Effects of the drag factor on performance and on physiological parameters

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jamesg
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Re: Effects of the drag factor on performance and on physiological parameters

Post by jamesg » November 23rd, 2020, 6:17 am

To investigate the erg as a tool for measuring whole-body peak power and finding the best drag factor for that.
But they conclude that it doesn't work:
When unskilled individuals use this test, 1 familiarization session before the actual measurement is recommended.
Finally, practitioners should be aware that power output values displayed on the Concept II rowing ergometer markedly underestimate true power output generated by the individual.

So back to square 1: what's the purpose of a peak test? There's no point in trying to foresee how it should be set up if we don't know what it's for.

One purpose could be to identify potential, numerically, not wanting to send beginners afloat who might not come back alive. Put them on the erg and tell them to do the best or worst they can, even with no technique or training; there's a limited number of seats in boats.

But anyone can pull a few long hard strokes when there's no need to rush at it, and the machine can give us a number that does not suffer a relationship to rating. By all means set the drag high if you think it can help find what you're looking for. Training and technique come later.
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Re: Effects of the drag factor on performance and on physiological parameters

Post by Nomath » November 23rd, 2020, 5:42 pm

jamesg wrote:
November 23rd, 2020, 6:17 am
So back to square 1: what's the purpose of a peak test? There's no point in trying to foresee how it should be set up if we don't know what it's for.
The purpose of the Zagreb study was to assess whether the Concept2 erg is suitable to measure anaerobic peak power. In physiology there are two kinds of peak power: anaerobic and aerobic. Maximal aerobic and anaerobic power are crucial determinants in many sport disciplines. Aerobic power matters e.g. in long-distance running, cycling and rowing. Anaerobic power matters in 'explosive' activities, like sprinting, jumping and throwing disciplines in athletics, sprints in cycling, short distance speed skating, kayaking, volleyball and basketball, etc.

Aerobic peak power is usually measured by exercising on an erg with a power ramp or power steps until exhaustion. It takes roughly 10-15 mins.

For measuring anaerobic peak power, a widely used test is the countermovement jump : standing on a platform, bend the knees until about 90 degrees angle and jump up with maximal leg force. From the height of the body centre mass or the time-of-flight, the specific peak power (W/kg) can be determined. Some male elite athletes have reached 50-65 W/kg in this test, which at, say 65 kg, amounts to 3500W. A disadvantage is that for an accurate measurement a force-logging platform is needed, which is only available in sport labs. Peak power test have also been done on cycle ergs. Elite cyclists reached 20-23 W/kg when assessed over 1 sec. This shows how dependent the peak power is on the measurement tool and the duration of the effort.

The Zagreb study investigated whether a C2 rowing erg is a suitable tool to measure anaerobic peak power because C2 ergs are widely available in gyms and at home and have an in-built power measurement. Additionally, it would involve a lot more muscle groups than just the legs.

I agree that the result of the study is that it doesn't work. The main reason is that the rowing stroke is too complex for non-rowers. They are at a strong disadvantage to experienced rowers. One familiarization session or even a couple of days is not enough to close the 50% gap in peak power between the 'active' group and the group of experienced club rowers.
The second issue is whether the C2 accurately measures true peak power. I cannot believe that the C2 measurement is a factor of 3 wrong, as the Zagreb study observed, but the C2 accuracy is certainly worth further investigation. The way the flywheel angular speed is processed by the C2 performance monitor is proprietary and has not been disclosed. Validation by independent parties is desirable.

The reason I mentioned the Zagreb study in this topic is that they used 3 drag factors, ranging from 90 to 200. Interestiingly, for experienced rowers the drag factor setting did not significanly affect the peak power result.

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Re: Effects of the drag factor on performance and on physiological parameters

Post by jamesg » November 24th, 2020, 11:27 am

I cannot believe that the C2 measurement is a factor of 3 wrong
Me neither, and in fact it's not, the PM measures work done by the fan and then calculates power using the complete stroke time, so 2 seconds at rating 30, 3s at 20. This is what's needed to estimate boatspeed (W=kV³) and so pace.

