Lewis Hamilton said on Thursday Formula One should be a much greater physical challenge for the drivers and they should be as tired as long-distance runners at the end of a Grand Prix.
"I could do two or three races in a row and Formula One really shouldn't be like that. It's a man's sport and a lot of youngsters come in. It's quite easy for them to get straight into it," he said in a press conference ahead of this weekend's Canadian GP.
"You should be physically exhausted after a race -- to the point that it should be exhausting like a marathon," he added.
"If I had a choice, I would go back to V12s -- naturally aspirated engines.
"I would have a manual gearbox. I'd make it harder for the drivers, take away all these big run-off areas you have everywhere.
Asked to reflect on themes mentioned during his appearance on David Letterman's Netflix chat show, Hamilton spoke of his father Anthony, who guided his early career until 2010 when he sacked him as his manager.
"This is nothing that's not been spoken of before," said Hamilton, who conceded their relationship had "not always been great" before adding it was "fantastic now."
"My dad is the greatest man I know and definitely someone I aspire to be a lot like so I am pushing him in the gym. Health is everything."
"The older you get the more you understand the world and yourself. It was a big step for me to go to a plant-based diet and it has a very positive affect on me mentally and physically. I wish I had done it a lot earlier."
He said there were still humps along the way, but he had developed the "tools to handle and deal with them" and was now "in the best place I've ever been."
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