If you want to look like you are starving to death, stick with cycling. If you want to have some muscle and be strong all over, cycle AND lift weights. Cycling is a great cardio workout and I wouldn't give that up...but you don't have to only cycle. As you get older, the importance of resistance traing increases. Have to keep the muscles active. BUt remember, you can't lift weights at 40 the same way you did at 20. Stuff starts to break.