After a couple of weeks, move up to 10-lb potato sacks. Then try 50-lb potato sacks but don't rush the program; take your time. Lastly, try to get to a point where you can lift a 100-lb potato sack in each hand and hold your arms straight for more than a full minute.
Once you reach this level, put a potato in each of the sacks.
This program is not patented nor under copyright, feel free to use it.