Frank Rooney is the champion of steps in Washington, DC. On average, he walks and runs about 20 miles (32km) a day.

With sophisticated pedometers linked to social media, exercisers can now broadcast their daily performance to others competing in the area.

"They encourage you... and I give them a little boost that says, 'come on, let's get back into this, I want to see you pushing me'," says Rooney.

Will Woolston doesn't know Rooney personally, but keeps track of his accomplishments as a source of motivation.

"When you see people like Frank, it inspires a sense of awe. I've had to tailor my own expectations," says Woolston.

The race between strangers is an emerging trend in smart phone app design - specifically aiming to change daily behaviour.

Produced for the BBC by Janet Weinstein; edited by Bill McKenna