But the Croats say they measured what they wanted, peak power directly at the handle, so no averaging: speed x force. This is enough to explain the factor 3, which in any case will depend on the rating used in the tests: the pull takes about 0.65s, so at ratings around 30, factor 3 is to be expected.

On a standard PM with ergdata, peak power data or close can be derived from pull speed and average or peak forces. Typically in slow work at 20 I see 35kg average and 1.8m/s, which implies 35xgx1.8 = 630W, while PM says 120-130W.

As for accuracy, the PM relies on the intermittent rowing action to observe flywheel speeds via the impulse stream, at each finish and at the start of the next stroke. This is enough to calculate the overall work done by the fan, just after the stroke ends. Accuracy will depend on clock resolution. Important is that it be consistent and not subject to drift, temperature, false zero etc, so need no calibration, as could be with strain gauges.
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Re: Effects of the drag factor on performance and on physiological parameters

Post by Nomath » November 24th, 2020, 5:44 pm

So you speculate that they took not only the most powerfull stroke out of 6, but also the singular moment in that stroke with the highest power output. You may be right or you may be wrong. Here is what the authors explained what they did :
The highest external power output yielded during these "all-out" strokes (in watts per kilogram) at each resistance setting was recorded as the peak setting. A similar procedure for peak output power assessment on the Concept II rowing ergometer was also applied by Gee et al. (6) and Ingham at al. (10).
Reading this I first looked at what Gee and Ingham did (full details in the References section in the paper). They didn't use a force and displacement sensor on the handle, so they didn't have a power profile of each stroke. Your speculation seems at odd with the above.
I can imagine 4 different options more or less matching the above text :
(1) the average power of 6 consecutive maximal strokes. This is what Gee en Ingham used (Gee did 5 strokes).
(2) the most powerful of the 6 strokes.
(3) the most powerful of the 6 strokes discounting the time of the recovery of that stroke.
(4) the most powerful moment in all of these 6 strokes.
You speculate on (4). I speculated on (3), which would explain roughly a factor of 2.
Last week I mailed the corresponding author of the paper, Prof. Goran Markovic. He replied that unfortunately this was mostly a Ph.D study of the first author with whom he lost contact. Also the C2 erg equipped with force and displacement sensors was no longer available. So the issue remains unresolved.

Does it matter? Probably not for the vast majority of C2 erg users. They require consistency. However, it does matter for elite rowers who want to experiment with different power profiles and wonder whether the C2 performance monitor gives an accurate account of the variations. Or for erg freaks who experiment with the drag factor and find that what they 'feel' is different from what the PM displays.
There have been earlier investigations of the C2 power measurement (e.g. Boyas, Int.J.Sports Medicine,2006 ), which cast doubt on the C2 accuracy. Not only an understandable systematic difference of some 25W, probably caused by losses in the chain drive, but also much larger discrepancies during the start or strong stroke-to-stroke variations. In fact, anybody sitting on a C2 erg can check that if you row alternatingly with a strong and a weak stroke, you are surprised at what you see displayed on the PM.
The main calibration problem is that a human rower is not very accurate in reproducing strokes. Fortunately, a calibration and validation study with a motorized driver is underway.

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Re: Effects of the drag factor on performance and on physiological parameters

Post by jamesg » November 25th, 2020, 2:56 am

A simple interval test (say 20x100m) can be used to get enough data to investigate the effects of drag in a C2. I found small differences in power from 90 to 200, and larger differences in work. How the work is done in terms of force/speed varies considerably.

It's well known and seen every day that the C2 measurement system can show odd results when data is incomplete as at starts. This is easily avoided once understood how it works.

Why do you think the C2 needs calibration? What would you use as a reference?
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Re: Effects of the drag factor on performance and on physiological parameters

Post by Nomath » November 25th, 2020, 2:52 pm

jamesg wrote:
November 25th, 2020, 2:56 am
Why do you think the C2 needs calibration? What would you use as a reference?
Why? I think I answered this in the above after 'Does it matter?'

