What are "check" and "bounce"

CrewNerd uses the accelerometer in your phone to detect strokes and measure your stroke rate. But the accelerometer can also be used to analyze the quality of your strokes based on the motion of the hull. CrewNerd provides two quality metrics that we refer to as "check" and "bounce" that are computed by examining the data we get from the accelerometer in novel ways.

What is "check"?

Check (or "stern check") is a term that most rowers are familiar with. Wikipedia defines check as:

The amount of interruption of the forward movement—usually occurs at the catch and sometimes at the release.

We experimented with many different ways of measuring "check", looking for an approach that would most clearly distinguish between good and bad rowing. In the end, what worked best was to measure the consistency of the hull's deceleration during the recovery, and this became our "check" metric.

Check is always averaged over the last five strokes, because we never want to focus on one bad (or good) stroke. The goal is consistent improvement.

What is "bounce"?

While "check" is based on the horizontal acceleration of the hull, we can also learn much by considering vertical movement. Physics shows that boats move most efficiently when the amount of wetted surface remains constant. It also seems intuitive that any energy spent lifting the boat vertically is wasted, since the goal is to propel the boat forward.

The "bounce" metric effectively measures excess vertical motion during the stroke. In practice, we find that this rewards good posture at the catch and release and penalizes you if you "collapse" at the finish.

As with check, the bounce metric is averaged over the last five strokes.

What are good check & bounce numbers?

Customers sometimes ask what a good number would be for check or bounce, and it's really impossible to say. The actual numbers are influenced by so many factors including the size of the boat, water and wind conditions, and so on.

Instead, we recommend using these metrics as a tool combined with drills that focus on different aspects of technique. Take a few strokes to focus on hip posture at the release and see if you can lower your "bounce" number. Or spend some time working on your catch and see if you can reduce your "check".

Over time, you'll learn what "good" numbers are for you, and the metrics can be a way to see when your technique may be slipping in one way or another.