Polar's intriguing new sleep tracking system, called Nightly Recharge, calculates a Sleep Score for overall sleep quality, but also measures ANS (Autonomic Nervous System) recovery by calculating heart rate variability, heart rate and breathing. Both measurements combined determine how Polar's fitness app calculates the intensity level your next day's workouts should be at.
Then, a coaching system called FitSpark claims to advise on training regimens based on what your Nightly Recharge results are. According to Tom Fowler, president of Polar USA, it could be possible that you'd get a good Sleep Score but not score well on ANS recovery, and as a result, your body may not feel as well recovered.
Compared to Polar's larger ultra-long-life GPS watches, the, the Ignite is a lot slimmer, and has normal-feeling watch straps. It's also meant to be worn all the time, especially while sleeping.
The Ignite battery life should last about 17 hours with GPS and heart rate tracking on, or five days of tracking without GPS. I haven't worn the Ignite yet to test its claims out.