Is better sleep the key to Olympic gold?
Wearable fitness trackers are a growing market in the US. The industry is worth up to $3bn (£1.8bn) by some estimates.
Wristbands and smart phones can monitor physical activity, calorie intake, heart rate - and now sleep.
One in three Americans doesn't get enough of shuteye, and chronic deprivation can lead to long-term health problems.
Recent research also suggests it has an impact on athletic performance, which is why more and more sportsmen and women are turning to sleep and other fitness trackers to give them a competitive edge.
But how accurate are these wearable technologies? Jane O'Brien has been finding out.
Filmed and edited by Allen McGreevy
Living Online is a series of video features published every Tuesday on the BBC News website which look at how technology converges with culture and all aspects of our daily lives.
- From the section Magazine