Static vs. Dynamic ERG Split Differences

[LA329]

Hi All -- while this may have been covered in the archives, the Concept 2 folks suggested I post. I own a Dynamic since I am an avid competitive rower and it has really helped me work on some of the finer points of increasing boat speed on the water.

That said, I enjoy competing in (Static) Erg Events from time to time, and I am looking for empirical (or just plain perspective informed by experience) regarding whether one would expect a rower AT THE SAME STROKE RATE to be faster or slower on a Static vs. a Dynamic at 1K, 2K and 5K?

Thanks a lot ... just don't want to be surprised at my next ERG event that I show up to and finding that my splits are not what I would have expected based on my training on the Dynamic.

[jamesg]

Extra inertial Power losses on the static erg have been estimated at 10-20%:
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... #section12

The Dynamic also allows a quicker and so shorter catch than the Static, due to smaller masses to be accelerated and so higher acceleration before the catch, at the same force. This suggests another possible estimate, based on stroke length:

If the length difference is 10cm, average handle force 40kg and rating 30, the loss of power delivered on the static machine would be: 0.1 x 40g x 30/60 = 20W.

[Carl Watts]

Would expect some pretty significant improvements in times on the Dynamic especially if your taller and heavier.

There are some big differences even for a static erg on slides. Some fast rowers on RowPro that it turns out are on slides. Some moved to the slides due to back issues which would suggest there is a possibility they couldn't even come close on a static or even possibly not be able to row on a static at all..

[hjs]

Hi All -- while this may have been covered in the archives, the Concept 2 folks suggested I post. I own a Dynamic since I am an avid competitive rower and it has really helped me work on some of the finer points of increasing boat speed on the water.

That said, I enjoy competing in (Static) Erg Events from time to time, and I am looking for empirical (or just plain perspective informed by experience) regarding whether one would expect a rower AT THE SAME STROKE RATE to be faster or slower on a Static vs. a Dynamic at 1K, 2K and 5K?

Thanks a lot ... just don't want to be surprised at my next ERG event that I show up to and finding that my splits are not what I would have expected based on my training on the Dynamic.

Think you best simply try out a static erg.

Rating, the biggest difference is rating, static is lower, you need to move your body. You won,t be able to use rates you get on the Dynamic. Or rates you get otw.

[Remo]

That said, I enjoy competing in (Static) Erg Events from time to time, and I am looking for empirical (or just plain perspective informed by experience) regarding whether one would expect a rower AT THE SAME STROKE RATE to be faster or slower on a Static vs. a Dynamic at 1K, 2K and 5K?

Extra inertial Power losses on the static erg have been estimated at 10-20%:
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... #section12

The Dynamic also allows a quicker and so shorter catch than the Static, due to smaller masses to be accelerated and so higher acceleration before the catch, at the same force. This suggests another possible estimate, based on stroke length:

If the length difference is 10cm, average handle force 40kg and rating 30, the loss of power delivered on the static machine would be: 0.1 x 40g x 30/60 = 20W.

Careful James, there is a lot of bad physics in the source you cite. The basic premise of that article is that you have used more energy to accelerate your body than you would on a dynamic erg and that this extra energy is irredeemably lost. In fact, that energy is not lost.

Have you ever rowed or erged with your feet out of the stretchers? Great drill. So what stops you from flying off the back of the slides? It is not the stretchers. I've seen an oarsmen fly off the back when a cable broke on one of the old Gamut ergs. It looks like this clip, only worse because the oarsman has a bunch more kinetic energy than this poor guy: https://www.youtube.com/watch?v=1ezFwRun9_Q.

It is the oar handle that stops the rower. All of the rower's kinetic energy is transferred to either the water or the erg flywheel. The force the rower applies to the handle is equal and opposite to the force the handle applies to the rower and it is this counter force by the handle which arrests the rowers backward motion. Classic Newton's 3rd law.

That is not to say that there aren't some inefficiencies associated with rowing a static as opposed to a dynamic erg (the biggest one being at the front -- not the back -- end). But any such inefficiency is an order of magnitude less than suggested by the article.

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Now back to LA329's original question.

The static erg has a heavier front end and a lighter back end than the dynamic. It will also be heavier in general. (Think pair with). Your stroke rating will by necessity be lower and the force you apply to the handle will go up a bit

Your splits -- provided you are comfortable on both machines -- should be about the same. Because on both machines what is being measured is energy output, which is really just muscular and cardiovascular fitness. As an example, the fastest 10k ever rowed is 31:05.2 which was done by the great Eric Murray on a STATIC erg in 2015. This broke the record of 31:17.2 which Mr. Murray set in 2012 rowing on a DYNAMIC erg. https://www.concept2.com/indoor-rowers/ ... weight=Hwt

That said, you are not Eric Murray and you might not be able to easily go from one erg to another. Here is to you being adaptable and being able to row both machines well.

