Roberts, 25, won both the players' and fans' awards after arriving from Ipswich last summer, but confessed to feeling jaded during the run-in.
He told the Huddersfield Examiner: "I faded a little bit and that was a downside. I've never played so many matches in a season and the intensity of both training and games caught up with me because I was feeling jaded towards the end.
"I know the answer is to improve my fitness and that will be the aim in pre-season, which is going to be crucial.
"Having already experienced Lee Clark's training sessions during the season, I know we're in for some hard work, but it will stand us in good stead."