Relationship between percentage of VO2max and type of physical activity in obese and non-obese adolescents

The objective of the present study was to determine oxygen uptake (VO(2)) and percentage of maximum oxygen uptake (%VO2max) in obese and non-obese adolescents during various activities in standardised conditions, and the corresponding %VO2max in free-living conditions.

Twenty-seven obese and 50 non-obese adolescents aged 12 to 16 years participated in this study. Body composition was assessed by bioelectrical impedance analysis and dual energy X-ray absorptiometry (DXA), VO2max by treadmill tests, VO2 corresponding to various activities by whole body calorimetry, and time and % VO2max corresponding to various activities in free-living conditions using the heart-rate recording method and a physical activity diary.

VO2max (l/min) was 27.4% higher in obese than in non-obese subjects (p<0.001), but not significantly different after adjustment for fat-free mass (FFM). In the whole body calorimeters, with the same activity program, % VO2max corresponding to sleep and sedentary activities were lower in obese than in non-obese girls (-15.1% and -12.3%, p<0.05), but not significantly different between obese and non-obese boys. However, walking at 4-5-6 km/h corresponded to 47-59% and 71% of VO2max, respectively, in obese, and 34-41% and 48% of VO2max in non-obese subjects (p<0.001). In free-living conditions, moderate physical activities and sports corresponded to 52% vs 35%, and 39% vs 51% of VO2max, respectively, in obese and non-obese adolescents.

In standardised conditions %VO2max did not correspond to the same type of physical activity in obese compared to non-obese adolescents. Consequently, % VO2max is inadequate for comparing the types of physical activities of obese and non-obese adolescents in free-living conditions.