Wooing the opposite sex is an art, and male of the human race cannot claim that it's their territory and only they excel in it. Animal species woo their mates more daringly and colourfully. Australian Kangaroos know how to flex their muscles and pose to attract the opposite sex, and they have impressive biceps to flaunt without hitting the gym.

According to a new study published by the Biological Journal of the Linnean Society, the size of a boomer (male kangaroo) forearms was key to attracting the attention of a flyer (female Kangaroo) and to keep her by his side.

Dr Natalie Warburton and her co-researchers Dr Patricia Anne (Trish) Fleming and Dr Philip Bateman from Murdoch and Curtin Universities had dissected 13 male dead, grey kangaroos and 15 female, with the intention of finding the difference in the muscle mass between boomers and flyers.

"Forelimb measurements showed that whereas female musculature growth was proportional to body size, male musculature was overwhelmingly exaggerated," Dr Warburton said, as quoted in ABC News.

"The larger the males get, the more those individual muscles are worked up, so they are disproportionally larger than the rest of the body," Dr Fleming said to The Conversation.

The research finds that bulkier boomers were able to decimate competition through flaunting their muscles. "If you look at them from front-on, they look like they're body builders and they'll spend quite a bit of time posturing and displaying to females, but also to other males," Dr Fleming said. "Obviously, that's part of their competitive success."

It becomes dangerously difficult for smaller-sized boomers to get a date because the big ones are dominant and are quite controlling when it comes to their females. "There's the possibility of males getting a sneaky mating in but they would have to be very brave," Dr Fleming said.

The big arm muscles may offer male kangaroos "additional advantage from either females finding big forelimbs sexy or alternatively the males which win the right to access the females are then strong enough to overpower any unwilling female," Associate Professor Rod Wells, an Australian marsupial expert from Flinders University, said to The Conversation.