Concept2 Scaling to OTW

[jliddil]

Scaling concept II rowing ergometer performance for differences in body mass to better reflect rowing in water
A. M. Nevill 1 , C. Beech 1 , R. L. Holder 2 , M. Wyon 1
1 School of Sport, Performing Arts and Leisure, University of Wolverhampton, Walsall, West Midlands, UK , 2 Department of Primary Care and General Practice, The University of Birmingham, Birmingham, West Midlands, UK
Corresponding author: Alan M. Nevill, School of Sport, Performing Arts and Leisure, University of Wolverhampton, Gorway Road, Walsall WS1 3BD, UK. Tel: +44 1902 32 28 38, Fax: +44 1902 32 28 98, E-mail: a.m.nevill@wlv.ac.uk
Copyright © 2010 John Wiley & Sons A/S
KEYWORDS
body mass • power-to-mass ratio • allometric models • single-scull rowing performance • drag effect
ABSTRACT

We investigated whether the concept II indoor rowing ergometer accurately reflects rowing on water. Forty-nine junior elite male rowers from a Great Britain training camp completed a 2000 m concept II model C indoor rowing ergometer test and a water-based 2000 m single-scull rowing test. Rowing speed in water (3.66 m/s) was significantly slower than laboratory-based rowing performance (4.96 m/s). The relationship between the two rowing performances was found to be R2=28.9% (r=0.538). We identified that body mass (m) made a positive contribution to concept II rowing ergometer performance (r=0.68, P<0.001) but only a small, non-significant contribution to single-scull water rowing performance (r=0.039, P=0.79). The contribution that m made to single-scull rowing in addition to ergometer rowing speed (using allometric modeling) was found to be negative (P<0.001), confirming that m has a significant drag effect on water rowing speed. The optimal allometric model to predict single-scull rowing speed was the ratio (ergometer speed ×m−0.23)1.87 that increased R2 from 28.2% to 59.2%. Simply by dividing the concept II rowing ergometer speed by body mass (m0.23), the resulting "power-to-weight" ratio (ergometer speed ×m−0.23) improves the ability of the concept II rowing performance to reflect rowing on water.

[Carl Watts]

Thought this had already been covered with the C2 online calculator ?

http://www.concept2.com/us/interactive/ ... stment.asp

At he end of the day I wouldn't try and directly compare the two of them anyway. You actually need better technique OTW and it has been pointed out the C2 Erg is just about producing power or Watts at the end of the day and anything goes as far as technique is concerned as long as your putting out the power. The Erg is a rowing "Simulator" and an excellent tool for directly comparing one rower to another using all of the information available from the Performance Monitor.

[ThatMoos3Guy]

Anyone with a calculator want to check what kind of results this formula gets compared to the C2 formula? I'd do it myself, but my calculator's broken and I don't understand exel.

There's a link to the article here: http://www3.interscience.wiley.com/jour ... 1&SRETRY=0

Should note that the .23 and 1.87 are exponents, but they probably didn't copy over well.

[Citroen]

There's a link to the article here: http://www3.interscience.wiley.com/jour ... 1&SRETRY=0

That link gets 404'd due to a missing browser cookie. Probably needs a subscription and login or something like that for it to work.

[NavigationHazard]

http://www3.interscience.wiley.com/jour ... 3/abstract

should get you the abstract. You need a log-in/subscription to see the whole article.

IIRC the C2 weight adjustment calculator adjusts erg times for a hypothetical eight. If that's true, direct comparisons with a 1x adjustor will have only limited value. Also IIRC RowPerfect allows you to adjust on the monitor for weight/boat type. Maybe Roland can run some comparative 1x numbers if he's lurking and reads this.

FWIW I make the average erg score of the juniors in the study to have been 6:43.2, and the average 2k OTW result to have been 9:06.4. That rather large dry/wet gap suggests to me that the participants weren't particularly skilled scullers. I'd have to read the full study (and I'm off campus), but I wonder how they dealt with the issue of technical proficiency. Offhand I would expect the bigger juniors to have been steered into predominatly sweep rowing, thus less familiar with the demands of a 1x and for that reason relatively slower in such boats than their smaller, more accustomed peers.

[Nosmo]

IIRC the C2 weight adjustment calculator adjusts erg times for a hypothetical eight.

I was under the impression that the adjustment was just a basic scaling law and had nothing to do with the type of boat (except to make the final numbers more realistic).
Reasoning is that aerobic power is determined mostly by the ability to deliver oxygen which is proportional to the cross sectional area of the muscles (really the blood vessels) whereas mass is proportional to volume. So any increase in mass should increase the aerobic power by a 2/3 exponent. Since speed is proportional to the cube root of power, the relationship becomes speed is proportional to weight to the 2/9th power.
Of course everything else is never equal but that is the logic.

What this leaves out is that anaerobic power which is much small but still significant in a 2K is proportional to the muscle mass not cross sectional area. The formula should work better the longer the event. I don't think it works nearly as well for for 500m as it would for events over 5K (but i've never checked)

Now in a boat the skin friction on the boat is about 80% of drag. And that should also be proportional to weight to the 2/3 power. So to first order weight should not make any difference in a boat. To second order, one needs to add the weight of the boat in to the formula, which would give larger people an advantage since the boat weight is a smaller proportion of the total. A third order correction would need to take into account the proportion of effort that is anerobic and hence proportional to mass again giving heavier rowers the advantage. Fourth and fifth and sixth order corrections would have to account for effects of height, other components of drag, and the fact that depending on boat design the wetted surface area is usually not strictly proportional to weight to the 2/3rds power.