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[Tinpusher]

True it is easier to rate up on slides/dynamics when compared to a static erg, but in order to sustain it for 2k, 6k, 10k or more, requires the erger to be very fit.
Just saying that anyone can go faster on slides/dynamics than on a static because you can rate up is only partly correct. Most cannot sustain the higher rate due to fitness limitations and If using the same rate, there is very little difference between the equipment.
Technique on slides/dynamics is more important than on a static. Poor rowing technique is not a penalty on a static but will be on slides/dynamics.

[Ombrax]

Poor rowing technique is not a penalty on a static

David, I'm 99.99999% sure you really didn't mean to say this as written, because we all know that bad technique on a static erg can have a huge impact on someone's ability to row efficiently.

I assume you meant it isn't quite as important as on a dynamic erg, but it's still a big issue on a static.

[Tinpusher]

I've seen some truly horrible techniques on the erg (not the youtube comedy ones) and the score doesn't reflect how badly they are "rowing". They just overcome the technique with strength or fitness and could go faster with better technique. Try anything like that on slides/dynamics and the results will not be so kind.
So I did mean it to a point. Shooting the slide and other gross errors will be a penalty on any equipment, but anchor hauling may only be a penalty on slides/dynamics.

[jamesg]

So what stops you from flying off the back of the slides?

Pulling the handle, which is work done. On a Dynamic, body-mass speed is much lower, so there's less work to be done to stop, and more is transferred to the flywheel, if we hold the total constant.

[Remo]

So what stops you from flying off the back of the slides?

Pulling the handle, which is work done. On a Dynamic, body-mass speed is much lower, so there's less work to be done to stop, and more is transferred to the flywheel, if we hold the total constant.

I think that we are about on the same page. It is my thesis that all of the kinetic energy generated is transferred to the flywheel via the pulling of the handle. And further that apart from the pulling of the handle, there is no work done to stop with either the dynamic or static erg.

The reality is slightly different in that the foot straps -- unless you are rowing feet out -- will absorb some of the energy. You will have some loss at the front end where you slow the body coming into the catch (although not all of this energy is lost because muscles, when stretched, act like a spring and damper).

As an aside you also have the rotational energy of your limbs to deal with (which is similar in size as the energy used to accelerate the center of mass) and if the article was in fact correct would cause the alleged difference between a static erg and a dynamic erg to be much less

I'll be away for a few days, and if you wish to continue this conversation ponder this: If the energy generated by the body is not going to accelerating the flywheel, where is it going? What is the energy sink? What is getting hot? The excess energy has to go somewhere (conservation of energy).

[Nomath]

... I am looking for empirical (or just plain perspective informed by experience) regarding whether one would expect a rower AT THE SAME STROKE RATE to be faster or slower on a Static vs. a Dynamic at 1K, 2K and 5K?

I don’t have own empirical data, but I have read several papers in sport science journals that compare the two types of rowers.
From these I reckon that you will be slower on a dynamic erg on all distances, on the condition of same stroke rate.

The main reason, shown by these studies, is that for most of the drive cycle the force that you can apply on the handle is much lower (ca. 10%) for the dynamic erg. In order to keep the power at the same level, you have to increase the stroke rate by about the same percentage. So keeping the stroke rate the same will slow down the pace of the dynamic erg.

See the paper Comparison of rowing on a Concept2 stationary and dynamic ergometer, by Aaron Benson and coauthors (2011)
https://www.researchgate.net/publicatio ... _Ergometer

Extra inertial Power losses on the static erg have been estimated at 10-20%:
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... #section12

Yes, on a static erg the rower is required to put energy in accelerating the body in the slide. The extra inertial power is estimated at 10-20%, but the cited text does not explicitly say that this energy is lost! There is a good case to be made that the kinetic energy of the moving body build up in the first part of the drive phase is NOT lost. With good rowing technique, in the second part of the drive the body is slowed down and stopped by pulling on the erg handle. Hence the kinetic energy is used to power the flywheel. Otherwise the body had to be stopped by a pull on the foot straps. Specific measurements of forces on the footholds show that there is not such a pull.

