Perception Of Moderate Intensity Physical Activity By Onset Of Obesity: A Randomized Crossover Trial

Abstract

Moderate intensity physical activity is typically recommended for inactive adults with overweight or obesity. However, it is unknown whether there is a difference in the perception of moderate intensity by onset of obesity (childhood versus adulthood). PURPOSE: To determine if there was a difference in selection of moderate intensity between inactive adults with juvenile-onset (JO) and adult-onset (AO) overweight or obesity. METHODS:Participants (N=38; JO=18 and AO=20) completed an initial study visit where height, weight, fitness (time to 85% of age predicted HRmax), and weight history (modified Cincinnati Weight History Questionnaire) were assessed. After stratification by age of obesity onset, participants were randomly assigned the order to complete 20-minute moderate intensity exercise sessions on the treadmill and cycle ergometer (separate visits). A standardized script was used to instruct participants to exercise at a moderate intensity. Participants were given an opportunity to change the speed of the treadmill or cycler ergometer power output every 5 minutes of the session. VO2, METs, and HR were measured continually during exercise sessions. Multiple linear regression was used to determine whether exercise intensity (average MET value and % age-predicted HRmax) differed significantly between onset groups while controlling for age and gender. RESULTS: On the treadmill, JO and AO participants selected an average intensity of (mean ± sd) 3.5 ± 0.9 vs. 3.7 ± 0.9 METS which equated to 64.0 ± 7.7 and 64.9 ± 7.5 % of their age-predicted HRmax, respectively. On the cycle ergometer, JO and AO participants selected an average intensity of 3.3 ± 0.9 vs. 3.3 ± 1.0 METS. This represented 65.2 ± 8.8 and 60.7 ± 7.2 % of their age-predicted HRmax, respectively. After adjusting for age and gender, AO participants expended on average 0.13 more METS on the ergometer (0.03 METS on the treadmill) than JO participants (p=0.50, 0.90, respectively). For HRmax, findings were similar (β=0.34, -0.01; p=0.08, 0.95) for the ergometer and treadmill, respectively. CONCLUSION: Perception of moderate intensity did not differ by onset of obesity. However, inactive individuals with obesity selected an intensity at the low end of moderate intensity for both treadmill and cycle exercise resulting in lower overall energy expenditure.