This comes from former student and old friend, Tom Greenberg.

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.