If someone has been handling something they shouldn’t have, like illegal narcotics for instance, then specialized airport staff can examine their hands to figure out what exactly it is that they have been touching.
They will swab their hands with a wipe that gets put into a machine to analyze what it has come into contact with and can identify a whole range of illegal substances. If a suspected smuggler’s hands are a giveaway, then airport staff will make sure to check both their luggage and their body for contraband.
Staying fit is certainly a commitment. Besides doing the physical training, there are some other factors to consider, like nutrition