Cycling is one of the most popular sports in the world and it is estimated that there is over 4 billion bikes world wide now. The motivations for cycling vary, from just wanting to get a bit of fresh air, to wanting to dramatically enhance your fitness. Generally speaking the type of cycling you do will affect how your muscles will adapt. Cycling for long periods of time, but at reasonably low force, will encourage your muscles to build slow-twitch fibers and improve their endurance levels. On the other hand, if you cycle hard and fast, your muscles will build fast-twitch fibers and become more powerful. But which are the muscles that are demanded the most of when riding.
Quadriceps (thigh muscles). The muscles that are worked the hardest whilst cycling and so need to be the most developed are the quads. These are the muscles that straighten out the leg and produce the down force on the pedals, which in turn rotate the crack. Racing bikes in fact are designed to locate the quads directly over the crack so that maximum efficiency is achieved. When cycling fast, these muscles are contracted and relaxed hundreds of times a minute and so they need to be in good shape.
Gastrocnemius (calf). The calf muscle is a great deal smaller than the quads, but no less important when it comes to propelling the bike forwards. Flexing the calf muscles when the leg is in a straight position, points the toes towards and adds a small boost to the overall power output. Pinarello make pedals that dynamically pivot to squeeze every last bit of power juice from the calf muscles.
Hamstrings. Whist the quadriceps provide the downward power that propels the bike forwards, it is the hamstrings (back of the legs) that work to bring the leg back up into a flexed (bent) position. This doesnt require much force on a standard bike as the rotation of the pedals pushes the leg up but when you use cycling shoes that clip to the pedals, a large amount of additional force can be generated by these muscles in the upward movement