For those of us getting along in years, here is a little secret for building your arm and shoulder muscles. You might want to adopt this routine. Three days a week works well.

Begin by standing outside behind the house, with a 5-LB potato sack in each hand.  Extend your arms straight out from your sides and hold them there as long as you can. Try to reach a full minute.  Relax.

After one week move up to 10-LB potato sacks, then next week 50-LB potato sacks, and eventually try to get to where you can lift a 100-LB potato sack in each hand and hold your arms straight out for more than a  full minute.

After you feel confident at that level, start putting a couple of potatoes in each of the sacks, but be careful not to overdo it.