There are numerous factors that make an individual’s rowing experience unique. These factors include a rower’s anthropometry, the weather conditions in which he/she rows, the depth of the water, currents and waves, the type of rowing shell, its rigging, the inboard/outboard and the stiffness of the oars used by the rower. Given so much diversity in conditions it is often confusing for a rower to know if his/her input effort is producing an output speed that is optimal.
In this article, I will talk about how input effort can be visualised in the form of graphical concept called the force curve along with output speed/pace to achieve optimal rowing speed.
Force in rowing is exerted by almost the entire human body behind the blades of rowing oars nicely pivoted in the water. This helps lever the bodyweight out of the boat and consequently reducing wetted-surface area as the boat float outs of the water and moves with low resistance. The force generated by the rower levering his/her body manifests itself in the form of an oar bend as shown in Figure 1.
The oar bend can be measured using the Oarzpot sensor developed by Sweetzpot, Norway. It is installed on the oar as shown in Figure 2. When the oar bends, the force is transmitted through the click-on buttons to a semiconductor strain gauge embedded within the sensor. The voltage across this strain gauge changes with varying forces experienced. This voltage is converted from an analog value to a digital value and transmitted over Bluetooth to the Sweetzpot Rowing App on iOS and Android.
The Oarzpot is first fixed to one of the oars. The sensor pairs with the Sweetzpot Rowing App and provides realtime feedback on the force curve as shown in Figure 3. The force curve is a graphical representation of the bend created in oar due to a rower’s input effort. The pace of the boat is the output (shown on the top left corner of the picture in picture) due to the rowers bodyweight behind the oar.
Does your force curve make the boat go fast? Everybody is made different, hence there is no straightforward answer to the question. A look at the realtime video (Video 1) reveals how fast one can go based on their current force curve and the peak force they are able to achieve.
Modifying the force curve should give the rower more speed for specific conditions. This varies with the environment and the dimensions and stiffness of the oar being used. A general rule of thumb is to try to achieve high peak power as soon as the blade is in the water. This gives great speed to the boat but at the same time is energy consuming. This idea of aiming to generate a peak force is illustrated in Figure 4. The rower is expected to push the envelope from the black force curve to the red one. Generating such a high peak force at a low rate (18–20 spm) is relatively hard but a rower must strive to achieve it with good timing at the catch and quick loading of the blade with his/her bodyweight.
Aiming to achieve the peak force as shown in Figure 4 maybe quite challenging. A high bend in the oar also means that the boat is not moving (as it offers resistance to the oar), although the oar straightens out or ricochets back eventually. This depends also on how stiff the oar really is. A soft oar will bend much more than a stiffer oar. The bend is also affected by how strong a rower is and it able to apply force as soon as the blade is in the water. The resistance force on the oar is higher when the boat goes faster due to the resistance offered by the higher skin drag experienced by the moving boat (if v is the velocity of the boat, then the skin drag is proportional to v²) . This means the faster you go the higher and quicker you will peak in the force curve to compensate for the skin drag. World class rowers can achieve speeds of up to 15 kmph at a low stroke rate of 18–20 strokes per minute. This level of physical fitness allows them to go up to 17–18 kmph in a single scull for a 2000 m race. For a club level rower a speed of 13–14 kmph at a low rate would be quite an achievement under no wind and flat water conditions.
We believe that keeping the general rule of thumb in mind it is important for a rower to explore force curve patterns that helps generate the maximum boat speed within the expected heart rate range. And, repeat the pattern. I would imagine that a rower will have different force-curve based tactics to make the boat go fastest in head wind, and tail wind conditions.
An aspect of the force curve worth fixing is avoiding negative forces at the finish. These negative forces may be experienced due to the oar getting stuck in the water and not having a clean extraction.This can be seen in Figure 5 where there is dip below the baseline at the finish indicating that the blade is stuck at the finish and the rower is washing out without a clean extraction.
I have also seen that many people have a two-piece rowing stroke displaying a discontinuity between the transition from the push of the leg to the use of the arms as shown in Figure 6. One way to fix this is to use the breathing muscles as a conduit to lever the entire body so that the legs and arms not segregated in their usage. I believe that the two-piece stroke originates at the finish when the rower exaggerates the finish without have constant pressure (due to body leverage) behind the blade. If the body is levered properly then there would not be the two-piece stroke.
I have been trying to coach people to transform a two-piece stroke to a smoother stroke (Video 2). This is often quite a challenge given that many rowers learn to divide their rowing stroke into the use of legs, back and then arms. This has to be unlearnt and rowers must be taught relatively quickly the use of the breathing muscles and use their entire body as one entity after an initial breakdown.
A previous member of the Norwegian national rowing team also experimented with the Oarzpot as shown in Video 3. His main revelation was the fact that he needed to improve his peak force at lower rates. However, he generated tremendous length and power at higher stroke rates (see 10 seconds into the video). The force curve approaches the ideal curve and his speed exceeds 17 kmph at a higher stroke rate of 38 spm. It is an incredibly high stroke rate but will the rower be able to keep the speed and rate for the entire length of 2000m. He also had some balance issues that accumulate over the course of 2000m. We collectively understood that it might be worthwhile if he focuses on increasing boat speed at a lower rate and push his baseline speed up to 15 kmph at 18–20 spm under no wind and flat water conditions.
Visualising the force curve is an interesting tool to help rowers improve their boat speed dramatically. At least, it has helped me personally a lot to put theory into practice. In particular, focusing enormously on levering my body weight from catch to finish. I also realised the need for weight training, reducing my body weight to stay levered for the maximum amount of time per stroke. I wish I had such insight when I was 10 years younger, but its never too late to discover oneself.
