Trying to understand SPM

[Tinus]

...The PM monitor is essentially measuring power and using this to determine your pace. SPM is just an...

Well, technically this is not entirely correct. The PM monitor measures speed and uses this to determine power instead of the other way around. This means that the measure of power is not always correct. Just visualize the first few strokes, they require a lot power but the monitor displays low power because the speed is low. It takes the speed and calculates this into power assuming constant speed ignoring acceleration. It would also be very difficult to determine distance/speed on the erg depending on a measure of applied power since the boat has (almost) constant speed but power is applied non constant (namely only during the drive).

Because the erg essentially measures speed and not power it is possible to optimise rower power input for the same average speed as determined by the monitor. In order to do this you need a higher stroke rate because the root mean square speed will be lower. The same speed on the monitor but at a higher stroke rate requires less power. (This only means efficiency is best at higher stroke, it is obvious that at some point these higher drag and/or rate are not good because the higher efficiency is counteracted by the rower being less able to sustain or apply power.)

By the way, my vote goes to spm 30+ for any piece... sprint to marathon. From a certain perspective delivered power is just power per stroke times strokes per minute and so stroke rate does influence pace. You have to work on both in order to increase performance.

[NELSON]

My 2cents worth. I have always rowed at a 34-36 SPM, from the 1000m-FM. The only exception is the 500M and that's a LET IT ALL HANG OUT pace, over 40SPM. It has served me well over these past years. I have never had the pure strength to row at those low SPM. I do sometimes train in the 20 SPM range but not often. Find whats comfortable and stick with it, let your whole body dictate your natural rhythm.

[Carl Watts]

I think you need to perhaps factor in age & weight into the equation in that you no longer have the power per stroke so you have no choice but rate up to compensate.

With some of the paces in the sigs I'm down at 15 SPM, the only time I rate at 32 SPM is the 500M. Simply not required for my distance work, 20 SPM works for me and 21 SPM appears to be the most efficient in terms of pace/HR at present.

With the huge variation of ages, weights and physical fitness levels here there will be no set SPM's, all I can say is that with continued training the trend for me has been that the SPM falls as your pace also improves. I started 6 months ago rating at 27-28 SPM. Also the more you train the more you are aware of your bodies limits and become better at predicting a pace and SPM to meet your goals.

I would also never directly compare anything ever done on an ERG to OTW, I'm pretty sure that any elite OTW rower will tell you the same.

[jamesg]

The PM monitor measures speed ; well yes, the speed of the flywheel. Then, by observing flywheel slow-down during the recovery it calculates the work done against the atmosphere over the entire stroke; which is equal to the work we put in. From this, and knowing when the stroke begins and ends, the input Power can be calculated; and hence the (fictitious) boat speed and pace.

Boat speed is related to power, in the C2 world, via a cubic function (W=kV^3), and pace is the inverse of speed. Which is what makes life difficult for those who want to relate pace and rating.

For this it's easier to watch Watts and keep the Watt/Rating ratio nearly constant, at all ratings. At least you know how much work you've put into the handle and can, if you so wish, train as you would race.

[hjs]

I think you need to perhaps factor in age & weight into the equation in that you no longer have the power per stroke so you have no choice but rate up to compensate.

With some of the paces in the sigs I'm down at 15 SPM, the only time I rate at 32 SPM is the 500M. Simply not required for my distance work, 20 SPM works for me and 21 SPM appears to be the most efficient in terms of pace/HR at present.

With the huge variation of ages, weights and physical fitness levels here there will be no set SPM's, all I can say is that with continued training the trend for me has been that the SPM falls as your pace also improves. I started 6 months ago rating at 27-28 SPM. Also the more you train the more you are aware of your bodies limits and become better at predicting a pace and SPM to meet your goals.

I would also never directly compare anything ever done on an ERG to OTW, I'm pretty sure that any elite OTW rower will tell you the same.

You are thinking wrong, rating low in traini g may be fine and otw rowers row most of there training at low rates in teh 18/20 range, but that is to focus on technique and developing a strong stroke.

