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Push harder

with our seat sensor

· seat sensor,rowing

To make the most of your legs you need to stand on the stretcher when pushing off each new stroke. The better you hang from the handle, and the faster you push with your legs, the more force you use to propel the boat forwards via the blades of your oars. With our Rowing Performance App and sensor you can measure the speed of the seat during drive and recovery.

The below shows an example of what we can measure with our seat sensor. The graph shows the seat speed during one stroke of two rowers in the same double, the red is a that of Pentti, the guy I am rowing with and the green shows my rather flatter curve (I'm a LW woman). We were rowing in the same Finnish style double boat earlier this week in the cold sea outside of Helsinki, our 1st outdoor rowing in Finland this year!

The seat speed is shown in meters per second on the y-axis and the x-axis shows the time of one stroke. Here the stroke rate was 25 meaning that the time of each stroke was a bit less than 2.5 seconds.

The seat speed of two rowers in the same boat during one stroke . Differences in speed magnitude but the rhythm matches quite nicely

There are clear differences in the magnitude of the speed during the drive, when the seat speed is positive, when the legs are straightened and the seat moves towards the bow. Ideally the legs should accelerate through the stroke but as seen above my own seat (green curve) starts to slow down already very early during the drive. Pentti's seat (red curve) accelerates nicely to about 1m/s peak velocity and reaching the far position before me. What's nice however is that our seats remain stationary until we both start recovery at the same time. Having the same rhythm is crucial in a crew, you should not have one rower racing up the slide before the others, that only upsets the flow of the boat...Synchrony is needed to move the boat efficiently and overlapping the seat speed curves from rowers in the same boat is a nice way to check whether the crew is rowing with the same technique. Speed of seat movement is of course interesting but so is the shape of the speed curve and answers to questions like these:

  • how fast does the seat change direction at catch?
  • is the seat stationary long enough at the back stop?
  • does the rower make use of trampoline effect when approaching the stretcher?
  • at what moment of the leg drive does the peak leg velocity happen?

But most importantly, do rowers in the same boat move their seat in the same way?

Our App defines the beginning of the stroke at the minimum of the boat acceleration and divides all measured data into stroke sized chunks from each acceleration minimum to the next. The below graph shows the acceleration of the boat (the solid line) during one stroke (the dotted line shows how the boat velocity varies during one stroke). The y-axis shows the acceleration in m/s^2 whereas the x-axis shows the normalized time without units, the x-axis is auto-scaled to fit one entire stroke cycle, no matter the stroke rate, just like the seat speed graph. The shape of the acceleration curve as well as the max and min values depend very much on the rowing technique . If the y-value is positive it means that the boat is speeding up, and you can easily see during which part of the stroke this happens by having a look at what part of the curve is above the x-axis.

The boat acceleration during one stroke, we define the beginning of the cycle at the acceleration minimum. During catch the acceleration is negative but it becomes positive during the drive and is more or less zero during recovery.

We define the beginning of the cycle to be the moment the boat reaches its minimum acceleration and that happens more or less at catch, but whether or not the boat acceleration minimum happens exactly at catch or slightly before or after really depends on the rower. Catch is defined as the point where the oar changes direction from recovery to drive and we can measure that too with our sensor but this blog is about the seat so let's get back to the topic at hand. As you can see from the seat graph on the top of this page the seat speed changes sign from negative to positive already before the boat acceleration minimum, I mean that the seat speed is already about 0.25m/s at the beginning of the cycle at the starting point. We are not coaches and will not say if this is good or bad, but we can say that it is beneficial that both rowers in our crew move in the same way.

Check out our Rowing Performance App and Sensor if you want to measure the speed of your leg push. Of course there's more to rowing than seat movement. Long efficient strokes move the boat and for that you need also your trunk and arms. Our sensor can measure not only seat movement but also the oar and more specifically the full stroke angle and the flight path that the oar makes each stroke, I'll write more about that in my next post.

Happy that the rowing season started in Helsinki this week. It means lots of rowing but also that publishing posts like this with fresh analysis on how our sensor and App can help improve rowing performance is much easier for the next 6 months ;-)



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