Anyone who has stepped on a treadmill for the first time in months knows how quickly breath leaves unfit lungs. Fitness and how hard one can push themselves has so much to do with how easy it is to breathe. PrO2 is a device that can monitor a baseline breath and with that create a training program to help build endurance and ease of breath. Sending its readouts to any smartphone or tablet, PrO2 is quick and easy to use. The wait-and-see approach of PrO2 feels outdated, however, considering the real-time input/output cycle of wearable fitness trackers and even breathing trackers like Spire. PrO2 will hit the ground running in September for $199.