The built-in BiomechEngineTM analyzes your running form and provides advice in real time. The dedicated App. “RUNSPECT” records the results and provides support to improve your running performance and help reduce risk of injury. Features soft rubber rotating fin for comfortable and secure fitting. Since the fin doesn't go over the ear, there is no issue when wearing glasses. As S/M/L size fins and earpieces are included, runners enjoy the ideal fitting experience. The included optional “open type earpieces” let you hear ambient noise such as approaching traffic while running. Enjoy music and feel safe when you run.