I work mostly the arms, trunk, calves (for Achilles' tendinosis), and medialis quad muscles (for kneecap tracking) 3-4 times per week at the local YMCA. This complements my cycling and fast walking. I finally got serious about upper body work after I broke my wrist 25 years ago and decided I needed to protect my upper body bone mass and density. I worked out about once per week for a long time, barely maintaining what little upper body strength I had, but since I started an encore career that lets me work at home on Tu and Th, I have been on a pretty regular 3, sometimes 4, day per week regimen, and I have been getting modest results.