Exercise dose, exercise adherence, and associated health outcomes in the TIGER study

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 HR-based intensity, duration, and frequency as a measure of compliance with a prescribed exercise program and a predictor of health outcomes. METHODS: One thousand one-hundred fifty adults (21.3 ± 2.7 yr) completed a 15-wk exercise protocol consisting of 30 min·d, 3 d·wk, at 65%-85% maximum HR reserve. 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 (%HR reserve) to create a measure of intensity minutes for each workout, which were summed over all exercise sessions to formulate an HR physical activity score (HRPAS). Regression analysis was used to examine the relation between HRPAS and physiological responses to exercise training. Compliance with the exercise protocol based on achievement of the minimum prescribed HRPAS was compared with adherence defined by attendance. RESULTS: On the basis of HRPAS, 868 participants were empirically defined as compliant, and 282 were noncompliant. HRPAS-based and attendance-based classifications of compliance and adherence differed in approximately 9% of participants. Higher HRPAS was associated with significant positive changes in body mass (P < 0.001), body mass index (P < 0.001), waist and hip circumferences (P < 0.001), percent body fat (P < 0.001), systolic blood pressure (P < 0.011), resting HR (P < 0.003), fasting glucose (P < 0.001), and total cholesterol (P < 0.02). Attendance-based adherence was associated with body mass, hip circumference, percent body fat, resting HR, 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.