Stay up-to-date on the latest and greatest workouts on Zwift! Sign up for our newsletter and we'll keep you posted on new and the most popular workouts. fit, all these file extensions are used to transfer by file a sport activity (or a track, a workout). The FIT SDK contains a tool (FitCSVTool.jar) to deconstruct. Furthermore, each computer program handles file extensions in a different manner. 5min from 50 to 90% FTP 2min 65% FTP 15x 30sec 125% FTP, 30sec 70% FTP 4min 65% FTP 6x 10sec 170% FTP, 10sec 60% FTP 3min 90% FTP 4x 10sec 170% FTP, 10sec 60% FTP 4min 65% FTP 3min 90% FTP 3min 105% FTP 3min 90% FTP 2min 125% FTP 3min 90% FTP 1min 140% FTP 10min from 75 to 50% FTP TCX Convertor is a great tool for manipulating TCX files. File Extension conversion from FIT to TCX is the conversion of computer file extensions from Flexible Image Transport System to Turbo Cad 3 D Model Text File.