A lot of the fat is probably removed with the sweat but we know for sure that fat cells are expelled in urine. If you work out wouldn't the fat cells carrying the thc leave your body when you urinate. Can you cause yourself to have a positive test when you otherwise would not have just by working out.
Anytime fat cells burn, the stored THC metabolizes into THCA and is released back into the bloodstream, to where they are filtered by the kidneys and deposited into the bladder.

A sizeable portion of THC metabolites are excreted via the bowels, but B/M is not the preferred specimen type for drug analysis.
Very little THCA is excreted via sweat. You can sweat buckets, yet the amount of THCA being excreted will still be miniscule. The rest are being excreted via urine and bowels.

If a person still tests positive on a home kit (with the first days' void), then all fat-burning activities should be avoided and be as dormant as possible for 3 days prior to the U/A to avoid releasing a bunch of THCA into the bloodstream, which will end up in the urine to be detected.