For relief of tired muscles I'd suggest (after taking to your doctor in regard to a health check in case there's some other matter that needs to be considered,)

For relief of tired muscles I'd suggest (after taking to your doctor in regard to a health check in case there's some other matter that needs to be considered,) purchasing some pure 100% unflavoured Creatine Monohydrate. Ignore the higher amounts for muscle building, or the initial loading - view it instead as a daily supplement, and take about a third to half of the rate given in directions for the first couple of weeks and then vary it accordingly. Note be mindful of how much you normally do in a day and try and stay at around that level of activity. I was using it about 30 years ago and encouraged my parents to try it out, not at high rates either, both stopped taking it after a few days as it gave them bad cramps - when I dropped by I discovered they were well and truly over-doing it (such as the daily weeding a fairly large vegetable patch) getting though what would have normally been done in a week, in a singular day. As for muscle mass, that's different, as people get older it seems unfortunately the skin gets thinner as well as losing some mass around muscles - when one is younger, inactive periods don't incur much muscle change as it does when we're older. There are new medications coming but they are either expensive or will need to pass tests for regulations.