Max Verstappen has described claims of today's Formula 1 cars being too easy to drive as "bulls**t".

In recent weeks, Lewis Hamilton and Romain Grosjean have both called for a greater physical challenge, suggesting drivers are unable to race at their maximum due to the need to save fuel and tyres.

The comment that most riled the Dutchman, however, was a suggestion by Grosjean that he was more tired after karting than he was an F1 race.

"That's bulls**t to me," Verstappen said at Paul Ricard. "We are now so much faster than we've been in previous years. I don't understand where this is coming from.

"What Grosjean said, I don't understand at all. With karting, you use very different muscle groups.

"If I would go karting now, after 20 or 30 laps I would also be completely messed up. While when I was 15, I could drive 300 laps in one day and had no problems at all.

"Does that mean that I am not as strong as when I was 15? No, not at all. You just use very different muscles. You ask a lot more from your forearms."

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The Red Bull driver also explained how most kart drivers would be much less prepared physically for the strains of an F1 car.

"Look, if you would put mates of mine who are still karting in a racing car, they wouldn't feel their necks the next day, while they drive 300,000 laps a year in a kart," he said.

"So I think this is a very strange comparison."

As for Hamilton's remarks, Verstappen also had a response to the Briton's claim that he could drive two or three races in a day due to the lack of effort required

"If you have such a good car, you can drive at 90 per cent," Max concluded.