If your standard running routine needs an adrenaline boost, maybe flesh-eating zombies will do the trick.
An app called Zombies, Run!, is a narrated game where real-world runners must out run zombies and collect supplies to keep themselves and their fellow humans alive - and the only way to do that, is to hit the pavement.
"When you're out running, you'll occasionally get chased by zombies and you'll need to speed up in response over the next minute," said the app's co-creator Adrian Hon.
"That's very much like interval training, which is one of the best ways to get fit and to improve cardio. But it's incredibly hard to make yourself do it because it's painful. But when you're being chased by zombies, well that's another thing," he said.
The story, performed by professional actors, plays out in one to two minute acts interspersed between the music runners already have on their devices. As players progress throughout the game, they start uncovering the mystery of how this futuristic world came to be filled with zombies.
Each mission that players embark on is approximately half an hour and there are currently 13 missions available, with 17 more in development. Players advance in the game by automatically collecting supplies like medicine, batteries and water for fellow humans back at their base.
"You hear the sound of the gates of the base you live in going up and someone says, 'The gates are broken -- we've got an emergency' and suddenly the megaphone goes on and tells you to report to the gate immediately 'Go, go, go!'", said Hon about the beginning of mission three.
"Every time I hear it, I still speed up. And it puts a smile on my face because I think 'OK, let's go for it'" he said.
Created in conjunction with award-winning novelist Naomi Alderman, the motivation for the app was to use the power of storytelling to make running more entertaining and motivating.
"For a lot of people who want to get into running it's been a great motivational tool. But we also have people who are running for an hour or two hours just because they want something more interesting than music or a podcast," she said.
Hon, who started running a few years ago, said that while apps that provide badges or points for running are motivating, they lack the engagement factor that he believes many runners need.
"They don't make the act of running anymore fun. You might be running and thinking 'I can't wait to get home to add five more points to my running log' but it's not really any greater when you're out there," he said.
An upcoming update to the app will track metrics such as speed, distance, time and calories burned. The company is also working on two add-on packs: one for beginners to ease them into running, and the other for interval training, for which Alderman said the app is particularly useful.
"We have all the built-in instincts in our brains to run away from predators. So it's a really powerful motivation to use," she said.
The app is available for iPhone and Android devices.