Assessments by HR and %HRR of occupational work exertion for alternating periods of rest and manual labor.

Objectives: Metabolic equivalents (METs) and relative metabolic rate (RMR) as calculated by oxygen uptake (VO(2)) are often used to assess physical exertion. In practice, accurate measurements of VO(2) are difficult; heart rate (HR) values represent an alternate index of physical exertion. We investigated whether one can assess physical exertion based on HR in the workplace, even if the physical task in question involves alternating periods of strenuous anaerobic activity and rest. We also examined the potential usefulness of assessments based on percentage of heart rate reserve (%HRR) and percentage of oxygen uptake reserve (% VO(2)R).

Methods: Six healthy men were asked to perform several physical movements. HR and VO(2) were recorded in real time.

Results: HR and VO(2) are significantly correlated even under conditions of various repeated intermittent movements including anaerobic exertion. Cumulative fatigue results in inadequate recovery in various parameters indicating sufficient rest times, whereas VO(2) values recover immediately. One movement may generate large differences in HR among individuals, but not in VO(2). We found no significant differences between dispersion for %HRR and VO(2)R. However, as with HR, %HRR values indicated insufficient recovery after strenuous exertion.

Conclusions: VO(2) alone does not adequately reflect the exertion entailed by certain physical activities. HR is more useful than VO(2) in evaluating the exertion required by physical labor in individual workers. While we can use %HRR and % VO(2)R to compare physical exertion from individual to individual, %HRR is more valuable, since % VO(2)R can underestimate physical exertion in recovery periods for the same reasons as VO(2).