In the workplace, perceived exertion and the fatigue a person experiences can be a greater indicator of musculoskeletal stress than the actual handling of the objective load (Borg, 1998). It is insufficient to just measure the weight of a load because it does not account for the difficulty of the task being performed (i.e., if the worker has to lift in an asymmetric position) or the capacity of the individual.
In the work environment, the RPE scale is most often used to assess job tasks where the nature of the work is mainly physical. If a job task involves a combination of mental concentration and physical effort, then the CR10 scale is most appropriate for use in assessing perceived exertion.
Snook indirectly used a version of the RPE scale in the development of the Snook's Tables (www.ekginc.com/snook.htm). In his experiment, Snook instructed the participants to adjust the weight of the load so that they were able to lift all day, as hard as they could on an incentive basis. Specifically, Snook instructed the participants to lift "without straining or becoming unusually tired, weak, out of breath, or overheated". Snook allowed the participants to adjust their weights because "Only the individual worker can sense the various strains associated with manual handling tasks; only the individual worker can integrate the sensory inputs into one meaningful response". In other words, individuals are the best judges of their own exertions.
A study done by Legg (1985) investigated the effects of individual differences and rate of perceived exertion. The results of Legg's study show that "maximal aerobic capacity demand, body weight, training, sex, age, and genetic make-up are all factors influencing the ability of a worker in any job" (Legg, 1985). In effect, this may account for the apparent differences in RPE among individuals.
