Article Information ABSTRACT History: Objectives: Recording devices relying solely on heart rate (HR) are not considered accurate enough for measurement of energy expenditure of occupational physical activity (OPA) and leisure time physical activity (LTPA), due to factors which modulate the heart rate-oxygen uptake relationship such as smoking and cardiorespiratory fitness. This study used HR index which corrects for the effect of smoking and cardiorespiratory fitness on HR, to estimate the

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... cise intensity of occupational activity and determine whether smoking and exercise habits influenced work performance. Methods: A total of 176 hospital employees from five occupational categories (sedentary, ambulant-sedentary, light, moderate and heavy) wore an R-R interval recorder during a standard days' work (mean recording time 6.4±0.9 hours). From HR histogram analysis, resting, mean and peak HRs and mean and peak indices were determined, with oxygen uptake, expressed as metabolic equivalents (METs), being estimated from the HR index equation. Results: Mean index, but not mean HR, showed a progressive increase from sedentary to heavy occupational categories, with the estimated mean MET levels for the entire work period ranging from 2.0 to 3.1 METs for males and 1.9 to 2.7 METs for females. Peak index tended to parallel the increase in mean index. Smoking had the effect of increasing resting HR by 7.5 beats•min -1 with regular exercise participation lowering resting HR by 11.0 beats•min -1 , these two lifestyle factors limiting the accuracy of mean HR for determining exercise intensity Conclusions: Smoking and exercise habit significantly impact on resting, mean and peak HR during OPA and may influence work performance. The use of HR index as opposed to HR may improve the analysis of OPA and provide a simple method for estimation of both exercise intensity and energy expenditure.