Photo: glennji, Flickr

How trustworthy is your heart monitor? Whether you're glancing at a wrist piece all day long or shimmying into the chest belt during workout-time only, you should know what the latest research is saying about accuracy. Especially that number the fitness masses pay so much attention to -- calories burned.

A new study published in the Journal of Strength & Conditioning Research compared calorie-burn results from a Suunto heart monitor with a proven calorie-burn laboratory test measuring oxygen consumed and carbon dioxide expelled. Yeah, it's obvious why these wrist-gadgets are so popular, measuring the length between heart beats is way more convenient than tossing a mask in your gym bag.

The Suunto was most reliable during low-intensity, everyday activities such as typing at your desk or washing the dishes. Encouraging news for everyone micro-managing their all-day calorie burn. However, the Suunto was considerably less accurate when the sweat started dripping, underestimating calories burned by about 13 percent during a real workout.

As heartbeat monitor junkies chew on these results, the real question is, "What does this mean for me?" If you just finished an intense half-hour on the treadmill and the Suunto says 350 calories burned, perhaps you really burned 395. Not exactly a green light for dessert. Listen to the true chief -- your scale. And when it comes to grabbing those sensors, calorie-burn estimates vary by cardio machine, too.