Not when done properly. Many people think that adding resistance to your bike will bulk up your legs. This is not true. The more resistance you use, the more lean and defined your muscles will get. Think of it like this, look at a long distance runners legs and compare them to the legs of a sprinter. The sprinters legs are huge! Why, because they run short distances, at high speeds. A long distance runners legs are very lean because they pace themselves. So, remember to “TAP IT UP”.