Heart rate and sports monitors appear just about everywhere--in standalone devices, in watches, in bras, in shoes, in GPS devices--so why not just build them right into shirts. Many heart rate monitors need to be strapped to the chest anyway, so a heart-rate shirt seems like a logical conclusion.
Under Armour is using that logic in its new E39 shirt. An unassuming, sleeveless compression base layer by day, the shirt moonlights as a hard-working performance monitor. Actually the monitor is a separate device, known colloquially as "the bug".
Originally designed for tactical use by Zephyr Technologies, the sensor sits inside the sternum area of the shirt and measure all kinds of indicators including heart rate, breathing rate, temperature and three-directional movements.
When you're done exercising, plug the sensor into your laptop, iPad or mobile phone and you'll get a read-out of your workout. Compare it with your last workout; compete with friends and push yourself to do better next time.
The shirt is being tested at the NFL Combine and should be available to us weekend warriors by next year.
Here's a more in-depth explanation:
EDITOR'S UPDATE: The heart rate monitor shirt is currently unavailable. This chest heart rate monitor is a well-rated option as are many heart rate monitor watches.