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Row with the same rhythm

on synchronizing crew rowing technique

· seat sensor,Oar Sensor,rowing

How to make the boat go faster?

To maximize the speed of your boat you need not only a committed crew with fitness and big muscle but you need to align the rowing technique between crew members. This post is about how the Quiske Rowing Performance System can help rowers improve their performance and crews synchronize their technique.

Our Rowing Performance System consists of an App and an external sensor which can be placed on either oar or the boat seat. The App provides real time feedback and our web portal gives detailed post-training analysis allowing for spotting differences in the timing of the main sequences that the stroke consists of: the catch, the drive, the release, and the recovery. When differences in timings between crew members come to light the real-time feedback of our App can help rowers align their technique with that of the rest of the crew stroke by stroke while training on water.

To row a boat efficiently everyone needs to move with the same rhythm, this means for example equal acceleration during the drive, same rhythm in moving the oars, keeping the seat stationary the same amount of time at backstop, and moving the seat the same way during recovery. These are things our product can help with and below you’ll find more on what we measure and how it can improve your rowing.

What we measure and what you get out of it

First of all, the basis for all data is the acceleration of the boat which we measure using a phone firmly attached to the boat.

The phone running our App should be attached somewhere where the rower can see the real time feedback

Acceleration is the rate of change of velocity with the unit meter per second squared. From the measured acceleration, we calculate how the velocity of the boat is changing as a function of time. The acceleration and velocity of the boat fluctuate in rhythm with the strokes, constantly changing with a cyclic pattern. Our algorithms detect the rhythmic pattern of the strokes and divide the data into stroke size chunks. We define the starting point of each stroke at the minimum of the acceleration and that happens close to the catch (=where the oar changes direction from drive to recovery).

The boat acceleration during the period of one stroke is measured with a phone attached to the boat

The boat acceleration varies rhythmically as a function of the strokes with the boat reaching positive acceleration (=velocity increasing) during drive, and with deep deceleration when the oars enter the water during catch. The boat acceleration is directly proportional to the force that is acting on the boat at any time (Newton's second law F=ma). A detailed explanation on the forces at work on a boat during rowing can be found in the book The Biomechanics of Rowing by Dr. Valery Kleshnev. The shape of the acceleration curve during the period of one stroke depends on the rowing technique of the rowers as well as on the type of boat. It’s a very useful graph to analyze to gain more understanding on whether the boat is being rowed powerfully and efficiently.

How do we define the stroke?

We divide the data into stroke sized chunks of data from each acceleration minimum to the next. A stroke starts when the boat acceleration is at minimum which may be slightly before or after or exactly at the moment when the rower(s) change the direction of the oar movement, namely the catch. As long as the acceleration is negative the boat continues to slow down until the blades have locked on to the water before the drive starts. The boat is at its slowest when the acceleration reaches zero after the catch. Then the boat starts to increase in speed during the drive phase. What follows after the drive is of course the recovery phase where typically the acceleration is zero but can also be negative or positive for a while depending on how the rowers move their bodies. As the crew prepare for the next catch the boat starts slowing down (decelerating again) and the next cycle begins soon after that (at acceleration minimum).

The boat acceleration curve during one stroke, from one acceleration minimum to the next

Both the boat acceleration and velocity vary in a cyclic pattern as a function of the strokes. The velocity (dotted line) can be calculated from the acceleration (solid line) and are shown below (I left out velocity units from here for simplicity):

The above corresponds to the acceleration of a double scull. The curve starts at the acceleration minimum which normally happens close to the catch (direction change of the oars) but before full entry of the blade into water. The magnitude of the negative acceleration peak depends on stroke rate and boat type and the best crews tend to have a deeper but narrower peak. The acceleration reaches zero and peaks faster in better crews and at higher stroke rates. After the first acceleration peak there is sometimes a hump in the acceleration (like above) followed by a second peak caused by the trunk and arms of the rowers. Sometimes there is a little finish hump caused by the removal of the blade from the water. During the relatively long recovery the boat acceleration is normally close to zero but can become positive at the latter part of the recovery due to the redistribution of the center of mass when the rowers approach the stretcher before catch. During the last part of the recovery the acceleration becomes negative (red area, this is normally defined to be part of the recovery period) when the crew changes from pulling the stretcher to pushing it.

Phases of the rowing stroke

Let’s look at the phases of the rowing stroke in more detail, and dive right into what most likely is the biggest benefit with our App: comparing the stroke pattern of different rowers in the same crew. To row a boat in the most efficient way the strokes of rowers in the same crew need to be synchronized. More specifically the timings of catch and finish, drive and recovery and the seat movements of individual rowers in the same boat need to match. The rowers need to row with the same rhythm. Let’s look at the phases of the rowing strokes measured at the same time from the right oars of two rowers in a double.

