Mercedes have amended their schedule in Barcelona following the "unprecedented mileage levels" set by Lewis Hamilton and Nico Rosberg.
Hamilton was due to take over testing duties from Rosberg on Wednesday, but the two drivers will now split their schedule.
Rosberg took to the cockpit the W07 this morning with Hamilton, who earlier arrived in the paddock on a hoverboard, to drive this afternoon.
Following the second day of this week's opening winter test, Mercedes had already clocked up five race distances.
Hamilton, the triple-world champion, racked up 156 laps in on Monday before team-mate Nico Rosberg added a further 172 to their impressive tally.
"Nico will drive the #F1 W07 Hybrid beast this morning with Lewis at the wheel this afternoon," Mercedes said.
"Tomorrow will see the drivers split duties once again: Lewis in the morning, Nico in the afternoon... #F1 #WeAreW07
"Why? With the unprecedented mileage levels seen thus far in Barcelona, we want to keep our boys in top shape for Melbourne!"
While Ferrari's Sebastian Vettel has headed the order here on both days, it is the impressive number of laps completed by Mercedes which has caught the eye.
Indeed Fernando Alonso warned that the Silver Arrows, who have dominated the sport for the past two seasons, are looking "stronger than ever".
He said: 'I think the Mercedes domination has not finished, They are very, very strong and they have had some interesting days.
"With that amount of laps it means they have very clear things so when they put that together with their potential they are stronger than ever probably."
Meanwhile the Formula One Strategy Group, which met in Geneva on Tuesday, have agreed to an overhaul on the structure of qualifying, with details expected to be confirmed by the FIA later today. Reverse grids, which had had been on the agenda, will not be among the changes.