Greg trains athletes and he's not a fan of the heart rate monitor of the Apple Watch. Leo says that nothing is going to beat a breast strap that monitors heart rate. But in time, maybe. The Watch is close accuracy wise, but it's not going to replace a Garmin for more serious, higher performance activity. His best bet is patience at this point. It's early days still. Give it time and it'll not only be more accurate, but it will have more features. Polar straps are supported by the Apple watch via Health Kit, however.