Cycling is usually thought of as cardiovascular activity and rightly so. But bike riding also works the skeletal muscles. The production of power to drive the pedals involves complex activation of several muscle groups. Of course, the muscles most used in cycling are the legs, but you use muscle groups through the trunk and upper body. Depending on your cycling discipline, the level activation of these groups will vary.
Stage race pro tips, training for long events, muscle activation for proper mechanics and more is all covered in Episode 240 of The Ask a Cycling Coach Podcast.