Just did an hour row, why is my watts so much lower than my bike?

[Nomath]

I am blown away at the choices C2 made in measuring power. Accurately measuring the power would have been so easy (and it didn't have to be measured at the handle).

I think that the way C2 measures power is very smart! It means that the machine is self-calibrating for changes in damper setting, elevation, barometric pressure, temperature, bearing friction in the flywheel, dust accumulation, air flow impediments when the machine is set close to a wall, etc.

I am very interested to hear how it could be done otherwise (i.e. not already applied in the Boyas paper).

[frankencrank]

That discrepancy is almost entirely due to the potential energy being put into the shock cord during the power phase reducing the power seen by the flywheel.

If the user doesn't get the work done on the bungee during the drive back on the recovery (which obviously would not be measured by the erg, but would still benefit the user) then the only place it can go would be to be converted into waste heat. One of these days I'm going to have to get a pyrometer and get before and after bungee cord temperature measurements. I bet it won't change much, if at all.

I am sorry, but the recovery benefit does not benefit the rower. It would only benefit the rower if it actually provided some power or reduced the effort of the power generating muscles. Add a bungie cord to the seat of the shell that does a similar thing and see if it has no effect.

In cycling, when lifting the leg gravity reduces the force the muscles apply to the pedal, similar to the shock cord on the ergometer but that potential energy that is put into lifting the leg is returned to the bike on the down stroke so there is little or no loss. Nothing is returned to the rowing ergometer. It is a total loss.

Put your pyrometer on the fan, bet you find it doesn't change much at all either. Such would be a waste of time unless you were in a completely controlled environment. Power is simply force times speed. The power lost by the shock cord resistance is pretty easy to calculate. Force (which seems to me to be about 10 lbs on average but it doesn't matter the exact number, it is what it is) times speed averaged over the percentage of time. The loss will depend only on the stroke rate and the stroke distance.

[frankencrank]

This discrepancy is largely not due to the movement of the rower during the recovery, but probably caused by losses in the drive mechanism of the RowErg.

That discrepancy is almost entirely due to the potential energy being put into the shock cord during the power phase reducing the power seen by the flywheel. If they would have varied the stroke rate in their study they would have seen the discrepancy vary.

Read the paper! The investigators increased the power stepwise from quite low to exhaustive. The stroke rate was left free to the subjects. It is very likely that in this incremental test the stroke rate also varied from low to high. The data do not indicate that the discrepancy varies with power.

You are assuming the stroke rate must have varied. I am simply saying the math says that the shock cord losses must vary with stroke rate and the fact they observed losses did not suggests the stroke rate was pretty constant.

[frankencrank]

I am blown away at the choices C2 made in measuring power. Accurately measuring the power would have been so easy (and it didn't have to be measured at the handle).

I think that the way C2 measures power is very smart! It means that the machine is self-calibrating for changes in damper setting, elevation, barometric pressure, temperature, bearing friction in the flywheel, dust accumulation, air flow impediments when the machine is set close to a wall, etc.

I am very interested to hear how it could be done otherwise (i.e. not already applied in the Boyas paper).

Measuring power in something like an ergometer is pretty easy. Instantaneous power is simply the force times the speed at any given time. Average power is the average of all those instantaneous powers over time. In a rowing ergometer it is especially easy as the force is constrained to come from one direction. If C2 simply put a strain gauge in the support for the fan they could calibrate the measured strain to reflect handle force provided by the rower (by subtracting the force provided by the shock cord) and then it is a simply necessary to measure chain speed which can be done in many various ways.

[Tsnor]

In cycling, when lifting the leg gravity reduces the force the muscles apply to the pedal, similar to the shock cord on the ergometer but that potential energy that is put into lifting the leg is returned to the bike on the down stroke so there is little or no loss. Nothing is returned to the rowing ergometer. It is a total loss.

You use leg power to pull yourself back up to the catch, and its not trivial especially at high rates. Muscles used during recovery "The triceps engage to push the arms forward and away from the body. The abdominals flex the torso forward, and the hamstrings and calves contract as you slide up to the catch." ** If something reduced the effort of getting back to the catch it would help the rower. There is a difference rowing with feet strapped in vs no straps because different technique is required to pull yourself back to the catch. Try rowing strapless at high rates if you think getting back to the catch is free.

** https://www.concept2.com/indoor-rowers/ ... scles-used

[frankencrank]

In cycling, when lifting the leg gravity reduces the force the muscles apply to the pedal, similar to the shock cord on the ergometer but that potential energy that is put into lifting the leg is returned to the bike on the down stroke so there is little or no loss. Nothing is returned to the rowing ergometer. It is a total loss.

