About a month ago the health club at work gave me a session with a personal trainer as a birthday present. I choose one of the trainers who is also a good cyclist and explained to her what my activities were as well as my goals. She put together a 1 hour routine to work muscles that will balance my cycling - mostly to strengthen my back (upper and lower), abs and one for parts of the hips and thighs that cycling does not work hard. I cut out my dedicated hill climb night (moved the climbs to my weekend ride) and lost one of my two off days to fit these workouts in.
Week one was rough, week two a little better but still for two days after each session I walked around like an old man (Hey - I resemble that remark). This week is much better but still a little sore.
The interesting part is that I could ride just fine, the stiffness did not hurt my cycling, what these exercises were working were not heavily utilized while cycling. This morning on my training ride, my riding partner wanted to do a hard workout with some fast intervals, I felt my riding was better even though I was tired and would have rather had an easy ride. I was even able to do the hill sprints in the big chain ring.
I hate working out in the gym, but the outcome may be well worth it. I know some others here mix up their fitness routines. So far I am pleased with what I feel is happening. I would recommend it to others.