GGT is one of the best indicators. When normal, typically all is well; twice or more the reference limit is too high. Not that it's necessarily good to be above the reference limit by less than this, but moderately over is common when using alkylated steroids and not really alarming.
Serum bilirubin also should be no higher than twice the reference limit. Sometimes people are normally (for them) somewhat above the reference limit even without anabolic steroid use, so a moderate elevation isn't cause for alarm.
Neither GGT nor serum bilirubin become elevated from exercise, so exercise will not be an explanation for abnormal results.
ALT is raised little if at all by exercise, but liver problems can be serious (cholestatic liver damage) even at only 2 times the reference limit.
All three of these being normal is excellent evidence of recovery from alkylated steroid use.
AST indeed goes up from exercise, so it can generate false alarms to go by AST.