Man City's Richards: Pellegrini training more intense than Mancini
The 25-year-old returned to action as he was named captain for the Capital One Cup third-round tie against Wigan at the Etihad Stadium.
Richards told the club's matchday programme: "I think pre-season took its toll because we had a lot of games and there was a lot of travelling, and whereas some of the guys are fine, being a bigger lad, it takes my body maybe a couple of days longer to recover.
"Under Roberto Mancini, the intensity in training was a little lower - that's not a criticism of Manuel Pellegrini's methods - it's just that the workload has increased and it's going to take the players time to get used to it.
"We'll get used to it and ultimately it's to our benefit because we'll get fitter and stronger as time goes on."