Actually, when fat cells burn, THC is metabolized into THCA and released back into the bloodstream. From there, the kidneys filter in the THCA from the bloodstream and thats how it ends up in the urine to be detected. This is the primary reason why THC carries a longer detection window than most other drugs.

Exercising is beneficial, however it should be avoided in the 3 days leading up to the U/A. The idea is to keep the THC stored in the fat cells during this time, instead of releasing them. This can be done by being lazy as possible and eating large meals complete with your favorite desserts.