of the need for workers to meet the physical requirements of arduous jobs and the potential for injury, employers use physical performance tests to determine an individual's physical capabilities to meet the job requirements. The physical abilities assessed by the tests are based on the essential tasks [Page 624]and functions, working conditions, and ergonomic parameters associated with a job. These abilities are defined in the following text:

• Muscular strength is the ability to exert force to lift, push, pull, or hold objects. The amount of force generated by a muscle contraction is dependent on the size of the muscles (cross-section) involved and muscle fiber type such as a fast twitch.
• Muscular endurance is the ability to exert force continuously over moderate to long time periods. The length of time a muscle can contract is dependent on the size of the muscles involved, the chemical composition of the muscle tissue, and the muscle fiber type such as a slow twitch.
• Aerobic capacity or cardiovascular endurance is the ability of the respiratory and cardiovascular systems to provide oxygen to the body systems for medium- to high-intensity tasks performed over a moderate time period. Aerobic tasks require continuous oxygen consumption.
• Anaerobic power is the ability to complete high-intensity, short-duration (e.g., 5–90 seconds) tasks. Anaerobic tasks are performed using stored energy in the form of adenosine triphosphate (ATP).
• Flexibility involves the range of motion at the joints including knees and shoulders to bend, stoop, rotate, and reach in all directions with the arms and legs. Flexibility at the joints is dependent on the extensibility of the ligaments, tendons, muscle, and skin.
• Equilibrium is the ability to maintain the center of gravity over the base of support such as feet. Equilibrium involves maintaining and recovering to a balanced position when outside forces, including gravity and slipping on ice, occur.

Combinations of different levels of these abilities are needed for all tasks in which muscular contraction, oxygen consumption, and energy expenditure are required. For example, low levels of muscular strength and muscular endurance in the abdominal and back muscles are required to sit in a chair. However, high levels of these two abilities are required to lift and carry thirty 70-pound boxes. Performance of arduous job tasks typically requires all six abilities, but to different extents. Lifting ten 90-pound boxes from a table and carrying them 100 yards to another table requires high levels of muscular strength and muscular endurance in the arms, legs, and torso, but only low levels of flexibility. The level of equilibrium needed is moderate because gravity is pulling downward as the box is carried forward. Similarly, to avoid falling over when picking up a weighted object, the base of support must be adjusted or widened, for example. This task also requires a moderate level of aerobic capacity because of the weight of the boxes, the distance they are carried, and the duration of the task. Therefore, the physical abilities interact at varying levels throughout performance of all arduous job tasks. The specificity of an ability can be determined through direct physiological measurement such as oxygen consumption, ergonomic measurement including force to torque bolts, or questionnaire data.

...