Mercedes' "unprecedented mileage levels" has forced the team into changing its driver line-up for the final two days of the first Formula 1 test.
With reigning champion Lewis Hamilton completing 156 laps on the opening day on Monday, and Nico Rosberg following up with 172, Mercedes has opted to split their running into half-days for Wednesday and Thursday.
Hamilton was scheduled to spend a full day in the car Wednesday, with Rosberg following up with an all-day run on Thursday.
However, the split means Rosberg is behind the wheel on Wednesday morning, with Hamilton taking over for the afternoon, with the reverse for Thursday with the Briton up first.
Via its Twitter feed, Mercedes said: "Nico will drive the W07 Hybrid beast this morning with Lewis at the wheel this afternoon.
"Tomorrow will see the drivers split duties once again: Lewis in the morning, Nico in the afternoon
"Why? With the unprecedented mileage levels seen thus far in Barcelona, we want to keep our boys in top shape for Melbourne."
Speaking at an event in Barcelona on Tuesday, Hamilton explained he had been feeling the strains of completing what was effectively two and a half race distances from his stint at the wheel of the new Mercedes the day before.
"I feel pretty good today, but I'm sore," said Hamilton.
"When you drive the Formula 1 car for the first time, it doesn't matter how much you train, it's like doing a workout.
"If you haven't been to the gym for a couple of months, the next day you have that soreness. It's exactly the same.
"The back of my neck, because of the G-forces we are pulling is crazy, so my neck, I'm feeling it, and my lower back.
"Tomorrow [Wednesday] I guess we're going to be doing even more laps - I think the target is 180.
"What's crazy now is we have a lot less test days. When I first joined Formula 1 at the end of 2006 and beginning of 2007, we had 20 days, or 15 days of driving.
"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.
"So 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 with the advance in technology now the car keeps running. It feels amazing."