Understanding check and bounce

SpeedCoach Mobile uses the built-in accelerometer in the iPhone (and iPod touch) to accurately measure your stroke rate. But the accelerometer is capable of much more. With it, SpeedCoach Mobile can also calculate metrics that provide insight into the “quality” of your rowing. It does this through two separate metrics – “check” and “bounce”.

The first of these (check) is well understood by rowers and coaches, but can be described and measured in many different ways. After much experimentation, we found that a useful way to think about check is to consider the smoothness of the recovery.  During the recovery phase, the rowing shell naturally decelerates. However, irregularities in the natural deceleration can be indicators of flaws in the stroke. Rushing the slide or driving with the legs before the blade is in the water both cause the natural (and gradual) deceleration of the boat to be disrupted.

In SpeedCoach Mobile, the “check” factor is an indicator of the consistency of your deceleration during the recovery phase of the stroke. The lower the number, the smoother your recovery. Higher numbers may indicate one of the flaws mentioned above. Many factors will naturally influence the check factor – boat type, stroke rate, power, water conditions, wind, and so on. It’s best to look at the check factor within the course of a single interval or workout. Comparisons from day to day will be much less meaningful. Within a single interval, you may find it helpful to experiment with your stroke to see what changes can lower the check factor.

To reduce the effects of any single stroke, the check factor is calculated as a running average over your last five strokes. This makes it easier to focus on long-term habits and trends that affect your rowing, rather than focusing on a single bad (or good) stroke.

The bounce factor is easier to describe. Bounce is just a measurement of the energy associated with the vertical displacement of the boat in each stroke, the idea being that vertical motion generally represents wasted effort. High “bounce” numbers may mean that you are lunging at the catch (causing the stern to dip), pulling through too high with the handles during the drive (lifting the hull), or not maintaining good posture at the release (causing the bow to dip). Like the check measurement, bounce is averaged over your last five strokes and comparisons from day to day or boat to boat are discouraged.

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