Re: Let's go Dynamic
- From: Carl Douglas <carl@xxxxxxxxxxxxxxxxx>
- Date: Thu, 20 Jan 2011 00:00:01 +0000
On 19/01/2011 21:34, Zbigniew A. wrote:
Two days later i made a series of timed 500m pieces.
My aim was to establish whether results of timed pieces made on three
different types of C2 ergs can be compared directly.
So i've put three machines side by side. After a long and thorough
warmup i made 12 x 500 m on fixed, dynamic and on slides, 4 rounds. I
tried to keep the same *subjective* level of intensity, about my 2k
pace. I tried not to look at the display readings, i would only look up
my HR, if anything. After each 500m trial there was 2 minutes AR and one
minute for a change -- start every 5 minutes. All results were stored on
a memory card and analyzed later at home.
All 12 trials returned *very* *similar* results: almost the same times
and the same heart rates, with one parameter varying consistently -- the
My average cadence on fixed head was 30,5, on dynamic 27,5 and on slides
Frankly, I find it counter intuitive and don't know what to make of it.
My coach has the complete spreadsheet with these results, maybe he will
find out. That was made a week ago and I moved on already.
What Cas Rekers did when validating Rowperfect was to work with an academic in Berlin (Justus may recall the name, I think it was something like Schwann, but that could be quite wrong). They inserted a dynamometer setup in the chain - i.e. a measuring device able to generate an absolute measure & record of instantaneous force & speed throughout the stroke.
With the data from this equipment, they compared input power with the monitor record on the RP, and found this correlated very well throughout the power range. They also measured power vs heart rate & rating, both with the RP working in its normal dynamic (sliding head) mode & then with the head movement locked (in which condition it had the same non-dynamic characteristics as the fixed C-II machine). Again the monitored & dynamometer readings correlated well.
However, a substantial & consistent difference in the delivered (i.e. monitored) power was measured between the 2 modes with the subject rowing at the same heart rate. There was a deficit in both monitored & dynamometer computed power in the fixed head setup, amounting (from memory) to ~130 watts. This deficit appeared to represent the extra work required by the rower in simply accelerating & decelerating his body, first up, & then down, the slide every stroke before actually doing any work on the handle.
You may agree with me that none of that sounds counter-intuitive?
They also found that the monitor readings on a C-II machine (the model C IIRC), which they also fitted with the same dynamometer arrangement, were themselves less accurate. Not just that, but the power monitored varied markedly according to the force profile employed.
This last - the variability - I attribute to the far from ideal intake geometry of that machine (seen as a piece of turbomachinery) & the use of a pleasantly quiet fan of a design which is bound, as most well-designed fans are, to be peaky in its performance, whereas the early C-II machines & the RP had fans which, by simply beating up the air that passed through them) generated the required Drag = k V^2 relationship pretty well.
Anyone wanting to row faster (or to coach others to do so) must be ready to create meaningful test scenarios & rigorously evaluate them. This is not to hard to do, but if the conclusions depend to any extent on rower perception then we risk getting them wrong. I'm not saying you got it wrong, but you said your results were counter-intuitive. I feel that a flaw in your test protocol was the lack of an absolute measure of performance - which only a dynamometer could provide.
What do you think?
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Email: carl@xxxxxxxxxxxxxxxxx Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
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