Background Information

The University of Michigan’s Energy Expenditure Prediction Program™ (EEPP) predicts metabolic energy expenditure rates by summing up the energy requirements of small, well defined work tasks that comprise the entire job. The resulting estimate is much more precise than a single table value depicting an entire job, and the required job analysis procedure is accordingly more tedious, but computerization (e.g. EEPP) has made this type of analysis feasible. This method allows energy expenditure analysis of existing jobs as well as simulated, non-existent jobs. This ability to simulate workplaces is important in the job design process. This method also identifies specific work tasks that contribute heavily to an overall high job energy expenditure rate, which facilitates job redesign activities. Following is a brief description of an energy expenditure model using these methodology.

The metabolic prediction model (Garg et al., 1978) is based on the assumption that a job can be divided into tasks or activity elements. The energy expenditure requirements for each task can be added together to determine the energy expenditure of the entire job. The energy expenditures of the tasks are calculated using prediction equations derived from empirical data. The information for each task needed to compute these energy requirements include: force exerted, distance moved, frequency, task posture, lifting technique for lifting tasks, and the time needed to perform the tasks. Gender and body weight, two worker factors, are also needed. The average metabolic energy expenditure rate for the job is then predicted as the average (over time) of the sum of the energy requirements of the individual tasks, plus the energy required to maintain various body postures. The prediction model is described by the following equation:

Ejob = Ebasal + S( Etaskj / Ttaskj )

where:

Ejob = average energy expenditure rate of the job (Kcal/min)

Ebasal = metabolic energy expenditure rate necessary to maintain basal metabolism and posture (Kcal/min)

Etaskj = net metabolic energy expenditure of the jth task in steady state (Kcal)

Ttaskj = time duration of the jth task (min.)

As the equation shows, the energy expenditure prediction model has two basic components.

(1) Energy expenditure necessary to maintain non-work related body energy requirements

(2) Net energy requirements of the various work tasks.

The first component depends upon the energy required for posture maintenance. The energy requirement is a function of gender, body weight, and body posture. Three different body postures can be accommodated by the model: standing, standing bent over and sitting.

The second component is the net metabolic energy expenditures for the various tasks which comprise the entire job. The model accommodates many different work tasks, including both static and dynamic work. The prediction of the energy expenditure of the separate tasks is a function of various factors, as was previously mentioned. Much of the data needed for this methodology can be collected from industrial engineering time and motion studies or from predetermined time systems. Niebel (1982) provides further information.

The accuracy of this prediction procedure depends upon several factors, including:

(1) The completeness and accuracy of the division of the job into tasks (the job analysis must be correct);

(2) The availability of a prediction equation which precisely describes the task that has been identified;

(3) The accuracy of the task equation itself.

For ease of application, these equations have been incorporated into EEPP.

Center for Ergonomics, University of Michigan
1205 Beal Avenue, Ann Arbor
MI 48109-2117, USA
Phone: +1 734 763 2243, Fax: +1 734 764 3451