Commodus is wearing a brief wrap around his midsection in one shot - in the next shot, he's in a full tunic.
The actor portraying Commodus is clearly in his twenties, but at the time of the events of this episode, Commodus was approximately thirteen years old.
If Commodus was as lazy, pathetic and unconcerned about anything other than whoring and drinking, then he would not be as ripped/toned as the actor who portrays him would be. If that were the case most of the men in the world would look like that.