Michael Schumacher says he has already lost three kilos as he continues to prepare for his return to grand prix action in Spain.
The seven-time champion admitted, however, that he needs more work on his neck, which is still hurting slightly.
"I'm currently in the midst of my preparations for the upcoming race," Schumacher wrote on his website. "I already lost three kilograms even if it is also important to me to build up muscles. So all in all, the practice works pretty well.
"I only have to admit that my neck pinches a bit. We have to get a grip on that as health has priority - that's the clear arrangement made with Ferrari and, by the way, with my wife, too.
"It's on! I accepted the challenge. And as you all know, I really love challenges. It seems as if my fans would love them, too."
Schumacher was also thankful for the support he has received since it was announced he would replace Felipe Massa at the European Grand Prix.
"I really would like to thank all my fans who keep their fingers crossed for my plans for all the positive feedback. It's incredible how much support I get from all over the world in these days.
"It almost feels like as if a flush of positive energy is coming over me. Compliments to all of you!"