Max Verstappen says it is "bullshit" to suggest that Formula 1 cars are not challenging enough, as he admits to being baffled by Romain Grosjean's claims that driving a kart is harder.

Lewis Hamilton prompted a renewed focus on the difficulties of competing in F1 when he suggested recently that driving the current generation of cars was too easy.

His remarks prompted Grosjean to reveal that he had been left more tired from driving a few laps in a kart than he ever is from racing in F1. 

But their comments have not impressed Verstappen, who thinks the challenge of F1 is as hard as it has ever been – and suggests Hamilton's view has only been prompted because his Mercedes is so good.

"That's bullshit to me," said Verstappen about suggestions F1 is not challenging enough. "We are now so much faster than we've been in previous years. I don't understand where this is coming from."

Asked about Hamilton's claims that he could easily do three races in a row, Verstappen said: "If you have such a good car, you can drive at 90 percent."

Verstappen said he also was confused about why Grosjean made so much of finding a kart hard to drive.

"What Grosjean said, I don't understand at all," explained the Red Bull driver. "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.

"It makes no sense at all to make that comparison. 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. So I think this is a very strange comparison."