The club have spent nine days training with Bundesliga side Borussia Moenchengladbach, and brought their time in Germany to an end with a 0-0 draw against their German hosts.
Cattermole believes that the Wearsiders have improved thanks to their preparations in Germany, and are beginning to reach the fitness levels required for the new Premier League season.
He told the club’s official website: “We are happy with the time we’ve been away.
“We’ve only had one day off and have been doing double sessions most days.
“The games have been tough and we went into today’s game on empty really, but it’s all in the bag now and we will go forward fitter and stronger.
“The lads have all played the same sort of minutes each and to get a clean sheet today was encouraging.
“We’ve still got three weeks until the start of the season.
“It’s a different style of football over here which made it harder for us to press.”
Sunderland have also had games against Arminia Bielefeld and Hannover 96, and Cattermole, who was signed from Wigan Athletic for £6 million in 2009, believes the club’s time in Germany will stand them in good stead for the Premier League season.
The Black Cats begin their Premier League campaign away to Liverpool on August 13, and will be looking to build on their impressive 10th place finish last season.
Sunderland manager Steve Bruce has said he is aiming to finish even higher this season, and the club have made 10 signings this summer to try and achieve that.
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Sunderland captain Lee Cattermole impressed with German workout