Last month we talked about how time on the erg can be used not just for physical training but also to improve one's technique. First though, you want to be sure the erg is set up for you.
Find a setting that feels right. A common drag factor range is between 120 – 135, which usually correlates to 3 to 5 on the fan setting. Use that as a guide, but don't feel obligated to stick to any exact number. Some people prefer to row a higher rate with a lighter load, others prefer the opposite.
Next, adjust the heel cup height on the foot stretcher. The tendency is to position the heel cup to allow the strap to fit comfortably over the ball of the foot, but if you have a particularly small foot, the heel plate ends up being way too high, making it difficult to get to full compression, i.e., where the shins are vertical. If you can't reach this position, try lowering the heel plate.
Shins vertical at the catch
Conversely, others find it easy to go beyond shins vertical, putting them in a weaker position and one that can be stressful on the knees. To prohibit this, you can stick a piece of thick tape or another item on the frame at the point where you reach full compression. Once you feel the seat hit the object, it's time to reverse direction.
One of the most common problems on the water that can easily be adjusted on the erg is the grip. Due to fear or whatever factor, many death-grip the oar handle. (If your forearms cramp when you row, that's a sign you're holding on too tight.)
Since there is no chance of flipping on the erg, relax and move your grip so that only the fingers are in touch with the erg handle, not the palm of the hand. (The thumb can hang loosely around the bottom of the handle) The fingers should work more as a hook and provide a direct connection for the body to connect to the handle. The wrist should be flat. When the grip is too tight, often the arms get tight, and instead of connecting to the lats, the tension goes up into the shoulders. Relax the grip, keep the arms loose, and try to feel the connection to the lat muscles.
Loose arms, loose grip, no tension in the shoulders
You can also work on hand levels on the erg. There are no wakes or balance issues to worry about, so no reason the hands shouldn't stay level on the drive and the recovery. One trick is to put a small piece of tape horizontally on the erg where the chain feeds in. Since you aren't actually catching and releasing a blade on the erg, I would recommend not changing the hand levels between the drive and recovery, but instead try to keep the chain level throughout the stroke. The piece of tape will help you to see how well you are able to do that.
The reason I suggest not changing the hand heights from recovery height to drive height is that the huge majority of rowers over do the up motion at the catch - causing the blade(s) to go too deep - and then press down too low on the recovery - allowing the blade(s) to come too far out of the water, which can lead to serious set issues.
A 40-minute workout on the erg will likely produce 800 to 1000 strokes. Think of all the good muscle memory you can build over the winter if you just keep doing the right thing over and over. Getting back on the water in the spring will be a snap! Erg hard but erg smart.