Well, I'm not Mustang18, nor do I have my IFBB pro card, but yes it is fine to fire in the ole bis folloiwing a bi workout. Did id tuesday and the pain was nill. Did one in the other bi the next day(obviously didn't train bis that day) and had some irritation. Following a workout the bi will be filled with blood and circulation will be good thus making the site ripe for recieving medication IM. Absorption will be increased and irritation diluted. Depends of course on what you're shooting, but regardless, it's fine.