Some of you may know that I have been working out with my brother. He's very knowledgeable about working out and such, but I was wondering if you guys had any suggestions. He's been working out for about 6 years now, and hasn't gained much leg mass, he has very skinny legs that he would like to gain some muscle. Today at the gym he was talking about how he needed to start doing cardio. I post here to ask you question if there is anyway he can ride bikes with me for cardio, gain leg muscle, and not lose much weight if any. Hills? Hard constant stand-up peddling? Any suggestions are welcome.