Borussia Dortmund and Germany defender Mats Hummels says his poor form last season was down to him being overweight.

Hummels told kicker that, after winning the World Cup in the summer, he overindulged during his summer break, resulting in a struggle for form which lasted right up until the winter break.

"The first half of last season was probably the worst I have ever played in my life," the 26-year-old said. "It felt hefty, and it looked hefty. It was catastrophic for me in terms of my weight.

"I was carrying the weight of eating out of frustration, and since the first half of the season was so frustrating, I got myself caught in a bit of a vicious circle."

Mats Hummels had a disappointing season with Borussia Dortmund. Lennart Preiss/Bongarts/Getty Images

Hummels has been working hard this summer to ensure he goes into the new season with a better physique, and hopefully the right condition to help Dortmund avoid the toils that saw them hit the bottom of the Bundesliga in January.

"I actually do weigh less now," he said. "I'm coming back in a totally different condition to 2014.

"I've eaten well and probably run a bit more during my holidays this summer than I did in all the last years added together."