1. 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

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

4. Physical Activity and Obesity
2 constructs
Obesity
Physical activity

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

6. 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.

7. 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

8. 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)

9. 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)

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

11. 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)

12. 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

13. 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]

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

17. Results – Absolute Energy Expenditure
Results - Energy Expenditure (kJ.min-1)
Variable Normal Weight Overweight Obese
Treadmill Walk 11.0 ± ± 2.6 * 16.9 ± 4.1 †
Run 22.7 ± ± ± 8.9
Football Throw 14.7 ± ± ± 6.8 †
Walk 10.7 ± ± 3.8 * 14.1 ± 2.9 †
Bicycle 15.3 ± ± ± 4.4
Scooter 18.3 ± ± ± 5.7
* Sig diff between Normal Weight and Overweight groups, p < .017
† Sig diff between Normal Weight and Obese groups, p < .017

18. Results – Relative VO2 Results - VO2 (ml.FFM-1.min-1)
Variable Normal Weight Overweight Obese
Treadmill Walk ± ± ± 2.9
Run 17.6 ± ± ± 5.7
Football Throw 11.8 ± ± ± 3.0
Walk ± ± ± 2.6
Bicycle 12.8 ± ± ± 3.4
Scooter 14.6 ± ± ± 3.8
No significant differences between means, p > .017

19. Results – Heart Rate Results - Heart Rate (b.min-1)
Variable Normal Weight Overweight Obese
Treadmill Walk ± ± ± 13.8
Run ± ± ± 16.6
Football Throw ± ± ± 13.4
Walk ± ± ± 12.0
Bicycle ± ± ± 15.4
Scooter ± ± ± 16.3
No significant differences between means, p > .017

20. Results – Movement Results - Acceleration (cts.min-1)
Variable Normal Weight Overweight Obese
Treadmill Walk 2628 ± ± ± 463
Run 3063 ± ± ± 242
Walk 9640 ± ± ± 3369
No significant differences between means, p > .017

21. 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)

22. 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

23. 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

24. 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%) …

25. 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

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

27. 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:
Activity Promotion Lab
Promoting Active Lifestyles