Concept2 Forum

The drag factor is a recurrent issue on this forum. Recently I found two scientific studies in which a group of young college rowers was subjected to an incremental step-wise exercise to exhaustion at two widely different drag factors: 100 and 150. The effects on power, pace and stroke rate were measured, but also physiological parameters such as heart rate, ventilation rate, oxygen uptake and lactic acid built-up. I think the results are very interesting in understanding what drag factors do. I prefer to start a new topic, which makes it easier to retrieve and keeps the discussion focused on the issues mentioned in the title. Also my text is too massive to dump it in someone else’s topic.
I am happy to answer any questions as long as they relate to these two scientific papers or my presentation of the results. I will not reply to personal experiences or speculations.

The first paper, published in 2008, is titled Effects of Drag Factor on Physiological Aspects of Rowing. At the time it was briefly mentioned on this forum in 2008, but not discussed in depth. In 2012 the same first author published a paper titled Effects of Stroke Resistance on Rowing Economy in Club Rowers Post-Season. It is to a large extent a repeat of the first study with a different group of participants, addressing some additional questions. I could download the two papers free of charge, but I am not sure whether this applies to anybody. Send me a personal message with your email if you cannot download and are interested in a copy (links are in the next post).


Browsing through these papers, you will have difficulty to grasp and understand the effects. This is mainly because the results are condensed in two tables (Table 2 in the 2008-paper and Table 1 in the 2014-paper). So many effects are quantified by means and standard deviations, that it hard to see the trends. So what I did is to collect all the data in my computer and plotted them in specific graphs. For presentation in this topic I chose the data from the 2012-paper, which is slightly more extensive. However, there is not much difference with graphs made from the 2008-database.

Participants
5 male and 7 female members of the Northern Michigan University rowing club. They were experienced non-elite club rowers. Age 20.3 ± 0.4 yrs (notation: mean ± standard deviation). Height 170.9 ± 2.2 cm. Weight 72.7 ± 2.1 kg. Rowing VO2max 3.2 ± 0.2 L/min. All participants were familiar with the Concept2 erg and used it regularly for training.

Exercise
Each participant rowed at a drag factor of 100 and 150 in random order. For each drag factor the exercise consisted of 7 stages of 3 minutes and 1 minute rest in-between. The intensity increased stepwise over stage 1-6 by requiring the rower to maintain an individualized predetermined 500m pace. The individualized pace decreased by 6 sec per stage. In stage 7 the participant was required to self-select and maintain their fastest possible pace for the 3-min period.
Each participant was allowed to self-select the stroke rate.
Heart rate (Polar sensor), power, pace and stroke rates for each stage were collected as usual by the PM3 monitor. During rowing, breath-by-breath expired air was analysed (oxygen and CO2). In each 1-min rest blood lactate concentration was measured by puncturing a fingertip and collecting blood in a sample capillary.

Power output
Since each participant had an individualized pace protocol, the results in pace and power per stage are averages. The graph below shows the average power. The drag factor has virtually no effect on power output. This should not come as a surprise for stage 1-6, since pace and hence power were predetermined, although different per individual. So the averages per stage at DF=100 and DF=150 should be the same. That this is almost so, shows that the participants did what they were requested to do. That the results for stage 7 -the all-out stage- is also nearly the same is more of a surprise. The data suggests that at DF=150 the participants were able to generate a tiny bit more power.



Effect on Stroke Rate
Stroke rate was left free. It should not come as a surprise to any indoor rower that the resistance feels higher at a higher drag factor, so the drive phase will be somewhat slower. But how much? The figure below gives an answer. The difference is less than I expected: about 1 stroke/min in stage 1-6 and 2.5 strokes/min in the final all-out stage.




Effect on heart rate
It often helps to make an analogy. To me power output in rowing is like the speed of a car: it’s the ambient performance. For how much the engine is strained by this performance, you don’t look at the speedometer but at the rev-counter. For a rowing engine the rev-counter is the heart rate. The figure below shows the effect on HR of the successive stages at the two drag factors.

I believe here we have come to an effect that is less intuitive. What the figure shows is that the participants could maintain a certain pace/power at a lower heart rate using the high drag factor. The difference is consistent over the full power range, about 3 bpm. Is that much? Yes, I think so! In the second figure below I have plotted pace versus heart rate. What you see is an almost linear drop in pace with an increase in heart rate. The slope is about -0.6 sec per beat. So 3 bpm corresponds to about 2 seconds faster pace at DF=150.







