For free speed, bounce less!

In rowing and paddling sports, our goal is to move through the water as quickly as possible with as little effort as we can manage. The bio-mechanics of rowing and paddling are incredibly complex, but one of the principles that has emerged is the importance of horizontal motion through the stroke, thus minimizing the vertical movement of the boat. This turns out to be important for two different reasons.

First, it seems intuitive that if our goal is to move horizontally through the water, then any energy spent in lifting the boat during the drive is effectively wasted. This is why blade depth is such a point of emphasis in rowing. By maintaining a horizontal drive motion with the blades just under the water, we maximize the amount of energy propelling the boat toward the finish line.

The second reason to “row horizontally” (and minimize vertical motion) is a little more subtle and has to do with the relationship between hydro-mechanical drag and boat speed. It turns out that the amount of drag through the water is related to the square of the boat speed. In rowing and paddling, boat speed necessarily varies over the course of the stroke (although less so for kayaking). Because of this, and the relationship between speed and drag, it follows that minimizing this speed fluctuation will yield the minimum average drag. This is because the drag penalty we pay when we’re faster then the average speed is much greater than the drag benefit that we reap when we’re slower than our average speed.

Since drag is also directly related to the amount of hull surface in contact with the water, it stands to reason that we would want to keep this constant as well, since that will make it easier to minimize our speed variation.

For a more comprehensive discussion of these concepts (and much more!), see this article by Volker Nolte on the World Rowing website. While this article is specifically about rowing, many of the principles apply to paddling as well.

How CrewNerd can help!

While CrewNerd uses your phone’s accelerometer primarily to determine your stroke rate, it also calculates the vertical component of your acceleration (regardless of your phone’s orientation, by the way), and uses this to compute a metric based on your vertical motion, called “bounce”. This little-known feature gives you the feedback that you need to improve several aspects of your technique.

To see your “bounce”, just select it as one of the data fields on the Row/Paddle screen. Bounce is basically a measure of your vertical movement as you row, ignoring a certain amount of motion which is unavoidable. The number that CrewNerd displays is actually an average over your last five strokes to avoid focusing too much on any one stroke. It’s the longer-term trends that are more meaningful.

People often ask about the unit of measurement for “bounce”, but it’s really impossible to answer that in a satisfying way since the calculation is rather complicated. It’s probably best to think of “bounce” as a measure of energy – i.e. the amount of energy being expended to “lift” the boat unnecessarily, or the amount of additional energy required to maintain your speed due to drag variation. However you think about it, lower is better, but don’t feel compelled to get the number to zero, since that will never be possible.

But how can I reduce bounce?

In rowing, several different technical flaws can lead to increased “bounce”. Some of the things you can focus on to reduce your bounce number include:

  • Maintaining good blade depth
  • Maintaining good hip posture at the finish – i.e. keep your hips upright to avoid letting your center of gravity drop as you release the blades from the water.
  • Lift your hands into the catch – if you avoid “skying” your blades before the catch, this will help prevent problems with blade depth on the drive
  • Don’t lunge at the catch, as this creates downward momentum that will make the stern drop lower in the water.

How should I use “bounce” during my workouts?

Because many different factors will influence the bounce calculation (boat size and weight, rower weight, water conditions, etc.), it isn’t generally useful to compare raw bounce numbers between boats, or even the same boat in different water & wind conditions.

The best way to use the bounce feedback is when working on technique within a single workout. If you’re working on blade depth, for example, look at your bounce numbers before and after doing some drills to see if you can make an improvement. During a long piece, take some “focus 10’s” to work on posture at the finish, or lifting your hands into the catch, and see if you can see an improvement in your bounce number.

Several CrewNerd users have written us over the years to say how much they’ve come to rely on the “bounce” and “check” numbers to improve their technique – especially folks who don’t have the benefit of in-person coaching. The next time you’re on the water, give it a try and see what you think.

[In a future post, we’ll talk about bounce’s cousin, “check”.]

Comments are closed.