Making valid statements about obesity and physical activity: The importance of defining your constructs David Rowe, Department of Sport, Culture and the Arts, University of Strathclyde Matthew Mahar and Jennifer Aull, Activity Promotion Laboratory, East Carolina University Activity Promotion Lab Promoting Active Lifestyles

Physical Activity and Obesity Obesity is often linked with inactivity, insufficient physical activity

Physical Activity and Obesity 2 constructs Obesity Physical activity

Validation Paradigm for Kinesiology (and other disciplines) Definitional Stage Confirmatory Stage Theory- Testing Stage

Definitional Stage Definitional Stage Confirmatory Stage Theory- Testing Stage Consideration of prior theory and empirical evidence to present a description of the nature of the construct of interest.

Two fallacies (Thorndike, 1904; Kelley, 1927) Related to terminology, “labels”, “titles” e.g., physical activity Jingle fallacy Instruments with similar names measure the same construct Jangle fallacy Instruments with different names measure different constructs Can refer to instruments or constructs

Physical Activity - Definition 2 components: movement total (steps, activity counts) time (spent moving) rate (acceleration) patterns (episodic, continuous) energy expenditure total (absolute kJ or kcal) absolute rate (kJ·min-1) relative rate (to mass; kJ·kg-1·min-1) relative rate (to maximal capacity; %VO2max; %HRmax)

Obese and Nonobese Obese children are less physically active than nonobese children (Lazzer et al, 2003; Page et al, 2005; Trost et al, 2001) Conclusion drawn on the movement component of physical activity (e.g., via accelerometry)

Question How does the physical activity of obese children compare to nonobese children? (focus on metabolic/energy expenditure component)

Methods N = 55 girls aged 8-12 years Classified as obese (n = 11), overweight (n = 16), or normal weight (n = 28) Using IOTF standards (Cole, 2000)

Methods Girls participated in 6 activities: Walking on a treadmill at 2.5 mph Walking in an open area Jogging Playing catch with a soft football Bicycling Riding a scooter Self selected “pace” (except TM walking) 6 minutes per activity Randomly ordered

Methods VO2 was measured with a COSMED portable metabolic system Data from the last 2 minutes of each activity were analyzed VO2 was expressed relative to fat free mass (ml.FFM-1.min-1) EE was expressed as kJ.min-1 HR also measured [and acceleration]

Methods – data analysis Oneway ANOVA (obese, overweight, normal weight Post hoc (LSD with Bonferroni adjustment) Critical alpha of p < .017

Results – Absolute Energy Expenditure Results - Energy Expenditure (kJ.min-1) Variable Normal Weight Overweight Obese Treadmill Walk 11.0 ± 2.0 15.0 ± 2.6 * 16.9 ± 4.1 † Run 22.7 ± 5.8 26.6 ± 6.7 28.7 ± 8.9 Football Throw 14.7 ± 3.6 16.5 ± 3.7 20.3 ± 6.8 † Walk 10.7 ± 3.0 13.5 ± 3.8 * 14.1 ± 2.9 † Bicycle 15.3 ± 7.5 18.7 ± 3.6 19.4 ± 4.4 Scooter 18.3 ± 8.4 20.2 ± 3.6 22.6 ± 5.7 * Sig diff between Normal Weight and Overweight groups, p < .017 † Sig diff between Normal Weight and Obese groups, p < .017

Results – Relative VO2 Results - VO2 (ml.FFM-1.min-1) Variable Normal Weight Overweight Obese Treadmill Walk 8.8 ± 1.6 9.9 ± 2.6 10.0 ± 2.9 Run 17.6 ± 4.6 16.6 ± 4.5 17.2 ± 5.7 Football Throw 11.8 ± 3.3 10.8 ± 2.5 11.9 ± 3.0 Walk 8.6 ± 2.2 8.8 ± 2.9 8.5 ± 2.6 Bicycle 12.8 ± 4.8 12.4 ± 3.2 12.0 ± 3.4 Scooter 14.6 ± 6.1 12.9 ± 3.1 13.4 ± 3.8 No significant differences between means, p > .017

Results – Heart Rate Results - Heart Rate (b.min-1) Variable Normal Weight Overweight Obese Treadmill Walk 124.6 ± 12.8 134.8 ± 11.7 131.4 ± 13.8 Run 180.4 ± 14.4 181.5 ± 19.0 174.3 ± 16.6 Football Throw 148.3 ± 19.6 145.7 ± 19.2 146.4 ± 13.4 Walk 128.3 ± 15.5 129.3 ± 12.7 127.1 ± 12.0 Bicycle 149.4 ± 9.9 154.1 ± 15.4 154.1 ± 15.4 Scooter 170.5 ± 20.8 167.8 ± 11.2 171.5 ± 16.3 No significant differences between means, p > .017

Results – Movement Results - Acceleration (cts.min-1) Variable Normal Weight Overweight Obese Treadmill Walk 2628 ± 2862 2284 ± 884 2351 ± 463 Run 3063 ± 1889 2769 ± 812 2330 ± 242 Walk 9640 ± 6892 8076 ± 4373 6646 ± 3369 No significant differences between means, p > .017

Summary/Conclusions Absolute energy expenditure (kJ.min-1): Obese girls consistently expended more energy than normal weight girls for all activities studied Not all differences were statistically significant, although the differences were clinically meaningful (ES ≥ 0.66)

Summary/Conclusions Relative VO2 (ml .FFM-1 .min-1): Relative oxygen consumption for each activity was not significantly (or meaningfully) different among groups after adjusting for FFM, for any activity Suggests that the relative oxygen costs of physical activity at self-selected intensities was similar among normal weight, overweight, and obese girls

Summary/Conclusions Heart rate (b.min-1): Higher (~ 7 b.min-1) in the obese group and in the overweight group (~ 10 b.min-1) compared to the normal weight group during the treadmill walk at 2.5 mph Not statistically significant, but were clinically meaningful (ES ≥ 0.49) Otherwise, HR was similar across groups

Summary/Conclusions Movement (cts.min-1), preliminary data (small n’s): During walking and running at a self-selected pace, consistent pattern for overweight and obese girls to move less (i.e., more slowly) Not statistically significant, but were clinically meaningful (normal weight moved 11%-45% faster than overweight and obese) … … but they also “moved more” during the standardised 2.5 mph TM walk (12%-15%) …

Relevance Absolute energy expenditure – relevant to weight management Relative energy expenditure (intensity) – relevant to programming (adherence) Relative energy expenditure (intensity) – relevant to programming (effects on outcomes such as health, fitness) Using movement as a standard for describing PA may not be appropriate when comparing obese children to other children, or prescribing PA for children of different fatness levels

Bottom Line Defining what you mean by “physical activity” is important …

Useful references Activity Promotion Lab Promoting Active Lifestyles Aull, J. L., Rowe, D.A., Hickner, R.C., Malinauskas, B.M., & Mahar, M.T. (in press). Energy expenditure of obese, overweight, and normal weight females during lifestyle physical activities. International Journal of Pediatric Obesity. Rowe, D., & Mahar, M. (2006). Construct validity. In T. Wood & W. Zhu (Eds.). Measurement theory and practice in kinesiology (pp. 9-26). Champaign, IL: Human Kinetics. follow up contact/questions: david.rowe@strath.ac.uk Activity Promotion Lab Promoting Active Lifestyles