Force Curve Display

[old] bw1099 · Post by **[old] bw1099** » December 14th, 2004, 11:12 pm

I like to use the Force Curve display on the PM3. The y-axis is labeled "kg" and "lbs" and there are some tick marks. Does anyone know how many pounds or kg per tick mark? bw

[old] Byron Drachman · Post by **[old] Byron Drachman** » December 16th, 2004, 8:13 pm

I also like to use the force curve, and I would also like to know what the x-axis represents. It is a scaled representation of time, distance, or number of revolutions of the flywheel? Byron

[old] billrows · Post by **[old] billrows** » December 16th, 2004, 9:53 pm

Another question about the force curve. What is a good shape for a force curve? Mine has a big hump followed by a dip and then a short hump. Tks.

[old] Byron Drachman · Post by **[old] Byron Drachman** » December 16th, 2004, 10:46 pm

Hi Billrows, Mine looks very much like the picture shown at the Home Page <a href='http://www.concept2.com/products/pm3/pm3.asp' target='_blank'>http://www.concept2.com/products/pm3/pm ... except mine is smoother. It gets a little jagged when I'm very tired. Are you a little late with your finish? I'm pretty sure it's supposed to look like a gumdrop slanted to the left a little. Can you row strapless? Byron

[old] PaulS · Post by **[old] PaulS** » December 17th, 2004, 10:52 am

</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td class='genmed'>QUOTE (Byron Drachman @ Dec 16 2004, 04:13 PM)</td></tr><tr><td class='quote'> I also like to use the force curve, and I would also like to know what the x-axis represents. It is a scaled representation of time, distance, or number of revolutions of the flywheel? Byron  </td></tr></table> The X axis is Time, the reason the curve compresses to the left as speed increases. The force curve that is shown in the link, is not a bad example now that C2 has included more of the first part of the stroke. (Ver 82) Keeping the curve smooth and convex is a good rule of thumb, "Left leaning Haystack" or left leaning gumdrop (to use the C2 description). When a concave section appears, it is generally due to poor coordination of the drive sequence. The left lean should be due to good use of the legs to establish pressure, as they are the strongest muscles involved.

[old] michaelb · Post by **[old] michaelb** » December 17th, 2004, 1:33 pm

</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td class='genmed'>QUOTE (billrows @ Dec 16 2004, 08:53 PM)</td></tr><tr><td class='quote'>Another question about the force curve. What is a good shape for a force curve? Mine has a big hump followed by a dip and then a short hump. Tks. </td></tr></table> My guess is that a dip in the middle suggests that you are engaging your back "late", and that leads to the short hump at the end by swinging with your back and pulling with your hands. I am not a coach or a particularly good erger, but I would think that is a bad thing. I remember posts about when to engage the back on the forum in the past, and whole articles studying the question, etc, and some debate about whether you should engage your back early in the drive or do more of the classical 3 phases: legs, back, arms. So there may not be one right answer on when to start with the back, even if there is agreement you shouldn't have that dip in your force profile. One of the things I noticed about rowing strapless is that I started engaging my back earlier in the stroke. You can't finish with a big back lean strapless, because then you fall off the back. I row with the force curve almost all the time, and it is clear that at least for me I get a left leaning haystack when I explode at the catch with my legs and engage my back early. If I get tired and/or lazy, I lose that profile and start getting bell curves or worst, dips, or gradual slope up to a hill.

[old] PaulS · Post by **[old] PaulS** » December 17th, 2004, 5:23 pm

Let's make sure that "engaging the back early", which is not incorrect, does not get interpretted as "opening the back early", which is incorrect. Many people, in an attempt to establish handle pressure quickly (a noble cause) will do so by taking the catch with either their back, arms, or both. While this can create a relatively quick rise in the force curve, that rise will be unsustainable and will lead to a caving in of of the back side of the stroke, since the body swing was used too early and the arms simply cannot support the load. The peak pressure will also not be as high, because as the back is opening the legs will not increase their force production to protect the back from injury. (Aren't our bodies wonderful?) From the catch, imagine a triangle formed from the seat to the handle to the shoulder, this triangle does not change shape for the first half of the leg drive. So while the back is "engaged early", meaning it must be in a strong position to support the load, the legs must be the muscles that catch the flywheel and load the handle first, allowing for a strong transition provided by the body swing, to a finish with the elbows being drawn back to bring the handle to the finish. And contrary to how it may seem, with a good finish, plenty of layback can be accomplished even without the straps.