A similar but less obvious argument can be made for the sliding energy in the recovery on a static erg. Measurements of the forces on the footholds and on the seat show that during the second part of the recovery the weight of the rowers body is gradually lifted from the seat and transferred to the legs. At the catch position, only about one-quarter of the body weighs on the seat and three-quarters rests as a vertical force on the footholds. The rowers center of mass is also slightly lifted. This squatted position is a way of storing the kinetic energy of the recovery : the muscles and tendons acting like springs. It allows the rower to launch his body in the first phase of the drive.

This is a picture resulting from a study that measured the horizontal and vertical forces on handle, foodholds and seat in a static and dynamic ergometer, titled Fixed versus free-floating stretcher mechanisms in rowing ergometers - Mechanical aspects, by F. Colloud and coauthors (2006).
http://bionics.seas.ucla.edu/education/ ... 006_02.pdf

[jamesg]

Since body-mass speed changes are smaller on the dyno or slides than on a static erg, there can be no doubt that less work is needed to cause those changes.

How that work can be recovered on a static, or used elsewhere on any type of dyno, depends on physics first and second on finding and using ways to do it.

I think it may be possible to go faster on a Dyno, for the same overall effort, maybe via stroke length. But any dfference cannot be large and it's not worth worrying about.

[hjs]

Since body-mass speed changes are smaller on the dyno or slides than on a static erg, there can be no doubt that less work is needed to cause those changes.

How that work can be recovered on a static, or used elsewhere on any type of dyno, depends on physics first and second on finding and using ways to do it.

I think it may be possible to go faster on a Dyno, for the same overall effort, maybe via stroke length. But any dfference cannot be large and it's not worth worrying about.

You see people rate a lot higher. Wr 6k for instance, 129.x at rate 37. Rating that high on a static erg seems very very tough.

[frankencrank]

That said, I enjoy competing in (Static) Erg Events from time to time, and I am looking for empirical (or just plain perspective informed by experience) regarding whether one would expect a rower AT THE SAME STROKE RATE to be faster or slower on a Static vs. a Dynamic at 1K, 2K and 5K?

Extra inertial Power losses on the static erg have been estimated at 10-20%:
http://eodg.atm.ox.ac.uk/user/dudhia/ro ... #section12

The Dynamic also allows a quicker and so shorter catch than the Static, due to smaller masses to be accelerated and so higher acceleration before the catch, at the same force. This suggests another possible estimate, based on stroke length:

If the length difference is 10cm, average handle force 40kg and rating 30, the loss of power delivered on the static machine would be: 0.1 x 40g x 30/60 = 20W.

Careful James, there is a lot of bad physics in the source you cite. The basic premise of that article is that you have used more energy to accelerate your body than you would on a dynamic erg and that this extra energy is irredeemably lost. In fact, that energy is not lost.

I agree. That paper compared the static erg with a shell on the water (which the dynamic erg is supposed to better replicate) I personally think his errors are such that there is little difference, energy wise, between a static erg and a shell on the water as opposed to his estimate of 35 watts. Not sure about a dynamic erg.

[jamesg]

The 30 W power loss Dudhia estimate was at rating 30 and with 1m/s cg peak speed, if I remember right; don't remember the weight.

These estimates always approximate real conditions, since we don't know mass, ratings, speed ratio, where the cg is and how fast it travels.

However, to some approximation, rowing is done by 80kg oarmen with the pull at roughly 2m/s (ergdata) so maybe 1m/s (cg). At high ratings the recovery will be at similar speed to the pull, but at low the recovery speed is less and recovery ke can be ignored.

So the ke in the pull is 80 x 1²/2 = 40Nm.
At rating 20 this is 20*40/60 = 13W. At rates 30-35, maybe 2-3 time higher.

This potential loss if we want it to somehow appear in the flywheel, we have to put it there; with a longer harder or faster stroke. At least, the dyno makes it easy to pull longer strokes at higher ratings, so we'll probably need to avoid overdoing it.


As for ke being recoverable on a static erg, this is over optimistic where muscle is involved. To stop at either end, we contract muscle, and this is not free of charge. Our MTUs are not made of rubber, they are designed to do work, not store it. Any "missing" work or energy will turn up as heat.

Recovering kinetic energy can only happen when the energy is stored somewhere, as potential energy (height) or as elastic energy as in a spring or a bouncing ball. Elastic recovery is used in gangsaws, where to reduce load on the flywheel system some machine builders fit cushions at both ends of frame travel. Such frames may weigh 10-20 tons and travel fast, so it's well worth doing.
https://www.youtube.com/watch?v=HXa3Gdz1OPk