Begin by standing on a comfortable surface, where you
have plenty of room at each side. 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, and then relax. Each day
you'll find that you can hold this position for just a
bit longer.
After a couple of weeks, move up to 10-lb potato
sacks. Then try 50-lb potato sacks and then eventually
try to 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. (I'm at this
level.)
After you feel confident at that level, put a potato
in each of the sacks.