Rowing on a machine is very similar to rowing on the water, but also very different. The basic bodily motion is (or should be) the same. But on the machine you are only moving back and forth but you are not moving through space. You are not dealing with balance. And you are not interacting with the surface of the water.
One model you can follow to pay attention to what you are doing as you row is to focus on the points of contact. On the erg there are three, feet in the foot stretcher, seat on the seat and hands on the handle. On the water, there are two more.
Consider the (outdoor) rowing motion from the perspective of points of contact among the body and the equipment and the water. It is through these points of contact that your bodily effort moves the boat. You are sitting down and yet you are moving. You are facing backwards and yet you are going forward. You are moving your body back and forth and yet the boat moves continually ahead. The blades of your oars repeatedly drop into and lift out of the water and yet you stay balanced. The blades push against a fluid and yet they propel your solid boat and body across the water. How does each of the five points of contact enable you to make this happen?
The five points of contact are the points where your body touches the equipment and the oars touch the water:
- The foot stretcher, where your body is fixed to the boat;
- The seat, where your weight rests and on which you move back and forth;
- The handles, the link between your hands, the boat and the water;
- The oarlock, the fulcrum against which you lever the boat forward with the oars; and
- The blades, the instrument with which your bodily effort swings the boat forward.
Next time you are in a boat, select one of these points of contact and consider, as you row, what part it plays. Here is one image to start with: Imagine you and your single are floating not on the water but in the air. You are a unitary physical system, of which the boat is about 30 pounds and most of the weight is your body. If you were floating on air (and are ignoring rowing/forward motion for a moment), each movement you make back and forth with your body would involve a corresponding opposite motion of the boat. And, since your body has more mass, the boat would move a correspondingly greater speed or distance to maintain equilibrium. Apply that to taking a stroke; as you glide through the recovery, the boat must surge forward, not necessarily because you are pulling it forward with your feet, but simply because the weight/mass as a whole will have consistent momentum – and as you reverse (actually just slow) the forward momentum of your body, that must necessary speed the forward momentum of the boat.