Ratio Watts and stroke rate vs relative heart rate

In the following graphs I like to abstract a bit from the group of participants by comparing effects as a function of the relative heart rate, i.e. the heart rate as a percentage of HRmax. I believe that using the relative-HR makes the graphs more universal. I took the heart rate registered at the end of the all-out section-7 at DF=100 as HRmax. This is not strictly the case as the stage lasted only 3 mins, which is a bit short. On the other hand, the participants had already rowed for 21 min at step-wise increasing intensity, which is an often-used protocol for measuring HRmax. And the average HRmax of 193 bpm is in reasonable agreement with what age-related formulas predict for groups (i.e. not each individual).

From the data collected by the C2 performance monitor it is easy to calculate the ratio of Power in Watts and Stroke rate. This ratio is a measure for the energy per stroke. Multiply the ratio by 60 and you get the energy in Joules per stroke. The figure below shows the results. At the same relative heart rate, the rowers produced about 30 Joules per stroke more at DF=150 than at DF=100.





Oxygen uptake vs relative Heart rate

The following figure shows the oxygen uptake. For stages 1-5 there is no appreciable effect of the damping factor. At high intensity, it seems that the body needs somewhat less oxygen for the same power output at DF=150. Hence it seems that the human body becomes slightly (about 0.3%) more efficient at DF=150 compared to DF=100.



Ventilation vs relative Heart Rate
Ventilation is the volume of air that the participants exhale. Of course, some oxygen is extracted in our lungs and is replaced by carbon dioxide (CO2). Since oxygen is roughly replaced 1:1 by CO2, we may roughly equate it with the volume of air inhaled.
The figure shows that, except for stage-5, all data points seem to lie on a single curve: relative heart rate and ventilation seem closely linked.



Oxygen consumption vs Ventilation
We now come to some observations that, for me, were quite surprising. Since we already saw that the drag factor had little effect on oxygen consumption and neither on ventilation, the surprise is more in the quantitative relation between these two variables.
What the graph below shows is that the oxygen consumption increases with ventilation – no surprise. However, the increase is not proportional. At the lowest intensity, the average inhaled volume is 40 liter/min and about 1.7 liter/min of oxygen is consumed. When the ventilation increases to 60 L/min, a factor of 1.5 increase, the oxygen consumption has increased to about 2.3 L/min, a factor of 1.35. With ever higher ventilation, the extraction of oxygen gets proportionally lower. Maybe not a big surprise, because the breathing gets faster.

But there is another point. Air contains about 21% of oxygen. 40 liters of air contain about 8.5 liters of oxygen. The consumption is only 1.7 L/min, i.e. only 20% of the available oxygen is extracted. The remainder of the oxygen, roughly 80%, together with the inert nitrogen and the produced CO2 is exhaled. This is a pointer to the mechanism that becoming breathless is not so much due to a shortage of oxygen in our lungs but rather due to an excess of carbon dioxide.




Respiratory Exchange Ratio vs relative Heart rate
The RER is the ratio of the amount of carbon dioxide (CO2) produced in burning nutrients to oxygen (O2) used. Burning hydrocarbons, e.g. glucose, results in a RER of 1, i.e. the number of oxygen molecules used equals the number of molecules of carbon dioxide produced. ‘Fats’ have considerably more carbon and hydrogen but less oxygen than hydrocarbons. The RER from burning fats is around 0.7. The RER can get above 1 if nutrients are oxidized incompletely, often resulting in the formation of lactic acid which accumulates in the blood. The acid shifts the so-called bi-carbonate buffer system which releases CO2, stored as a bicarbonate, into air. The RER value at rest is usually 0.78 to 0.80. For further details see Wikipedia.

The figure below shows the RER as a function of the relative heart rate. It shows that at about 85% of HRmax the ratio rises above 1, meaning that the mechanisms of acidification on the bloods set in. This point will probably depend on the duration of the stage. At exhaustion, RER has become near 1.2 which indicates substantial lactate accumulation. The RER curve for DF=150 lies slightly higher than for DF=100. But if we would compare RER at the same power, the curves do merge to one.




Blood lactate concentration vs relative Heart rate
What was already surmised from the precious figure is shown in the next figure below. Up to about 80% of HRmax the blood lactate level is constant, but it starts to rise steeply at about 85%.
For road cyclists a level below 2 mmol/L (or 2mM ; M for molar is the abbreviation for mol/L) is typical for basic endurance training. Between 3-6 mM occurs in competitions. A level >6 mM is typical for short peaks. Tolerance for lactic acid levels is known to differ amongst individuals. In training of elite cyclists, the improvement in power at 4 mM is taken as a measure of success.






Final comment
The effects of the damping factor on performance and physiological parameters are not big. I had expected bigger effects, because a haul at DF=150 feels quite different from DF=100. The main effect is on stroke rate. It is interesting to speculate on results at DF=120, which is often advised as the most agreeable setting. Is it just a linear interpolation between the two settings of this study or is there an optimum between the two settings, hence a more or less parabolic shape ? Unfortunately, a drag factor setting near 120 was not included in these studies. The question remains open.

