Cuellar believes that the Black Cats, who narrowly escaped relegation from the Premier League last season, will be in better shape come the business end of the 2013-14 campaign.
"The way we'll approach this pre-season, I think it will make us a lot stronger physically," Cuellar told the Shields Gazette.
"In the last few games of last season, you could see the players pick up little injuries or cramp because we were working so hard to win every match.
"Sometimes you give more than 100% and we didn't have that extra fitness we needed. I don't think we're going to have that problem next year."