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.
As long as you think it, you are not.