The above graph shows the angular velocity measured from sensors placed close to the oarlocks of the two right oars in a double (see how to attach the sensor to the oar here).

The sensor is placed close to the oar lock (this shows the left oar, the post data was measured from the right oar)

The angular velocity is positive when the blade of the oar is moving in the drive direction and it is negative during recovery. The catch is defined as when the direction of the oar changes and as you can see from the below graph catch in this case happens not exactly at the boat acceleration minimum but slightly before it (we define each cycle to start at boat acceleration minimum). The oars are already moving in the driving direction when the boat acceleration was at minimum but the blade catches water properly only after this, as can be seen from the kink in the oar angular velocity during the early drive, at that point the angular velocity continues increasing but it increases slower. At finish the oar angular velocity decreases quickly and changes direction to go into recovery (during recovery the sign of the oar angular velocity is negative, i.e. it is moving in a direction opposite to the drive direction).

The oar angular velocity is positive during drive and negative during recovery. This shows the location of the catch and finish, i.e. when the oar changes direction of movement

What can we learn from the angular velocity of the oar during the time of one stroke?

Here’s a list of some of the things that we can quickly read from the graph

  • the rhythm: the ratio of drive vs recovery
  • the peak speed of the oar during the drive phase
  • the speed of hands away at finish
  • the timing of the catch (change of direction of the oars) with respect to the boat acceleration minimum
  • whether there is rushing on the slides during recovery

Most importantly, when overlaying the oar curves of the rowers in a crew you can see whether the motion of their oars are synchronized and if they row with the same technique. In our example case the crew consists of a man and a woman, and their differences in strength can cause big differences in the oar angular velocity magnitude and in where the peak occurs. But as we've stated before we at Quiske are not coaches but we merely measure and we think coaches can read much more from these graphs than we can.

The example above shows that the two rowers in the double have slightly different technique and timing. The green rower, the LW male Quiske team member Pentti, has an earlier catch and finish than the blue rower which is myself, a LW woman. There are differences in the speed of hands away at finish, the speed of the oars during the early drive and in the peak values of velocity. We both catch before the boat reaches minimum acceleration. The total oar angle of the two rowers has slight differences, 95 degrees compared with 97 degrees: the angle is measured for each stroke and it can be analyzed in detail together with the full oar flight path (the vertical and horizontal angles that the oar travels through during one stroke) in the Rowingperformance.com web portal where all recorded sessions are stored for analysis and comparisons.

Seat rhythm

There is more to the phases of the stroke than how the oar moves and next let’s look at what we can learn when placing our sensor on the seat. To measure the seat the sensor can be taped under the seat or alternatively it can be placed inside the slot in the ProW seat.

The sensor can be placed under the seat to measuring seat rhythm and speed

The below shows the seat speed of the same two rowers (green is the LW man and blue is the LW woman) in a double during one average stroke (the average was calculated from roughly 20 strokes).

What can you learn from the seat speed graph?

Let me list just a few things:

  • The maximum speed of the male rower (green) is considerably higher than that of the female rower (blue).
  • The seat of both rowers changes direction before the boat acceleration minimum
  • The green rower speeds up on recovery towards the finish, perhaps to make us of the so called trampoline effect.
  • The blue rower changes direction of the seat before the green rower
  • The green rower keeps his seat stationary for longer but there is a little hump occurring during the last part of the drive phase

Our crew has work to do to synchronize our seat movements, to make the boat move more efficiently.

This is my first post about our new Rowing Performance App and sensor and I’d love to hear feedback and questions. For food of thought I leave you with just some of the things that the Rowing Performance system can help with:the boat acceleration and the seat motion graphs help rowers ensure they’re letting the boats slide under them during recovery so that they won’t upset the flow of the boat. By looking at the timing of the seat the crew can get help with rowing in synchrony. The seat data also helps rowers focus on accelerating their legs through the full drive, and making a fast and strong synchronized push with their legs. The oar graphs help synchronize the handling of the oar, the speed of hands away and the full shape of the oar flight path (horizontal and vertical angles). It is also interesting to compare the full angle that each rower is able to maintain at different stroke rates during a session. Should the rower move their hands quickly away or pause the oar for a small moment after extraction? This might be a matter of taste but crucial is that everyone in the crew row the same way.

The comparison of rowers is done after the training session in our web portal but our App also allows for real time feedback, helping work on fine tuning the rowing technique while on water. The rower can choose to see graphs of oar angles or seat speed or to see simple numerical metrics which might be easier to digest while concentrating on rowing. For example, the real-time feedback on the stroke angle can help the rower make long strong strokes, every single stroke. The App can also show the maximum seat speed during each drive, helping the rower focus on pushing hard with the legs, every stroke.

The Quiske field testing crew consisting of Kristina and Pentti show their oar and seat graphs in the post :-)

Br,

Kristina

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