We all think we’re giving workouts all we’ve got, but a new exertion-measuring device can help determine whether our mental grit matches what our bodies are actually capable of doing in the gym. 

That's right--slacking's about to be a thing of the past. Under Armour’s Armour39 digital performance monitor ($150, available in March) consists of a tiny diagnostic computer that you wear strapped around your chest. The gadget tracks your heart rate, calories burned and workout intensity, and ultimately churns out a “willpower score,” which it sends to your smartphone, tablet, or a watch that can be purchased for an additional $200. Check out this video to see how it works:

The high-tech training tool isn’t all that Under Armour’s up to these days. This week the company launched a new “I WILL” campaign, highlighting its commitment to rolling out innovate products for the next generation of athletes. Starting Saturday during the NBA’s All-Star Weekend on TNT, you’ll see UA’s newest TV commercial (below) featuring 22-year-old boxer Canelo Alvarez; 19-year-old Sloane Stephens, the only teenager ranked in the top 20 in the WTA, 20-year-old Washington Nationals outfielder Bryce Harper; and 22-year-old Kemba Walker, a point guard for the Charlotte Bobcats. 

Want another glimpse into the future of fitness? Check out The Coolest Health and Fitness Gadgets at CES 2013.