I started up at week three - It may take a couple of weeks to rebuild stamina depending on amount of weight lost. I dropped around 30 pounds in 4 weeks postop and it took me two weeks at gym to get back to a regular 1 hour workout and four weeks to get some of the strength I loss back. I play tennis, used to play racquetball in college, so it took a little while to get through an entire match. But, start back up and build up the stamina. I had to boost caloric intake from 900 to 1,200 to 1,300 to offset the workout and still lost weight.