The 25-year-old is fighting to get back to 100 percent after a pelvic injury but has admitted that his new regime is taking its toll.
The 25-year-old missed the World Cup due to a pelvic bone inflammation following a season with BVB that saw many of the club's first team stricken down with fitness problems as they finished second in the Bundesliga.
Bender has insisted that he is ready to get back to full fitness, despite the preseason training schedule taking its toll, and he was happy with the way Jurgen Klopp's men defeated Chievo 1-0 in a friendly on Friday.MORE: Biggest summer transfers | Soccer's beautiful fans
"I'm torturing myself throughout training," he told Ruhr Nachrichten. "Now we have begun training intensely. My legs are heavy today, but it's all the better that we have beaten Chievo.
"I am now four weeks into my full recovery and it feels very good to be back, even if it is not easy."
Klopp's men defeated the Italian side 1-0 thanks to a strike from Pierre-Emerick Aubameyang and will face Slask Wroclaw in their next friendly fixture on Wednesday.
Dortmund captain Sebastian Kehl announced at the end of 2013-14 that he will retire at the climax of the 2014-15 campaign and Bender is currently one of the front runners to replace the veteran midfielder in this role, having captained BVB during preseason already.