How? Calibration and validation is a professional branch of technology, see Wikipedia. You should use measuring tools that are traceable to primary standards. A force sensor and a displacement sensor seem to me tools that can be calibrated very well. They should have good dynamic accuracy. Regarding the proper force-speed profile, C2 claims that it is self-calibrating so any test profile is OK. If discrepancies are found, this is more relevant if the profile is human-like. Reading the paper from Ulm University that I cited, I trust that they know what they do (e.g. J.M. Steinacker is an authority in rowing and in biomechanics).

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Re: Effects of the drag factor on performance and on physiological parameters

Post by Nomath » November 28th, 2020, 1:40 pm

A worthwhile addition to the issue of peak power measurement and to the issue of accuracy of the C2 power measurement :

To summarize these issues: a paper from Zagreb University found for a group of young experienced rowers (men and women) an average peak power of 23.5 W/kg for 6 "all-out" strokes and stated that the power displayed by the C2 performance monitor underestimates the true peak power by a factor of ~3.

I found another paper, published in 2007, that measured more or less the same peak power with different tools. It is from the Kinesiology department at the University of Texas in Austin. The tool was a modified C2 erg. The main modification was that the flywheel with fan vanes was replaced by a more heavy, solid brass disc with 15 slots. These cleverly spaced slots enabled to measure the rotation speed of the flywheel by an optical sensor. Because of the much higher sampling rate per rotation (C2 uses 3 magnets and a Hall sensor) and because the rotation speed data were not processed in real time, the accuracy of the Austin power measurement is likely much better and more detailed than from the C2 system. The high sampling rate enabled them to measure instantaneous power accurately.

The participants were young male varsity rowers (more details in the paper). After a 3 min warm up on a conventional C2 rower, each participant moved to the modified rower and performed five trials consisting of 6 maximum-intensity strokes. Between the trials there was 3 min of low intensity rowing. To help the rowers, the seat had a high friction surface and a seat belt. The ergometer was bolted to the floor.
The figure below is taken from the paper and shows the instantaneous power during the 6 strokes from a representative trial.

Image

Because the first stroke starts with a standstill flywheel, it is much slower than the next and power is also lower. The authors distinghuished between maximum stroke power, maximum pull power and maximum instantaneous power. Maximum stroke power is work during the drive phase divided by the time of drive + recovery phase, which is the same as the way C2 calculates power. The maximum pull power is work divided by the duration of the drive phase only. Maximum instantaneous power is the highest peak value in the 6-stroke sequence.

The average maximum stroke power for these 11 well-trained athletes was 812 W or 9.8 W/kg. The maximum pull power was 1995 W or 23.9 W/kg. The last number is very close to the Zagreb study (23.5 W/kg), which makes it very likely that the Zagreb study also calculated the power for a single stroke and discounted the time of the recovery. The average maximum instantaneous power was 3489 W or 41.9 W/kg. This is already close to instant peak power measured in elite countermovement jumps (CMJ), 50-65 W/kg.

Knowing this, it is not difficult to calculate the underestimation of pull power by the C2 performance monitor using data from RowErg. The RowErg shows stroke rate, drive length and drive speed. From stroke rate, the stroke time can be calculated: Ts=60/sr. From drive length and drive speed, drive time can be calculated: Td=Ld/Vd. Pull power relates to stroke power by a factor Ts/Td.

The main objective of the Austin study was to measure force-velocity relationships on a C2 erg. Because a solid brass disc is much less decelarating from air friction during the recovery, participants have to pull over a wider range of velocities. The figure below shows the relationship for the pull phase (solid squares). This graph helps to better understand what a change in the drag factor does. With a higher drag factor, the rotation speed of the flywheel drops faster during the recovery. Hence, after the catch the handle speed matches the speed of the flywheel earlier in the drive, but due to the lower speed we can pull with a higher force. Conversely at a lower drag factor, for the same acceleration of our body it takes longer to catch up with the flywheel but our higher body speed (=handle speed) does compensate the lower pull force. It is not only likely that the optimal drag factor depends on body weight but also on agility. My guess is that seniors benefit from using a higher drag factor than adviced in the tables.

