Begin by standing on a comfortable surface, where you have plenty of room at each side.

With a 2kg. 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 5kg. potato sacks.

Then try 15kg. potato sacks and then eventually try to get to where you can lift a 40kg. 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!