Validity of self-reported exercise-induced sweating as a measure of physical activity among patients with coronary artery disease

Background. In several epidemiological studies, self-reported exercise-induced sweating has been used as a measure of physical activity (PA). Among healthy subjects it is moderately well associated with other measures of PA and physical fitness, but its validity among patients with coronary artery disease (CAD) has not yet been established. Methods: In a self-administered questionnaire, 233 patients undergoing coronary angiography replied to the question "In the past 4 weeks, how often have you exercised vigorously enough to work up a sweat?" Patients also gave the frequency and duration of different PA. We examined the association of the sweat frequency question with light (<4 metabolic equivalents [METs]), moderate (4.0-5.9 METs) and intense (>6 METs) PA, and tested the association with maximum exercise capacity. Results: The frequency of self-reported exercise-induced sweating was significantly (p < 0.001) associated with both moderate and intense PA. The correlation coefficient of moderate and intense PA with sweat frequency was r = 0.34 (p < 0.001), and r = 0.44 (p < 0.001) for the respective PA of >30 minutes' duration. The strength of the association between sweat frequency and caloric expenditure per time was similar (moderate and intense PA, r = 0.43, p < 0.001). There was a significant correlation between maximum exercise capacity measured in METs and sweat frequency (r = 0.37, p < 0.001). Conclusions: These results suggest that for studies among patients with CAD, assessment of the frequency of self-reported exercise-induced sweating provides useful information regarding moderate and intense PA as well as physical exercise capacity.