The Mack Nevada feat. Mark Morrison & Fetty Wap Download 'The Mack' on iTunes
The 'Next To You' singer is working on buffing up.
Justin Bieber is using his mini-break from music to get bulky by switching up his diet and exercise routine.
"Justin's naturally quite wiry but he's trying to develop a more muscled physique," a source spilled to the Daily Mirror.
"As well as hitting the gym he has been assigned a nutritionist who has upped his protein intake and is making him eat every three to four hours."
Justin's track 'Next To You' with Chris Brown was new in the Vodafone Big Top 40 on Sunday.