[old] tomhz · Post by **[old] tomhz** » December 17th, 2004, 6:27 pm

</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td class='genmed'>QUOTE (PaulS @ Dec 17 2004, 09:23 PM)</td></tr><tr><td class='quote'> From the catch, imagine a triangle formed from the seat to the handle to the shoulder, this triangle does not change shape for the first half of the leg drive. So while the back is "engaged early", meaning it must be in a strong position to support the load, the legs must be the muscles that catch the flywheel and load the handle first, allowing for a strong transition provided by the body swing, to a finish with the elbows being drawn back to bring the handle to the finish.  </td></tr></table> I agree with you. I saw myself in video a few month ago and was very suprised how much my technique differed from this description: I was opening up too eary. Since then I am trying hard to improve this and I think it is paying off now. More load on the legs and somewhat faster drive and pace. Thinking about "pushing" the footplate away instead of "pulling the handle" helps in mastering this, I think. Do you have any more advice? Do you think this is equally important on the erg as on the water. I mean: has "opening up too early" the same negative effect on the results on the erg as on the water (there we go again.... ) Tom

[old] billrows · Post by **[old] billrows** » December 17th, 2004, 6:34 pm

My force curve is more like a suspension bridge;) . I believe it is from opening the back early, then running out of legs and back before the arms give the last little tug creating a second smaller spike. I found that the catch drill (legs only) makes a good higher and smoother curve, though not left leaning, and almost an equivalent split as a full stroke. I've got to find a way to fit the rest of the stroke in without losing the amplitude of the catch. Thanks for your great feedback! Bill

[old] michaelb · Post by **[old] michaelb** » December 17th, 2004, 7:01 pm

Thanks for the clarification. </div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td class='genmed'>QUOTE (PaulS @ Dec 17 2004, 04:23 PM)</td></tr><tr><td class='quote'>this triangle does not change shape for the first half of the leg drive. </td></tr></table> At least for me, changing the shape of the triangle half way through the leg drive was "early" since that seems contrary to legs first, then back, then arms. So the back motion overlaps with both the leg finish and the arm start. There is also more back movement than I originally used (I think in the materials I was given by C2 years ago when I bought my erg, they recommended minimizing back swing). So there probably are multiple causes of a dip in the middle of the force curve, but don't they all relate to back timing, positioning, and transitioning between the leg force and the arm force? Is it possible to cheat the force curve display? If you have a nice left leaning haystack most of the time does that indicate that you are least getting the basic timing and mechanics correct?

[old] PaulS · Post by **[old] PaulS** » December 17th, 2004, 10:33 pm

</div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td class='genmed'>QUOTE (bw1099 @ Dec 14 2004, 07:12 PM)</td></tr><tr><td class='quote'> I like to use the Force Curve display on the PM3. The y-axis is labeled "kg" and "lbs" and there are some tick marks. Does anyone know how many pounds or kg per tick mark? bw  </td></tr></table> I had a chance to make some live comparisons to a known scale and the PM3 hash marks. (While doing some ErgMonitor testing) It would appear that each hash mark represents 20kg, but the PM3 display is so small as to make that "my best guess", since there are so few pixels between hash marks to work with. Begin New Info: On very close inspection the first 5 hash marks are equal but the area above the 5th is 50% taller before it clips the top off and draws a solid horizontal line along the top edge. That would make the capacity of the Screen 130kg or 287lbs. The small blocks that make up the line are 3hx2w pixels, or roughly 5.65kg in height. There is about 10cm missing from the beginning of the stroke, but since the X axis is time, the undisplayed portion will vary due to flywheel speed. This is very close to 1 flywheel revolution, which would make some sense from a programming point of view. The X axis was very close to 1.2 seconds maximum, far to long to bother with, IMO. (0.9 sec would still be a very long time to be on the Drive for anyone with an interest in the Force curve) End New Info: Maybe when they update to have a stroke length option for the X axis the Y can be labelled. I'm sure one of the reasons they do not label it is to avoid the testosterone fest that will ensue with guys trying to "peg the display" and then beating their chests because of it. At least it would be something objective, unlike the "Max Pace for one stroke" silliness. Cheers!

[old] bw1099 · Post by **[old] bw1099** » December 19th, 2004, 12:02 am

<table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td class='genmed'>QUOTE </td></tr><tr><td class='quote'>I'm sure one of the reasons they do not label it is to avoid the testosterone fest that will ensue with guys trying to "peg the display" and then beating their chests because of it. </td></tr></table> I have tried to "peg the display" without success, although I came close. My typical stroke has a max that is about half way up.

[old] PaulS · Post by **[old] PaulS** » December 23rd, 2004, 11:20 am

See what I mean? I had a much closer look while doing further testing, and the results from that have been edited into my post above. Cheers!

[old] bw1099 · Post by **[old] bw1099** » December 24th, 2004, 12:16 am

After some rough calculations, I came up with about 16 kg per division. Fairly close to the 20kg you came up with. I assumed the shape of the force curve (including the part that gets cut off at the beginning) to be a sine wave, and took the x-axis to be distance. The area under the curve will be equal to the energy of the stroke, which can be calculated from watts and spm. In my experiment, I took some strokes until I got one that was 200 watts at 26 spm. That works out to 452 Joules per stroke. Distance I pulled the chain was 1.3 meters. Calculated maximum force was 546 Newtons = 55.7kg. On the monitor, maximum force was about 3.5 divisions, so a division = 15.9 kg = 35 lbs. bw

[old] PaulS · Post by **[old] PaulS** » December 24th, 2004, 10:59 am

That's a creative solution, however the X axis is known to be time, so would introduce some error into your calculation. You may find some information at this location useful: <a href='http://www.atkinsopht.com/row/peakpull.htm' target='_blank'>http://www.atkinsopht.com/row/peakpull.htm</a>

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