There are quite a few excellent forearm exercises, and this is definitely one that can give a great forearm workout. It is based on what an otherwise average size guy I once knew did to develop gigantic forearms.
The first job I had with an hourly wage was as an appliance repairman’s helper. It was the first time I saw a real person whose forearms looked like Popeye’s. Until this guy I thought Popeye was just a cartoon character. He spent much of his day using a screwdriver. This was before battery-powered screwdrivers or power drills. There was just the plain wooden handled variety. And there was no drilling a pilot hole for the screw. You just placed the screw next to the wood and started turning. Wimps like me scraped the screw on a piece of soap first, so it went into the wood easier. But this guy just started turning – no wimpy coating on the screw. He could just go from one screw to the next with no rest and just keep on going. And did he ever have huge forearms.
No, you don’t need to get pieces of wood or a bunch of screws. You can simulate the same motion using a dowel of wood or a metal bar with a diameter about the same as a screwdriver handle or even a little narrower. In this case, the smaller the diameter, the harder the work. Remember the lever math problems you did in high school physics? The handle of the screwdriver is a lever and the wider the handle, the easier it is to turn.
Get a wooden dowel or metal bar, a strap or rope and a weight, such as a weight plate, kettle bell or bucket of sand. If the dowel is 3/4 to 1 1/4 inch diameter, it will be about right, but you can experiment with the diameter. You can use a wider diameter, but it will be easier to turn with the same weight.
Tie the strap (or rope) to the weight and then secure the strap around the dowel. Place one end of the dowel on something between elbow and shoulder height and then start turning until the plate reaches the dowel. Then unwind and rewind, continuing until your forearm is screaming. Then do the other forearm. You can then return to the first forearm and turn the dowel in the opposite direction. This way you work both the pronators and the supinators.
The higher the suspension, the longer you can go until the weight reaches the dowel. I like to stand on a bench and place the dowel in a hole in a power rack. But you can do it with one end of the dowel on a deck or retaining wall, table, ladder rung or any suitable support and yourself on any safe surface.
You can do as many sets as you feel appropriate. If you want to be like the Popeye I worked with as a kid, you can do it several times a day for several years, and you don’t even have to know how to repair a refrigerator or air conditioner.