Murray has already improved his fitness this season

Murray told his official website: "I just want to put about eight or nine more pounds on, then I will be happy with that weight.

"Roger Federer is a good person for me to look at as he has big legs and was thin in his upper body as a youngster."

Murray's next test is in the last eight of the San Jose Open against Hyung-Taik Lee on Saturday at around 0500 GMT.

Murray, the defending champion in San Jose, has already vastly improved his fitness with a good spell of winter training in California.

He had a good year last year and it will be my toughest match so far Andy Murray on Hyung-Taik Lee

The 19-year-old worked with his coach Brad Gilbert and Olympic sprint legend Michael Johnson to build up his stamina and speed.

Murray has now set himself further fitness targets but says it is totally unrealistic for him to get anywhere near the muscular build of world number two Rafael Nadal.

"Me and Nadal have completely different body types so in terms of looking as bulky and thick as him, probably not, but I hope to be as strong," said Murray, who lost to 20-year-old Nadal at the Australian Open last month.

"Just because you have bulk like that doesn't necessarily make you more efficient.

"It also depends how you determine strength. Is it how long you can last, how hard you can hit the ball, how big you can serve, how much weight you can lift, or who has more muscles?"

Murray will be aiming to use all the physical attributes of his game to get past Lee, the world number 54, as he continues the defence of his title in California.

"He had a good year last year and it will be my toughest match so far," said Murray.