Due to limitations of the Forum server (max 10 URLs in one post), I had to delete 3 useful links.
The first is to a previous discussion of the 2008 paper on this forum :
viewtopic.php?f=3&t=6818

The link to the 2008 paper :
https://www.academia.edu/1890092/Effect ... _of_rowing

The link to the 2012 paper :
https://www.researchgate.net/publicatio ... ost-Season

Very interesting, thanks.

As I have experimented a lot with different drag factors over the years, and in more recent years due to lowering the drag due to injury, I personally have found that there is a perception and psychological effect that comes into play.

About three years ago I jumped on a gym rower and forgot to check the drag, I rowed a steady 30 minutes and really enjoyed it. When I finished I knew it was a heavier drag than usual, and it turned out to be 202 (if nothing else, a great sign of how well maintained the ergs were). When I tried to replicate it a few days later, when I knew the drag was a lot higher, I couldn't replicate the same feeling.

I have found that if the stroke feels heavy, there is a subtle change in my mindset, ie an extrapolation of this effort concluding in it being considered unsustainable.

Imo, there is a very significant overlap of what is physically manageable / possible and what is perceived as being manageable / possible.

understanding what drag factors do.

Adjusting drag factor lets us set the machine impedance to suit our speed/force characteristic and so ensure maximum power transfer. It's odd that the "researchers" did not know this, so used only two data points. However they were surprised, which is what research is for.

I suggest that you read the Introductions of the two papers!

In my post I concentrated on the graphical presentation of the results. I didn't discuss the objectives of the researchers. Briefly, the authors did know about the recommendations and use of the drag factor. The first author, according to his CV, was at the time of these studies active in rowing, competing and coaching. The introduction points out that many scientic papers about ergometer rowing don't even mention the drag factor setting! The purpose of these two studies was to test the effect of resistance (drag factor) on the physiological responses. As far as I know, these papers are the only published studies where the drag factor was varied on purpose. You may deplore, as I do, that they haven't included a third central setting, but having the results at two settings that bracket the recommended range is a significant advance in our knowledge.

For example, considering that the 'feel' of a haul at DF=100 is very different from DF=150 and the movements will also be different, I find it quite amazing that at the same power the blood lactate levels are virtually the same. It is known from cycling that a trained cyclist can sustain a blood lactate of 4 mM ("in the red") for some 10 minutes. In fact, power @ 4mM lactate is often taken as a person's figure of merit.



I have read several studies of the pedalling frequency of road cyclists. It's known that the most economical pedalling frequencies for stationary cycling lie between 50 and 80 rpm. Most economical means: highest ratio of power output over nutritional energy consumed. Recreational riders prefer to pedal on the lower end of the range. However, competitive cyclists prefer to use pedalling rates of 90-105 during prolonged exercise at high intensity. What these studies do is to look at heart rates, ventilation, oxygen consumption, blood lactate, etc to analyse this choice. I have never seen impedance introduced as a useful concept.

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.

The participants were all young students aged roughly between 18 and 25 yrs. They were divided in 3 groups according to their physical activity in sports : inactive (15 men, 12 women), active (16 men, 20 women) and experienced rowing club members (15 men, 9 women).
The test consisted of trials at the 3 different drag factor setting separated by 3-minute rest periods. Each trial consisted of 6 introductory strokes followed by 6 all-out strokes. The order in the 3 trials was random. Before the trials each participant had a general warm-up procedure on a stationary bike, body stretchings and a comfortable 5 min familiarization with the rowing ergometer. More details in the paper

Specifically for measuring peak power, the Concept2 ergometer was equiped with additional force sensor and a displacement sensor in the handle. These two sensors enabled to calculate the instantaneous power (power = force x speed).

I plotted the results from Table 2 in the graphs below. The first graph shows the power output per group. Because the group of experienced rowers was heavier (76 kg) than the other groups (69 and 71 kg, resp), it makes sense to compare the specific power (W/kg) in a second graph.





The power of 6 'all-out' strokes, at stroke rates between 35-45/min, hence during about 10 sec, is a measure of peak power. For me the most significant feature in the graphs is that experienced rowers can pull a high peak power at any drag factor setting. Inexperienced rowers benefit from a high drag factor setting.

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 looked for reference data for short term peak power. There is a graph in Cycling Analytics showing that a few elite cyclists can attain 1740W during 1 sec and about 1500W during 5 sec. The median value for short efforts is roughly 1000W. Also many Critical Power charts show a plateau of ~1200W for short efforts (less than 5 sec). So my guess is that the authors of the Zagreb paper, studying experienced club rowers rather than elite rowers, used a different power definition from Concept2.
This doesn't invalidate the observations on the effect of the drag factor.

underestimates the true power output by a factor of ~3."