Image

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Re: Effects of the drag factor on performance and on physiological parameters

Post by mict450 » November 29th, 2020, 2:27 am

Nomath wrote:
November 28th, 2020, 1:40 pm

It is not only likely that the optimal drag factor depends on body weight but also on agility. My guess is that seniors benefit from using a higher drag factor than adviced in the tables.
This "guess" seems to support my earlier conclusion of experimenting with increasing drag.
My vital stats: 66 y/o, 5' 5", 130 lbs; current damper @ 3, DF 75, alt: 3200 ft. Musing on gradually increasing to 90-95 for UT2 work. Sensible??
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Re: Effects of the drag factor on performance and on physiological parameters

Post by hjs » November 29th, 2020, 5:50 am

mict450 wrote:
November 29th, 2020, 2:27 am
Nomath wrote:
November 28th, 2020, 1:40 pm

It is not only likely that the optimal drag factor depends on body weight but also on agility. My guess is that seniors benefit from using a higher drag factor than adviced in the tables.
This "guess" seems to support my earlier conclusion of experimenting with increasing drag.
My vital stats: 66 y/o, 5' 5", 130 lbs; current damper @ 3, DF 75, alt: 3200 ft. Musing on gradually increasing to 90-95 for UT2 work. Sensible??
75 is super low, not saying its wrong, but way below what is considered normal.

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Re: Effects of the drag factor on performance and on physiological parameters

Post by mict450 » November 29th, 2020, 6:42 am

hjs wrote:
November 29th, 2020, 5:50 am
mict450 wrote:
November 29th, 2020, 2:27 am
Nomath wrote:
November 28th, 2020, 1:40 pm

It is not only likely that the optimal drag factor depends on body weight but also on agility. My guess is that seniors benefit from using a higher drag factor than adviced in the tables.
This "guess" seems to support my earlier conclusion of experimenting with increasing drag.
My vital stats: 66 y/o, 5' 5", 130 lbs; current damper @ 3, DF 75, alt: 3200 ft. Musing on gradually increasing to 90-95 for UT2 work. Sensible??
75 is super low, not saying its wrong, but way below what is considered normal.
Back story: my close to 4 months experiment to teach myself to be fast & powerful on the leg drive per the Peter D video:

https://m.youtube.com/watch?v=hiQ0Mqlk_Lo

75 feels pretty normal now, but mebbe it's time to raise it back up.
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Re: Effects of the drag factor on performance and on physiological parameters

Post by hjs » November 29th, 2020, 7:51 am

mict450 wrote:
November 29th, 2020, 6:42 am
hjs wrote:
November 29th, 2020, 5:50 am
mict450 wrote:
November 29th, 2020, 2:27 am


This "guess" seems to support my earlier conclusion of experimenting with increasing drag.
My vital stats: 66 y/o, 5' 5", 130 lbs; current damper @ 3, DF 75, alt: 3200 ft. Musing on gradually increasing to 90-95 for UT2 work. Sensible??
75 is super low, not saying its wrong, but way below what is considered normal.
Back story: my close to 4 months experiment to teach myself to be fast & powerful on the leg drive per the Peter D video:

https://m.youtube.com/watch?v=hiQ0Mqlk_Lo

75 feels pretty normal now, but mebbe it's time to raise it back up.
If thats the reason, I would keep this (partly) in your scedule. Or else it will be lost soon.
I personally always liked low drag use, it gives a very fluffy stroke, fan keeps spinning, not much force needed to keep going.

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Re: Effects of the drag factor on performance and on physiological parameters

Post by frankencrank » December 13th, 2020, 5:33 pm

This is all pretty easy to explain from a physiological basis. It is the basis of my "experiment" in which I expect to show this phenomenon. Further, I would expect to see even further improvement at even higher drag factors in most experienced rowers, especially after a period of adaption.

