Jordan Burroughs celebrates after beating Andrew Howe in their 75-kilogram freestyle finals match at the U.S. Olympic Wrestling team trials in Iowa City, Iowa. (AP Photo/Charlie Neibergall)

Wrestling might look like a brand new sport to the casual viewer when it makes its Olympic return Sunday.

The world's oldest sport underwent a series of major changes after being forced to apply for reinstatement to the IOC in 2013.

There are now just 12 men's weight classes, compared to the 14 that wrestling had in the London Games. Those two divisions were shifted over to the women's side in a nod to the IOC's desire for added gender equity.

The red and yellow mats have been switched out for navy blue and orange ones designed to make the action more visually pleasing to viewers.

So too have the old red and blue uniforms, replaced with singlets based on a wrestler's national colors.

The rules have also been tweaked to encourage action. Matches now feature two three-minute periods with cumulative scoring, a move designed to stop wrestlers from sitting on a lead as they often did under the old best-of-three format.  

Here are some of the main storylines to follow during the Olympic tournament, which kicks off with the Greco-Roman discipline.

GRECO-ROMAN

Cuban heavyweight Mijian Lopez can join Russian great Alexander Karelin and Sweden's Carl Westergren as the only Greco wrestlers with three Olympic gold medals. ...Iran's Hamid Soryan will be seeking his eighth world-level title. ...Andy Bisek of the U.S. is arguably the best shot his country has at a medal. The Americans went home empty-handed after the London Games.  

WOMEN'S FREESTYLE

Japan's Saori Yoshida and Kaori Icho will each attempt to win their fourth Olympic gold medal, something no other wrestler has ever accomplished. ...Adeline Gray is the heavy favorite to earn the first gold for a female wrestler in U.S. history. ...Battsetseg Soronzonbold is perhaps the best chance Mongolia has ever had at winning the Olympic tournament.

MEN'S FREESTYLE

Jordan Burroughs of the U.S. will shoot for his second straight Olympic gold medal and his fifth world championship overall. ...Russian youngster Abdulrashid Sadulaev, a two-time world champion, is the heavy favorite at 86 kilograms. ...Kyle Snyder became the youngest world champion in U.S. history last year, but he'll face heavy competition at 97 kilograms.