Maaca, Boxers believe that only boxing helps to be better boxers,

Well boxers when they train they do a myriad of calestenic type workouts, with a trainer focusing on specific exercises that will make them better boxers - same with basketball players soccer players and other athletes.

If you are going to spend time exercising off your bike I would recommend getting a coach or personal trainer who can build a calestenic type workout that will help you become a better cyclist.