Stoffel Vandoorne has confirmed claims that Formula 1 drivers have been preparing hard for 2017.

New drivers like the Belgian, and younger drivers including Esteban Ocon and Carlos Sainz, have been working harder than ever for this year's much faster cars.

It has emerged that Sainz has put on four kilograms of muscle, and Ocon a full five.

"It's already clear that it will be a lot faster," McLaren rookie Vandoorne told Belgian news agency Sporza.

"I have been doing a lot of sports to keep fit. That's the only way, because there's no driving," the 24-year-old said of the winter period.

"The changes in the rules means it will probably be difficult for the drivers. But I don't see it as a problem. I have had a good preparation. The season can start now for me."

Hopes are high for a much better season for McLaren-Honda in 2017, but opinions are actually mixed about how the 2017 car and engine will fare.

Vandoorne said: "I don't know much about it. I have only tested in the simulator, but it is already clear that it will be a lot faster than in previous years.

"The past few years were difficult for McLaren, but the team has also made a lot of progress.

"Hopefully we can start in two weeks with good testing in Barcelona."

McLaren finished sixth in the 2016 constructors' championship.