Any athlete knows good recovery is just as important as hard training. But how are we really supposed to quantify rest? That's the question being answered by a new batch of tools designed to help you measure and analyze the easy part of your training. One is Restwise.com, a new Web site and coaching tool that crunches 12 metrics—things like resting heart rate, oxygen saturation, sleep, hydration, and muscle soreness—then sends you a recovery score, telling you how hard your body is ready to push itself again. "Everyone is looking for the next way to gain a performance edge, and quantifying fatigue is the answer," says Restwise co-founder Matthew Weatherley-White. There's also Suunto's new M5 heart-rate monitor, which gauges your workout intensity against your fitness level and tells you how many hours to wait before working out again ($209; suunto.com), and Fitbit, a $99 monitor you wear on your wrist to track the quantity and quality of your sleep. "It's taken me years to figure this out," says three-time 24-hour solo-mountain-biking world champ and Restwise client Rebecca Rusch. "You can train like a world champion, but if you don't recover like one, you're not squeezing 100 percent of the benefit out of your workouts."