Purpose: To effectively evaluate activity-based interventions for weight management and
disease risk reduction, objective and accurate measures of exercise dose are needed. This study
examined cumulative exercise exposure defined by heart rate-based intensity, duration, and
frequency as a measure of compliance with a prescribed exercise program and a predictor of
health outcomes.
Methods: 1,150 adults (21.3 ± 2.7 yrs) completed a 15-week exercise protocol consisting of 30
min/day, three days/wk at 65-85% maximum heart rate reserve (HRR). Computerized HR
monitor data were recorded at every exercise session (33,473 valid sessions). To quantify total
exercise dose, duration for each session was adjusted for average exercise intensity (%HRR) to
create a measure of intensity-minutes for each workout, which were summed over all exercise
sessions to formulate a heart rate physical activity score (HRPAS). Regression analysis was
used to examine the relationship between HRPAS and physiological responses to exercise
training. Compliance with the exercise protocol based on achievement of the minimum
prescribed HRPAS was compared to adherence defined by attendance.
Results: Using HRPAS, 868 participants were empirically defined as compliant, and 282 were
non-compliant. HRPAS-based and attendance-based classifications of compliance and adherence
differed for approximately 9% of participants. Higher HRPAS was associated with significant
positive changes in body mass (p<0.001), BMI (p<0.001), waist and hip circumferences
(p<0.001), percent body fat (%Fat, p<0.001), systolic blood pressure (p<0.011), resting heart rate
(RHR, p<0.003), fasting glucose (p<0.001), and total cholesterol (p<.02). Attendance-based
adherence was associated with body mass, hip circumference, %Fat, RHR, and cholesterol
(p<0.05).
Conclusions: The HRPAS is a quantifiable measure of exercise dose associated with
improvement in health indicators beyond that observed when adherence is defined as session
attendance.