What muscle GROUP would you use for cycling?
All them, but the legs and buttocks do most of the work in
cycling.
Here are the groups, (quadricep) this straightens the
leg,(hamstrings)this muscle bends the leg,(gluteals) these are your
buttocks and the(gastrocnemis and soleus) are your calf
muscles.
If you're riding well hunched over you'll bring your abdominals
and back muscles into play to some degree as well. Riding out of
the saddle will engage arms and shoulders too.