Roger Federer's coach reveals key reason for Swiss ace's consistency while praising his fitness level

Roger Federer's return to form has surprised not only him but everyone else on the tennis circuit. It has garnered more attention than usual because he made his comeback after spending six months out with a knee injury.

The Swiss ace has made his best start to a season since 2006 and has won three of the four tournaments he has entered, which includes the Australian Open and two Masters Series titles at Indian Wells and Miami. Federer's fitness coach Pierre Paganini, who has worked with him for 17 years, has labelled the world number four a "special case" and believes it is "passion" for the game that allows him to perform at a high level despite being in the later stages of his career.

The 18-time Grand Slam champion has made it clear that remaining fit and prioritising major tournaments is his goal for 2017 rather than playing multiple tournaments like in the past. Paganini revealed that the 35-year-old still surprises him during training and he is forced to reinvent his ways constantly to keep him motivated.

"Passion, it's a very simple word that is used by many people. For him it's a philosophy of daily life, it allows him to live tennis while he breaths the life. He has found this balance since a while. The same person that lives is the same one that plays and practice... he never needs to suit to the several situations he has," Paganini said, as quoted by Tennis World USA.

"There wasn't any single day in 17 years that he came crawling over here. Sometimes he was tired but at the end of the day he worked more than usual. From this point of view, he is an amazing player. He is a special case, he has an enormous potential, a coordination that makes him being a phenomenal athlete.

"It doesn't mean he needs to work less, but instead he has to work on his strengths even more to make a difference. It's already 17 years and we get surprised each other. He forces me to be constantly creative during the practice sessions in order to keep him motivated," he added.