Cycling predominantly works your leg and core muscles, which inevitably become toned as you clock up the bike miles:
Glutes – Most active at the top of the pedal stroke just as you’re about to push down. They also provide hip stability and prevent us moving around in the saddle.
Quads – The quadriceps function at their optimum on the down phase of the pedal stroke. Especially the VMO (vastus medialis oblique), which helps to push the big gear.
Hamstrings – The hamstrings flex the knee and pull the pedal upwards. They can easily become underactive due to their over dominant partner, the quads.
Calves – Help stabilise the pedal stoke.
Core muscles – These allow the lower limb to provide stability and power when we cycle. A strong core not only develops functional abs, but can help us become a more efficient cyclist. Your core muscles are in the belly and the mid and lower back (torso), and include transversus abdominis, obliques, rectus abdominis, erector spinae, longissimus thoracis, latissimus dorsi, and trapezius.
Also remember that a strong upper body is just as important as it allows us to hold a better aerodynamic position. The harmonious link between the lower and upper body enables us to apply greater consistent power, which leads to a faster and more competent cyclist.
A schematic showing some of the skeletal muscles of a Homo sapiens. The schematic was based on an image in the book “The human body” by Linda Gamlin
(Licensed under Wikimedia Commons https://commons.wikimedia.org/wiki/File:Skeletal_muscles_homo_sapiens.JPG)