For racing nevertheless, rating low is never the way to go, every otw rower rates high during racing. For a 2k you need to rate at least 30 and proberly better 32/34. For a 500 meters sprint 40 as a minimun.

[Tinus]

The PM monitor measures speed ; well yes, the speed of the flywheel. Then, by observing flywheel slow-down during the recovery it calculates the work done against the atmosphere over the entire stroke; which is equal to the work we put in. From this, and knowing when the stroke begins and ends, the input Power can be calculated; and hence the (fictitious) boat speed and pace.

Boat speed is related to power, in the C2 world, via a cubic function (W=kV^3), and pace is the inverse of speed. Which is what makes life difficult for those who want to relate pace and rating.

For this it's easier to watch Watts and keep the Watt/Rating ratio nearly constant, at all ratings. At least you know how much work you've put into the handle and can, if you so wish, train as you would race.

No no no, the monitor really measures speed as it is. The distance or speed which the monitor shows is exactly linearly related to the number of revolutions or velocity of the flywheel (times the cube root of the drag factor).

- The monitor does measure flywheel slow down during the recovery. But it does not use this to calculate the work done, it only calculates the drag factor. The dragfactor and the speed of the flywheel are enough to calculate the equivalent of boat speed.

- The monitor is able to present the data in units of power but this does not mean that this also the same as power input, instead it is the equivalent of speed expressed in units of power. Speed and power are not directly related by (W=kV^3). If you are accelerating (for instance at the start) then you need more power input for the same average speed. The monitor does not show this effect because it measures speed and not power. The equation is only valid to be used because in rowing one mostly moves at steady state, however there is a small fluctuation of speed because the power input is not constant. I've once calculated the effect of rate on this "error" and it did have a small percentage of influence.

[Steelhead]

...The PM monitor is essentially measuring power and using this to determine your pace. SPM is just an...

Well, technically this is not entirely correct. The PM monitor measures speed and uses this to determine power instead of the other way around. This means that the measure of power is not always correct. Just visualize the first few strokes, they require a lot power but the monitor displays low power because the speed is low. It takes the speed and calculates this into power assuming constant speed ignoring acceleration. It would also be very difficult to determine distance/speed on the erg depending on a measure of applied power since the boat has (almost) constant speed but power is applied non constant (namely only during the drive).

Because the erg essentially measures speed and not power it is possible to optimise rower power input for the same average speed as determined by the monitor. In order to do this you need a higher stroke rate because the root mean square speed will be lower. The same speed on the monitor but at a higher stroke rate requires less power. (This only means efficiency is best at higher stroke, it is obvious that at some point these higher drag and/or rate are not good because the higher efficiency is counteracted by the rower being less able to sustain or apply power.)

By the way, my vote goes to spm 30+ for any piece... sprint to marathon. From a certain perspective delivered power is just power per stroke times strokes per minute and so stroke rate does influence pace. You have to work on both in order to increase performance.

You can illustrate this by just sitting on the seat and pulling the handle as fast as you can; your SPM goes up to around 50 or so and your meters are flying by, but it is meaningless. I like the power stroke using my legs to control the SPM instead of my arms. You can do a sub 2:00 split at 18 SPM for example while the guy next to me is doing the same at 35 SPM. The slower I go the faster I go is what I have found.

[Tinus]

You can illustrate this by...

By this you mean the part

(This only means efficiency is best at higher stroke, it is obvious that at some point these higher drag and/or rate are not good because the higher efficiency is counteracted by the rower being less able to sustain or apply power.)

instead of the entire quote?

[jamesg]

No no no, the monitor really measures speed as it is. The distance or speed which the monitor shows is exactly linearly related to the number of revolutions or velocity of the flywheel (times the cube root of the drag factor).

The flywheel runs at around 700 rpm or say 12 rps. The cube root of DF might be 5. So you're saying the distance (or speed, of what? the erg goes nowhere) is 5x12 = 60. What units? If we're in a cgs system, this product could be cm or cm/s? I can't see anyone rowing at 0.6 m/s or, in an mks system, 60 m/s.

