With a 5-lb potato bag in each hand, extend arms straight out from sides & hold. Soon you’ll find you can hold this for a bit longer. Try to reach a full minute. Then move up to 10-lb bags, then 50-lb bags & eventually get to where you can lift a 100-lb potato bag in each hand & hold your arms straight for more than a minute. (I’m at this level) Once you feel confident at that level, put a potato in each bag.