Increased physical activity improves aerobic fitness, but not functional walking capacity, in severely obese subjects participating in a lifestyle intervention

OBJECTIVE: To determine the relationship between change in physical activity level and change in directly measured maximal aerobic fitness in severely obese subjects participating in a 1-year lifestyle intervention, and to determine whether change in 6-min walk test (6 MWT) could be used as an indicator of change in aerobic fitness.

METHODS: Complete data on aerobic fitness (maximal oxygen consumption (VO2max) and time to exhaustion on the VO2max test), 6 MWT, and physical activity (Actigraph GT1M accelerometer) were obtained for 21 subjects (mean age 42.6 years (standard deviation (SD) 11.0 years); mean body mass index 39.6 (SD 4.5) kg/m(2)). Multiple linear regression (controlling for change in body mass index) was used to analyse the relationships for: (i) changes in physical activity vs aerobic fitness and change in 6 MWT; and (ii) changes in aerobic fitness vs 6 MWT.

RESULTS: Change in physical activity level was related to VO2max and time to exhaustion (partial r > 0.63, p < 0.003). No significant relationships were found between changes in aerobic fitness and 6 MWT (partial r < 0.22, p > 0.351) or between changes in physical activity level and 6 MWT (partial r = 0.15, p = 0.531).

CONCLUSION: Increased physical activity level over 1 year resulted in increased aerobic fitness in severely obese subjects. Although the sample size was small, these results suggest that change in 6 MWT might not be a good indicator of maximal change in aerobic fitness in this population.