Prison Break: The Conspiracy

The heavy bags, otherwise known as punching bags are located in all the prison yards, you can get this achievement as early as the first chapter, after your confrontation with T-Bag.

Once you're on one all you need to do is follow your trainers command, he'll call out what action and then you follow up by throwing the correct punch, you can either farm this in one session or just do bits here and there.

I got this achievement in Episode 7, which is the 2nd time in game you'll be able to go and hit the sandbag.
I was wondering how long it would take, when it popped just as I maxed out my strength on the bag.
Hitting the bag you'll be instructed to press buttons. You'll here the guy saying 3 different phrases, which correspond with A, X or RB.
Not hard at all.

/edit: block is RB.. thanks :)