Cycling is a low-impact exercise, and those who actively participate in cycling have about 10 percent more leg muscle than those who refrain from exercise.
Cycling outdoors provides the most challenging workout, but indoor cycling can also lead to stronger leg muscles and knees.
The two largest muscles that riding a bike targets is your quadriceps and your hamstrings. These muscles contract in a sequence that creates the pedaling action. The quadriceps and hamstrings do most of the work when you ride a bicycle.
How voluminous your muscles get depends on a host of factors including your height—shorter riders’ legs tend be, or a least appear, stockier; your genes—some people, like sprinters, have more fast-twitch “anaerobic” muscle fibers, which are the ones that really pop, giving track racers those Lycra-busting quads; and how and where you ride—spinning easy at a high cadence develops less muscle than pushing harder on those pedals.
“Cycling is a power sport,” says David Ertl, a USA cycling coach. “You need leg strength to crank out power. That means building all the muscle fibers you can. If you can get 10 or 20 percent stronger than the next guy or gal, you won’t fatigue as quickly and you’ll have that much more in reserve when you need to give a burst up a hill or off the line at the start.”
If you only sit when riding you will find that you are doing very little to foster muscle growth. After all, you are offering little resistance for your legs to power through, so they will simply tone up and build some level of endurance.
By standing you use your own body weight to add resistance, thus providing an excellent workout for your calf muscles in particular. Try riding slowly and raising your heels, all in the standing position, and you will find you apply more weight on your down-stroke, while also creating resistance using your body for the upstroke.
If cycling on a flat surface offers too little resistance for muscle building, it stands to reason that going uphill will remedy the issue. Gravity alone will force you to make more use of your leg muscles, taking them out of their comfort zone and forcing them to battle against resistance for the desired effect.
By riding uphill you are forcing both your bike and body against some resistance, allowing you to work on building your quadriceps and hamstrings. Do it enough and you will find that your muscles build up fairly quickly, allowing you to exhibit more power when you are riding on a flat surface.