Rpm has dimensions 1/T. For the product Rpm x DF^(1/3) to be a speed (L/T), DF would necessarily have dimensions L^3, that is it would be a volume. This seems unikely enough to be not worth examination. Drag implies deceleration, so there must be a T in it somewhere.

[Citroen]

What units?

Whenever you're stuck for a unit use inverse square farads.

[Carl Watts]

Best to keep it simple, it takes x amount of power to increase the RPM's of the flywheel, one of the variables in the drag factor equation must be using the reduction of RPM's or decelleration of the flywheel from one stroke to the next ? the end result after a load of math, the full understanding of which is not going to help you row faster, but maintaining your ERG in top shape & training will, is that you end up with the all important "exponential shaped" curve on page 3 of the following which explains why you need so much more power to go that bit quicker in terms of pace. This looks similar to the required power of a car vs top speed which is a cubic law due to the nature of air resistance, which put simply in rowing terms is for any given pace to then row twice as fast you need eight times the power transfered to the flywheel.

Table 1 is a great reference for what your up against when trying to increase your pace. It probably also explains why your Heart Rate just takes off trying to improve your pace by those extra few seconds.

http://concept2.co.uk/assets/docs/schoo ... sheet3.pdf

This also contains all sorts of other information on page 4 as to the "Optimum stroke rate range".

Worth a read.

[snowleopard]

http://home.hccnet.nl/m.holst/ErgoDisp.html

[Tinus]

No no no, the monitor really measures speed as it is. The distance or speed which the monitor shows is exactly linearly related to the number of revolutions or velocity of the flywheel (times the cube root of the drag factor).

The flywheel runs at around 700 rpm or say 12 rps. The cube root of DF might be 5. So you're saying the distance (or speed, of what? the erg goes nowhere) is 5x12 = 60. What units? If we're in a cgs system, this product could be cm or cm/s? I can't see anyone rowing at 0.6 m/s or, in an mks system, 60 m/s.

Rpm has dimensions 1/T. For the product Rpm x DF^(1/3) to be a speed (L/T), DF would necessarily have dimensions L^3, that is it would be a volume. This seems unikely enough to be not worth examination. Drag implies deceleration, so there must be a T in it somewhere.

P = kboat * Vboat^3 = kflywheel * Vflywheel^3

<->

Vboat = (Kflywheel/Kboat)^(1/3) * Vflywheel

It just depends on what you define as the drag constant. The value, Kf/Kb, in the second formula is dimensionless.

Maybe think about this problem: How does the concept monitor know how many meters you are rowing during the recovery? Does it stop the boat and make an update of the covered distance only each time at the end of the stroke when it is said to be calculating power input? (it could do a very difficult calculation but it is more easy to just take the number of flywheel revolutions. Integration of the above equation leads to: Distanceboat = (Kflywheel/Kboat)^(1/3) * Distanceflywheel)

The flywheel does more like 40 rps.

[Tinus]

http://home.hccnet.nl/m.holst/ErgoDisp.html

Another complication is that the equations (3) and (4) refer to instantaneous values. During the pull the power is not constant and during the recover the power is nil. The power shown on the display (the central window) is almost certainly the power delivered during one complete cycle of pull and recover. At the end of the pull (handle at the stomach) the value of the power is refreshed. Compare this situation with a four-stroke piston engine. Only one out of four strokes produces work; this amount of work is divided by the total cycle time and that is ‘the’power.


It is possible that Concept has programmed the following calculation in the processor:

The concept monitor does not calculate power.

Proof: accelerate or decelerate and find out that the displayed power is high or low depending on the speed being high or low and not depending on the stroke power input being high or low. The second term in the integral is not taken into account.

[Citroen]

Most of the Concept2 maths (from the days of PM2s on model Bs) is discussed in some detail at http://www.atm.ox.ac.uk/rowing/physics/ergometer.html