The explanation? At any given power a muscle will have a most efficient contractile speed. Most cyclists (and rowers) foot speed is above the most efficient muscle contractile speed for the power they are at. Increasing the drag factor will slow the foot speed and increase efficiency. Resulting in either more power or a lower heart rate or both. With adaptation one could expect further increases.

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Re: Effects of the drag factor on performance and on physiological parameters

Post by mict450 » December 13th, 2020, 6:51 pm

frankencrank wrote:
December 13th, 2020, 5:33 pm

At any given power a muscle will have a most efficient contractile speed. Most cyclists (and rowers) foot speed is above the most efficient muscle contractile speed for the power they are at. Increasing the drag factor will slow the foot speed and increase efficiency. Resulting in either more power or a lower heart rate or both. With adaptation one could expect further increases.
Intriguing. Appears to give slight increase in performance to inactive & active rowers, less so to the club, elite rowers.
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Re: Effects of the drag factor on performance and on physiological parameters

Post by frankencrank » December 13th, 2020, 7:39 pm

mict450 wrote:
December 13th, 2020, 6:51 pm
frankencrank wrote:
December 13th, 2020, 5:33 pm

At any given power a muscle will have a most efficient contractile speed. Most cyclists (and rowers) foot speed is above the most efficient muscle contractile speed for the power they are at. Increasing the drag factor will slow the foot speed and increase efficiency. Resulting in either more power or a lower heart rate or both. With adaptation one could expect further increases.
Intriguing. Appears to give slight increase in performance to inactive & active rowers, less so to the club, elite rowers.
Remember, those studies gave no adaptation time. People tend to test best at what they are used to. To test best as something you are not used to says something. Pedal speed is the only cycling metric that correlates with efficiency. Pedal speed reflects muscle contraction speed. My work with cyclists suggests optimum pedal speed for about 200 watts is in in the 1.1m/s range. Most are in the 1.6-1.7 range. This is a typical age grouper. Most pros putting out 350 watts should be in the 1.4 m/s range. Most, again, are in the 1.6-1.7 range (the age-groupers copy what the pros do). I am not sure the translation to rowers is exact but I would be surprised if an elite rower were optimized at a slide speed much above 1.75 m/sec. The only way to know what is best for you is to test. Then change so it becomes normal to you then test again. The only problem I see is the Concept2 may not be able to get to the drag needed for many elites.

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Re: Effects of the drag factor on performance and on physiological parameters

Post by frankencrank » December 14th, 2020, 1:55 pm

Nomath wrote:
November 21st, 2020, 1:28 pm
Roaming through a lot of scientific studies on ergometer rowing, I hit upon a paper from a Kinesiology group at Zagreb University, published in 2015, in which the drag factor was deliberately set at the lower end (90), in the middle (125) and near the maximum (200) to measure peak power.

...

An important and troublesome observation of this study is that for these short 'explosive' trials the power measured by sensors on the handle differs strongly from the power displayed on the C2 performance monitor "..our observations indicate that the power output values displayed on the Concept II rowing ergometer underestimates the true power output by a factor of ~3."
I scrutinized the paper whether they use the same definition of power as C2 (i.e. power profile in the drive is 'averaged' over the full duration of the stroke), but I couldn't find specifics. It is known from other studies that for short bursts the C2 power and power from sensors on the handle can differ strongly, but I have never seen a factor of 3.
I am an experienced cyclist and familiar with cycling power and my ability. I recently got my Concept2 and was expecting to see higher power rowing than cycling. I always thought rowers put out more power than cyclists because their VO2max is, typically, higher. I was appalled at how low the power was. So appalled that I contacted Concept2 about the discrepancy. They convinced me their algorithm was accurate. Now I am not so sure. Perhaps their algorithm takes into account losses between the oar handle and the water, representing the power to the water which is what is needed to calculate pace.

The actual number isn't that important from a training perspective as long as it is reliable and reproducible in that bigger is always better. But, from a research perspective it could be important.

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