Will Smith says he has turned in to a "sex machine" since taking on the role of Muhammad Ali.

The former rapper plays the heavyweight boxer in Ali in a forthcoming biopic.

Smith says his new physique has made him feel like the human equivalent of Viagra.

The singer added: "I'm human Viagra. I'm Willagra. I'm a sex machine now. I'm raring to go every second of the day. My wife's loving it."