Whether the Minnesota Vikings defeat the Green Bay Packers on Sunday in one of the biggest games of the NFL season will depend in part on the performance of a bike nerd.

Chad Greenway, the team’s second-leading tackler, spends the off-season watching the Tour of Utah and “trying to wrap my head around the impossible things Team Sky accomplishes,” as he puts it. It isn’t just a hobby. He’s one of the growing number of NFL players using hard-core bicycling to train for football.

Greenway can ride up to 60 miles in a day. But he has no fat to burn, and he doesn’t want to burn muscle. So he prefers to go about 20 to 40, mainly in the off-season. When training for football, Greenway said he wants to mimic the game’s short bursts, a fitness technique known as “interval training,” he said. With that in mind, he finds hills around his Minnesota home and climbs them on his bike as fast as possible.

The result? Improved leg turnover, fresher legs, and nearly everything else. “It’s helped my hip girdle, my jabs, it’s huge for the hamstrings,” said Greenway, a two-time Pro Bowl selection. “And it’s a lot more core than you would think, just maintaining your position on the bike works the core.”

Philadelphia Eagles linebacker Connor Barwin is known for making the three-mile trek to work at the Eagles facility on a bike. He is so devoted to it that he’s appeared in advertisements for Philadelphia’s bike-sharing program. Washington Redskins running back Alfred Morris’s parking space at his team’s facility is occupied by his bike. He, too, bikes to work.