Fr Z's original title: Can I workout on Sunday?
Let’s turn first to the Catechism of the Catholic Church:
2185 On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord’s Day, the performance of the works of mercy, and the appropriate relaxation of mind and body. Family needs or important social service can legitimately excuse from the obligation of Sunday rest. The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health.
So, provided that you are still performing your religious duties according to the 1st Commandment of the Church (i.e., attend Mass on Sunday and Holy Days of Obligation), you can (fill in the blank)...
In general, we should avoid strenuous work on Sundays. A “work out” is, by definition, “work”, but of a different kind than most labor. First, though it is hard, we derive a real good and satisfaction from it. By working out, you are caring for your body, which is your responsibility before God to do. Source
With Fr. Z advice I guess you can convert your AR's to California Compliant on Sunday