Supreme Precision for Endurance Athletes. For endurance athletes who want precise coaching to perfect their training. ZoneOptimizer coaches you to train at the right intensity. Sport profiles guarantee swift switch between different sports. Improves performance with endurance training programs downloadable from polarpersonaltrainer. com with the Polar DataLink. Gives heart rate even in water with a comfortable hybrid transmitter. Race Pace helps you cross the finish line in time. Light (46g) and always ready for use with no need for charging.