If you grew up with a bicycle as your primary mode of transportation, cycling is probably second nature to you as a relaxing, enjoyable activity. However, cycling can also be an effective exercise, both for your cardiovascular health and for your muscular strength. Though cycling may not strike you as a particularly intense muscle-building activity, you'll find that cycling can help strengthen muscle groups across your entire body.
The quadriceps are perhaps the most obvious muscle group affected by cycling; when you're tired and your thighs hurt, that is your quadriceps' way of signalling fatigue. As the name suggests, the quadriceps is a group of four muscles, and cycling benefits these muscles because the activity requires knee extension and hip flexion, for which the quadriceps provide the force. Strong quadriceps help you cycle more quickly and tackle hills more easily.
The encouraging phrase, "get your butt in gear" can apply literally to cycling, as the muscles located in your rear end -- also known as the glutes -- play a key role in cycling. Your glutes perform the task of hip extension, which is the movement of your thigh from a position perpendicular to your trunk to a position parallel to it. This movement occurs every time you pedal a bike and contributes a significant amount of the force to propel you forward.
It's often said that for every action, there is an equal and opposite reaction. This helps explain the relationship between your hamstrings and quadriceps, because they perform opposite roles. While your quads extend your knee and flex your leg at the hip, your hamstrings -- located on the back of your thigh -- perform knee flexion and hip extension, rounding out the pedal strokes that your quadriceps begin.
Each of your calves is comprised of two major muscles, the gastrocnemius and soleus. These muscles help move your ankle joint, and they receive special attention during hill climbing. Thus, cycling can help you build calf muscle size and strength.
If you're looking to strengthen the muscles that make up your six-pack, then cycling is for you. Core muscles such as your abdominal and lower back muscles improve the efficiency of your cycling by stabilizing your body and eliminating wasted side-to-side movement.
Cyclists tend not to have huge, hulking arms, but that doesn't mean your arm muscles won't derive a benefit from cycling. Cycling tends to build muscular endurance in your arms, as these muscles are engaged in maintaining a static position to support your body against bumps and curves in the course.
As with your arms, the primary benefit for your shoulders is an improvement in muscular endurance. Your shoulders help support your upper body when cycling and work with your arm muscles to prevent extraneous movement that wastes your energy.
Brian Willett began writing in 2005. He has been published in the "Buffalo News," the "Daytona Times" and "Natural Muscle Magazine." Willett also writes for Bloginity.com and Bodybuilding.com. He is an American Council on Exercise-certified personal trainer and earned a Bachelor of Arts in journalism from the University of North Carolina.