Heavier, faster and more physical, the 2017 cars are subjecting drivers like the Toro Rosso youngster to far greater G-forces through corners that can now be taken flat out on fatter tyres.
As a result, Sainz and others have been putting on muscle over the winter to gain upper body strength. Previously they were more preoccupied with losing weight in a sport where the lightest men have enjoyed an advantage.
Sainz, whose father and namesake was a world rally champion, was vocal last year about the dangers of shedding too much but he told Reuters during testing in Barcelona that the situation was now much healthier.
"This year I have had diets but diets to be fit, not diets to be as slim and as skinny as possible...and because of that, I am a much happier person," said the 21-year-old.
"At the end of 2016 my mum could tell me, every time I was coming home: ‘You look like you are not yourself, you look very skinny, you can see your bones here.’ It’s not normal.
"She’s extremely happy and she now sees a smile on my face when I eat her food, while before I was sitting there sad with a piece of chicken and I was completely annoyed about it."
