Slide Rules

The other day, I got into a discussion—again—with a friend who swears his dynamic ergometer is easier on his lower back. I say “again” because I get questions regarding the differences between stationary and dynamic ergometers all the time. We know that rowers have to move their body mass more on stationary ergs, which means their legs have to work more during each stroke. Other than that, though, everything above the belly button—hand movement, handle force and load on the spine—is the same for both types of ergometers. Yes, the added inertia forces on stationary ergs create extra torque on the lower spine. But it’s hard for me to see how this additional load is significant enough to cause injury. There are other differences worth noting. Overall load, which can be measured by one’s blood lactate level, is lower on the dynamic ergometer for the same power output. Fatigue is thus more pronounced on a static erg than on a dynamic at the same splits, and we know that fatigue has a relationship with injury. It’s also possible that the higher rates and short stroke lengths we see on dynamic ergs also may reduce the risk of injury. However, none of this conclusively explains my friend’s rationale for the dynamic. One possible explanation rests in the variations in technique used on the two machines. The data is scant on this, but I have observed that rowers on stationary ergs tend to initiate their upper body earlier as they apply force on the handle. This has a profound impact on posture and generates an extra strain on the lower back. More research is needed, but this might explain what my friend was feeling.