>>1323088/fit/ here
That's where you're wrong. Muscles increase in size from the body repairing micro-tears in the muscle fiber and healing over time. Therefore, ANY exercise that strains a muscle past baseline will help increase muscle mass. Too much strain, however, will cause injury and longer recovery time.
Yes, sprinting faster will increase muscle mass, but you can also increase muscle mass by mashing away at the pedals on a single speed. Sprinting is better at cardio and stamina, but less effective for muscle mass.
Sprinting fast also requires lots of space and good terrain. However, you could get almost the same amount of work going up a small hill on a singlespeed.
