Defoe has continued his relationship with French fitness guru Tiberius Darau, 70, who started working with the forward in the summer.
The striker said: "The extra work is paying off for me - massively.
"The way I feel now, compared to last season is totally different. I feel really explosive - and that's crucial to the way I play.
"I'm going into games feeling strong. I know that side of it is down to me. The finishing will take care of myself.
"I speak to Tiberius from day-to-day. He keeps me on my toes and he's coming over here next week.
"If I've not played, then he will phone me at home. I'll be sat there at 5pm and he'll ask: "Have you got a pen and paper?" He tells me to write down what I've got to do. It's like homework for footballers.
"It's certainly helped me. It's a long season and I know now I'm going to be strong at the end of it."