Clearly the use of Power here is misleading: Work is what counts.

jamesg wrote: ↑

November 22nd, 2020, 3:49 am

Clearly the use of Power here is misleading: Work is what counts.

Why? Can you explain?

Work should be related to the relevant time span in which it was done. 250 Years ago James Watt used horsepower to compare the output of steam engines with the power of draft horses. It relates work (force x displacement) to time.



(picture from Wikipedia).

In rowing, power is calculated as work during the drive phase only, divided by the time of the whole rowing cycle. This is because the recovery phase is an indispensible part of the cycle. The slower the recovery is done, the lower the calculated power.

We rate the engine of motor bikes and cars in kW. Household tools like vacuum cleaners and loudspeakers are rated in W. Maximum human power depends strongly on duration. Peak power, i.e. max power during 1, 5 or 10 sec, is an important characteristic in many sports like jumping and throwing disciplines in athletics, cycling sprints, short distance speed skating, kayaking, volleyball, etc.

Adjusting drag has the effect of altering our combination of force and length, ie Work done. There seems to be little point in introducing an unknown, time, given that we can row at whatever rating we like.

Those tested apparently adjusted their techniques/ratings to get the best possible results whatever the drag. Well done them, wouldn't we all as far as pos. But what was the point of the tests then? To show that the impedance curve is flatter than we might expect? Rowing was never like lifting feathers or pulling barges.

Time is an essential element. E.g. if you speed up the recovery, in which no work on the flywheel can be done, the work done in the drive phase is divided by a shorter time for the whole cycle, hence a higher output power for the whole cyle.

Regarding the drag factor: as the drag factor goes up, force becomes more dominant in the power production and speed less. The graph shows that experienced rowers are able to deliver relatively more power at the lowest drag factor than the 'active' group. This is not because they are stronger per se, but because they are more skilled to effectively coordinate the movements of different body parts (legs, trunk, arms) if speed is high.

The point of the tests? To investigate the erg as a tool for measuring whole-body peak power and finding the best drag factor for that. Please read the paper.

This was very interesting. I did not read the source materials, just your summary. Would the following conclusions that would apply to my situation (I consider myself in the active group) be correct:

1. higher DF equals higher watts vs lower DF, hence faster splits.

2. higher DF equals lower HR at same power output as lower DF.

3. higher DF results in lower rating vs lower DF.

If the above conclusions are correct, then I think I should experiment with a higher DF.

mict450 wrote: ↑

November 23rd, 2020, 1:07 am

This was very interesting. I did not read the source materials, just your summary. Would the following conclusions that would apply to my situation (I consider myself in the active group) be correct:

1. higher DF equals higher watts vs lower DF, hence faster splits.

2. higher DF equals lower HR at same power output as lower DF.

3. higher DF results in lower rating vs lower DF.

If the above conclusions are correct, then I think I should experiment with a higher DF.

No, no and no.

The only certain thing a higher gives is slower movements. And the potential to row faster, but you still need the fitness and strenght to actually pull that off. There is no free lunch.

For short work/sprinting, the limiting factor is often speed of motion, a higher drag gives extra time to perform the stroke. A 100m almost always goes best at a higher drag.

hjs wrote: ↑

November 23rd, 2020, 4:07 am

mict450 wrote: ↑

November 23rd, 2020, 1:07 am

This was very interesting. I did not read the source materials, just your summary. Would the following conclusions that would apply to my situation (I consider myself in the active group) be correct:

1. higher DF equals higher watts vs lower DF, hence faster splits.

2. higher DF equals lower HR at same power output as lower DF.

3. higher DF results in lower rating vs lower DF.

If the above conclusions are correct, then I think I should experiment with a higher DF.

No, no and no.

The only certain thing a higher gives is slower movements. And the potential to row faster, but you still need the fitness and strenght to actually pull that off. There is no free lunch.

For short work/sprinting, the limiting factor is often speed of motion, a higher drag gives extra time to perform the stroke. A 100m almost always goes best at a higher drag.

Oh, crap!! Thought I was on to something. What's more troubling for me is coming to the wrong conclusion from the data & charts. Faulty thinking process. I guess that puts me that much closer to senility.

As long as you think it, you are not.

Think about it, in the very big picture, drag can vary from close to zero up to indefinite high. At zero you can pull as fast as you can, but still put zero air. So no reading.
At indefinite heigh, we can’t move at all, so again, we can’t do any work again.

So there are 2 limitations, 1 the speed of motion and two, the amount of drag. We need to find something thats optimal between the two. Think the key is to found in the speed of motion, that should be kind of natural. To fast will mean inefficient, to slow will mean, to much force needed.