The large thigh muscles, quadriceps and hamstrings, are the major players. The gluteus maximus, smaller muscles throughout the pelvis and the calf muscles, primarily the gastrocnemius and soleus, also help push the bike down the road---or up the hill, as the case may be. Muscles that act on a single joint are generally used in only part of the pedal stroke, while those that act on two joints are used throughout (though playing different roles at different times). For example, the hamstrings act both to flex (bend) the knee and extend (straighten) the hip, which both occur in a given pedal stroke. The gluteus maximus, on the other hand, works only to extend the hip and so is used almost exclusively during the downstroke.
Balance, stability and posture
The 'core' (torso) muscles are crucial for maintaining balance and for keeping your riding position solid. Most of these are muscles that you may not even know you have, much less be aware of when they're doing their job. Major muscles in this group are the rectus abdominis, the internal and external obliques, the transversus abdominis and the paraspinous (next to the spine) muscles. A strong core helps align the ribs, spine and pelvis and is key for most athletic activities. Cycling won't give you six-pack abs, but will help tone your entire core.
Steering, braking and cornering
The arms, forearms and shoulder girdle are critical for steering and braking. Muscles in the upper back and neck keep your head and spine facing forward so you can see where you're going and avoid obstacles. In addition to muscles needed for forward propulsion, cornering calls on the core muscles, the gluteus medius and minimus, and lower extremity muscles that don't otherwise contribute much.
Muscle roles during seated climbing are much the same as when riding on a flat surface, though there are some changes in biomechanics that can lead to more rapid muscle fatigue. This is especially true for climbing in a standing position, which causes shifts in muscle use due to the legs needing to support the body's weight in addition to providing power. Standing climbing also causes added stresses on the core, arm, and shoulder muscles, partly due to increased side-to-side bike motion.
Don't forget the muscle that powers the entire body: the heart. Cycling, like any aerobic activity, improves cardiovascular health. Benefits of regular cycling include reduced resting heart rate and blood pressure, weight loss and reduced body fat, improved cholesterol levels and reduced risk of diabetes.
Article Written By Peggy Hansen
Peggy Hansen holds a Bachelor of Science in biology from UC San Diego, Doctor of Medicine from UCLA, and completed postgraduate training at Stanford, Duke and Harvard. An award-winning writer and photographer, her work has been featured in Catnip, Herbalgram, Porter Gulch Review, and many online pieces. She's also a commentator for KQED-FM