You are absolutely corrrect. But I was getting negtives with heavy exercise.

The day of the test, I got a solid negative with a medium (I hope it was medium) dilution. The solid negative line was just one hour before the test.
You were getting negatives because your THCA concentration was diluted to where the sample fell below the cutoff thresholds of the drug assay - not because of the heavy exercise. Without the dilution, you wouldve tested positive for sure because of the exercise.

What also needs to be known is that contrary to popular belief, line intensity has no bearing upon the levels of THCA thats present in a urine sample. As an example, synthetic urine controls (which are totally drug-free) can produce a "faint" line on one assay kit while producing a solid line on another.