Rest days are important in lifting weights, my other hobby. It gives your muscles time to repair and grow. Without rest days you'll plateau and be stuck where you're at. Try drinking a creatine drink after you ride and be sure to load up on lots of protein. This helps your muscles recover and rebuild. I'm making gains in my cycling at a phenomenal rate and think my diet (lean meats, eggs, raw fruit, raw vegetables, etc) and my protein shake and creatine supplementing are the reason why. Yeah I'm still heavy but I'm packing on the muscle lifting weights and the cardio/endurance gains I attribute to my cycling. Now if I could quit smoking I could likely make some more gains.