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BACKGROUND: Weight loss due to a negative energy balance is considered to be accompanied by a decrease in physical activity. OBJECTIVE: The aim of this study was to investigate whether a decrease in physical activity is sustained during weight maintenance. DESIGN: Subjects were 20 men and 31 women [mean (+/-SD) age: 42 +/- 8 y; BMI (in kg/m2): 31.4 +/- 2.8]. Weight loss was achieved by an 8-wk very-low-energy diet period, followed by 44 wk of weight maintenance. Physical activity measures were total energy expenditure expressed as a multiple of sleeping metabolic rate (PALSMR) and resting metabolic rate (PALRMR), activity-induced energy expenditure divided by body weight (AEE/kg), and activity counts measured by a triaxial accelerometer. Measurements took place at 0, 8, and 52 wk. RESULTS: Body mass decreased significantly during the diet period (10.5 +/- 3.8%, P < 0.001), and this reduction was sustained after 52 wk (6.0 +/- 5.1%, P < 0.001). PALSMR and PALRMR decreased from 1.81 +/- 0.23 and 1.70 +/- 0.22, respectively, before the diet to 1.69 +/- 0.20 and 1.55 +/- 0.19 after the diet (P < 0.001) and increased again after weight maintenance to 1.85 +/- 0.27 and 1.71 +/- 0.23, respectively, compared with 8-wk measurements (P < 0.001). AEE/kg decreased from 0.043 +/- 0.015 MJ/kg at baseline to 0.037 +/- 0.014 MJ/kg after the diet (P < 0.001) and was higher after 52 wk (0.044 +/- 0.17 MJ/kg) compared with after 8 wk (P < 0.001). Activity counts decreased from 1.64 +/- 0.37 megacounts/d at baseline to 1.54 +/- 0.35 megacounts/d after the diet (P < 0.05) and were higher after 52 wk (1.73 +/- 0.49 megacounts/d) compared with 8 wk (P < 0.01). CONCLUSION: A weight loss-induced reduction in physical activity returns to baseline values when weight loss is maintained. This trial was registered at clinicaltrials.gov as NCT01015508.