I am 61 and at 16 weeks. I put my gym membership on hold for another 3 months. I walk about 5-6000 steps a day, do my home exercises at PT dismissed me at 12 weeks and since I feel my knee gets sore more as I don't have the machines to work on and the gym I go to does not either. I don't think at 8 weeks you will be doing what you were at the gym. However you didn't say what you do at the gym. I do water exercises and was told I cannot jump or run in place for at least a year even in the water as the do not want me to displace the knee. I am also very active and this has really thrown me but they say by 6 month to a year I'll be good.