Exercise can release stored THC from fat, potentially causing a positive drug test.

“certain things like exercise for example anything that's going to trigger adrenaline because adrenaline is lipolytic so adrenaline causes fat to metabolize and release stuff that's inside it so there are plenty of cases I've heard from people where they were testing themselves and were negative and then went for a run or went to the gym and then tested positive or lost weight yeah or they've lost weight and anything that's going to cause the the lipolysis to occur so that it releases that THC”