[NavigationHazard]

Your weight-adjusted score will be a pretty good estimate of your potential speed in an eight. If all eight rowers have the same adjusted score, then that eight should be capable of rowing that speed for a 2k race on the water—given perfect conditions and near perfect rowing effectiveness (nobody rows perfectly).

From the Weight Adjustment Calculator FAQs.

[Byron Drachman]

According to the physics of rowing website

http://www.atm.ox.ac.uk/rowing/physics/

there would be about an eight percent change in speed for each change in boat class. So there would be about a 26 percent change going from an eight with eight identical rowers to a single. So you could first use the weight adjustment calculator to estimate your speed in an eight, and then multiply your speed by 0.78 to estimate your speed in a single, using of course the usual assumption that technique is ignored.

[Nosmo]

Your weight-adjusted score will be a pretty good estimate of your potential speed in an eight. If all eight rowers have the same adjusted score, then that eight should be capable of rowing that speed for a 2k race on the water—given perfect conditions and near perfect rowing effectiveness (nobody rows perfectly).

From the Weight Adjustment Calculator FAQs.

OK, but this just refers to the scaling factor in front of the equation to make the numbers more realistic. Doesn't change anything that followed.

[NavigationHazard]

What about the cox that has to be hauled around in an viii, and not in a 1x? Or are you counting that as part of deadweight in a second-order correction?

I'm not defending the C2 formula (and I have no idea what it actually is), mind you....

EDIT: apparently it's wf=[body weight in pounds/270] ^ .222

So for a 220lb rower with a 6:00 erg score wf is (220/270)^.222 = .956; multiply 360 seconds by .956 and you get the 5:44 time returned by the calculator.

[Bob S.]

What about the cox that has to be hauled around in an viii, and not in a 1x? Or are you counting that as part of deadweight in a second-order correction?

I'm not defending the C2 formula (and I have no idea what it actually is), mind you....

It is interesting to compare boat times: x>->+ - also 8+ just barely > 4x and 4+ just barely > 2x. I haven't seen enough 2+ scores to compare with 1x. The x>- suggests to me that the symmetry of sculling is more efficient than the alternate spacing of sweep oars.

Incidentally, my own favorite is the 1-, with the lock mounted on the transom. In some regions it is done with a hole in the transom. I have done it and seen it done only in a standing position, but I suppose that it could be done with a sliding seat that is mounted crosswise. Actually the movement of the blade in the water is too short to require that much body movement. It is all a matter of moving arms and shoulders and keeping feet well braced. I have never tried a 1+. It would have to be a bow cox, because the oar would be slamming into anyone on the stern thwart. Also, no one builds sculling (in the one oar sense) boats with rudders, since the single oar is used for steering as well as propulsion.

http://councill.home.mindspring.com/sbj ... cull1.html

Bob S.

Edit: I see that on that website, the boat illustrated doesn't even have a transom since it is a double-ender; the lock is mounted on the gunwale where it starts to curve in toward the pointed stern.

[Byron Drachman]

What about the cox that has to be hauled around in an viii, and not in a 1x? Or are you counting that as part of deadweight in a second-order correction?

I'm not defending the C2 formula (and I have no idea what it actually is), mind you....

EDIT: apparently it's wf=[body weight in pounds/270] ^ .222

So for a 220lb rower with a 6:00 erg score wf is (220/270)^.222 = .956; multiply 360 seconds by .956 and you get the 5:44 time returned by the calculator.

Yep. See formula 4.4 here:

http://www.atm.ox.ac.uk/rowing/physics/ ... l#section2

[Nosmo]

also see:
http://biorow.com/RBN_en_2007_files/200 ... News07.pdf
http://biorow.com/RBN_en_2007_files/App ... News08.pdf
and http://biorow.com/RBN_en_2007_files/200 ... News08.pdf


Nav, yes one would have to take into account the coxwains, oars, clothing etc. All of the additional corrections are just theoretical. The 2/3 power exponent (or 2/9 =.222 speed exponent) I believe is derived as I indicated. But I wouldn't take any of this too seriously. The basic formula is a good fitness comparison for rowers of different weights. As you well know one must be able to move the boat (and to fit in with the others for bigger boats

[ErgCalc]

The Concept2 weight adjustment formula (which I also use in my ErgCalc calculator) is only to compare split times from people with varying weights.

I use it when comparing erg scores - the heavy girl may do better than the light girl split-time wise, but once you take their body weight differences into account, the picture typically changes a lot.

[lintonwilson]

Thought this had already been covered with the C2 online calculator ?

http://www.concept2.com/us/interactive/ ... stment.asp

At he end of the day I wouldn't try and directly compare the two of them anyway. You actually need better technique OTW and it has been pointed out the C2 Erg is just about producing power or Watts at the end of the day and anything goes as far as technique is concerned as long as your putting out the power. The Erg is a rowing "Simulator" and an excellent tool for directly comparing one rower to another using all of the information available from the Performance Monitor.

Carl,,,,From the look of your avatar there are two PM's connected to your erg.....Would you please explain....thanks