The body consists of fat and lean body mass. Lean body mass, or LBM, is basically every type of tissue other than fat. When you have a high lean body mass, you also have a low body-fat percentage and high amount of muscle. This is why lean body mass is often referred to as "lean muscle mass." Biking is an activity that comes with health benefits, but it does not build lean muscle.
Calories vs. Muscle
Strength training and cardiovascular training are two different types of exercise. When you strength train, you lift heavy weights for a series of repetitions in a short amount of time. When you do cardio, you perform repetitive movements over and and over again for an extended period of time. This causes you to burn calories, but not gain a major amount of muscle. Biking is a type of cardiovascular exercise, so that's why it does not build much muscle.
When you pedal a bike up a hill or increase the resistance on an exercise bike and stand while pedaling, you are forced to work your muscles harder. This still won't gain you a lot of lean muscle, but it will increase the intensity on your muscles. Couple this with the fact that you burn fat while working out and you will improve your muscle definition. The main muscles that get activated during biking are the glutes, quadriceps, hamstrings and calves.
Biking might not build much muscular strength, but it does build muscular endurance. This is the ability to perform consistent repetitions for an extended time frame against a light resistance. Muscular endurance comes in handy if you are a competitive or recreational athlete in cycling events.
For Your Health
Even though you do not gain lean muscle with biking, you do gain multiple health benefits. This takes place any time you do physical activity. Regular physical activity can help lower blood pressure, reduce triglyceride levels, increase good cholesterol levels and reduce feelings of depression and anxiety. The goal is to exercise for at least 30 minutes on most days of the week.
The best way to gain lean muscle is by doing strength training in conjunction with cardiovascular exercise. Strength training will build your muscles and cardio will reduce your fat. If you are trying to build your leg muscles, perform exercises like squats, leg presses, lunges, step-ups and deadlifts. Use the heaviest weights you can handle, aim for eight to 12 reps and do three or four sets. On the off days of your strength training, ride a bike outdoors or use an exercise bike indoors.