The key word is strength training. If you're doing it correctly you're not going to gain 50lbs of solid muscle mass. Instead you'll gain lean muscle which should only improve your cycling abilities. I also have a bowflex I use twice a week. I've noticed gains in my cycling abilities from minimal leg workouts on it. I do leg press, leg ext, leg curls, 4x20 each. More sets/reps of lighter weight is what i've always knows as strength training vs less sets/reps of heavier weight for mass building.