Mercedes' unprecedented reliability levels at the pre-season Formula 1 test have prompted it to change in driver plans at Barcelona because of fitness concerns.
The Brackley-based outfit has hit the ground running at the first test, with Lewis Hamilton completing 156 laps on the first day and Nico Rosberg adding another 172 laps on Tuesday.
Although the running has delighted the team – which has openly targeting getting 180 laps under its belt today – it has taken its toll on the drivers.
Speaking at an event in Barcelona on Tuesday night, Hamilton revealed that he was still feeling the effects of running so much on his first day back in the car.
"I feel pretty good today, but I am sore," he said. "If you drive the Formula 1 car for the first time, it doesn't matter how much you train, the next day…
"It's like doing a workout if you haven't been to the gym for a couple of months or something like that. Then the next day you have that soreness. It's exactly the same.
"So the back of my neck, because of the G-forces we are pulling is crazy. So I feel my neck a little bit and my lower back."
Mercedes announced on Wednesday morning that its original plans for the test – to have Hamilton running today and Rosberg on the final day – had been revised.
Instead, the pair will split the duties, ensuring that the single-day demands on drivers are kept to a minimum so their fitness is not compromised for the start of the season.
The team confirmed the reason for the change when it tweeted: "With the unprecedented mileage levels seen thus far in Barcelona, we want to keep our boys in top shape for Melbourne."
Hamilton said that the change of rules for this year – cutting back running to just two pre-season tests – had put extra demands on drivers.
"What crazy is that, now, we don't have a lot of test days," he said. "When I first joined Formula 1 at the end of 2006 and beginning of 2007 I think I had something like 15 or 20 days of driving.
"Whereas now we have less and less of driving for the winter tests. Last year we had 12 days and this year we have eight, which means I get four days before the first race, which is not a lot of days.
"In that space of time we have to do more mileage then ever before to prove out the car.
"Normally the first day the car breaks down lots and lots of times. But now the car just keeps running, it just wouldn't stop. It feels amazing."