For those who have spent their teenage years in front of the TV, here is a little secret for building arm and shoulder muscles. Three days a week works well.
Begin by standing outside behind the house, and with a 5-LB. potato sack in each hand ... extend your arms straight out to your sides and hold them there as long as you can.
After a few weeks, move up to 10-LB. potato sacks and then 50-LB potato sacks, and finally get to where you can lift a 100 lb. potato sack in each hand and hold your arms straight for more than a full minute.
Next...start putting a few potatoes in the sacks, but be careful not to overdo it.