You use leg power to pull yourself back up to the catch, and its not trivial especially at high rates. Muscles used during recovery "The triceps engage to push the arms forward and away from the body. The abdominals flex the torso forward, and the hamstrings and calves contract as you slide up to the catch." ** If something reduced the effort of getting back to the catch it would help the rower. There is a difference rowing with feet strapped in vs no straps because different technique is required to pull yourself back to the catch. Try rowing strapless at high rates if you think getting back to the catch is free.

** https://www.concept2.com/indoor-rowers/ ... scles-used

Ugh, if you haven't noticed, the slide is usually level. The leg power needed to get yourself back to the catch is simply the power needed to accelerate up to speed and maybe a small bit to crunch up at the end. Those are completely different muscles than those used to generate power and are a tiny addition to the overall oxygen need. While that might "help the rower" it does nothing to help the power generating muscles. The shock cord reduces the overall power measured from what the rower is actually doing (at least the way C2 measures it).

Let me add, those recovery muscles are completely underutilized but, with modification, could be used to generate substantial additional power. viewtopic.php?f=3&t=200997

[frankencrank]

Let me add this. This is a simple math problem. Rowers generally use more oxygen than cyclists. Rowers (at least on ergometers) generally have lower power than cyclists. Oxygen correlates with energy expenditure. Account for the difference.

[Tsnor]

Measuring power in something like an ergometer is pretty easy. Instantaneous power is simply the force times the speed at any given time. Average power is the average of all those instantaneous powers over time. In a rowing ergometer it is especially easy as the force is constrained to come from one direction. If C2 simply put a strain gauge in the support for the fan they could calibrate the measured strain to reflect handle force provided by the rower (by subtracting the force provided by the shock cord) and then it is a simply necessary to measure chain speed which can be done in many various ways.

In bicycles the strain gauge used is +/- 1-2%. Could you imagine the trouble if some ergs reported split times 1-2% faster than other ergs? https://roadcyclinguk.com/how-to/fitnes ... think.html

Getting a strain gauge that accurate is expensive. (I don't know why, scale are cheap, bike power meters are not). Bike systems are $300-$1000 US. Not exactly a cheap upgrade for a $900 C2 erg.

The solution used by C2 is elegant. The patent is now expired so others are copying it.

I'd guess the only reason the power reported is off by so much is Concept2 chose to make the reported splits compatible with older C2 rowers that used a different approach to measuring power/splits.

[Tsnor]

Let me add this. This is a simple math problem. Rowers generally use more oxygen than cyclists. Rowers (at least on ergometers) generally have lower power than cyclists. Oxygen correlates with energy expenditure. Account for the difference.

The difference is misuse of the word "power". In your example the rowers do not have lower power. They have lower net power delivered because rowing is less efficient than cycling. Your example rowers actually produced more gross power than the cyclists given they used more oxygen. The difference between gross and net power is the wasted effort. Rowing is less energy efficient than cycling.

Mountain bikes are less efficient than road bikes. At the same speed and conditions the same bike rider will consume more oxygen on a mountain bike than on a road bike. We don't declare the power output of the rider lower because he is riding a less efficient bike. The FTP of a cyclist doesn't change when he shifts from a mountain bike to a road bike. The actual net power than can be delivered by that cyclist on a mountain bike to (for example) a towed trailer will be lower than the net power delivered by the same cyclist on a road bike, but that doesn't change the power output of the rider.

[frankencrank]

Let me add this. This is a simple math problem. Rowers generally use more oxygen than cyclists. Rowers (at least on ergometers) generally have lower power than cyclists. Oxygen correlates with energy expenditure. Account for the difference.

The difference is misuse of the word "power". In your example the rowers do not have lower power. They have lower net power delivered because rowing is less efficient than cycling. Your example rowers actually produced more gross power than the cyclists given they used more oxygen. The difference between gross and net power is the wasted effort. Rowing is less energy efficient than cycling.

Mountain bikes are less efficient than road bikes. At the same speed and conditions the same bike rider will consume more oxygen on a mountain bike than on a road bike. We don't declare the power output of the rider lower because he is riding a less efficient bike. The FTP of a cyclist doesn't change when he shifts from a mountain bike to a road bike. The actual net power than can be delivered by that cyclist on a mountain bike to (for example) a towed trailer will be lower than the net power delivered by the same cyclist on a road bike, but that doesn't change the power output of the rider.

Sorry, you are misusing terms. Power is a measure of work done per unit time. Rowers do not do more gross power because they use more energy. Power is work done per unit time. Your term "net power" is the only power that matters in competition as that is the "power" that makes the shell move and represents the work done by the rower. Efficiency is the ratio of the energy consumed vs the energy converted into useful work.

So, why is rowing less efficient than cycling? At least on the ergometer, the shock cord counts for some of the inefficiency as it lowers the measured power from what the rower is actually doing (at least the way C2 measures it). And, if you would watch my video, you would understand some of the inefficiencies of rowing that can be minimized by technique changes. viewtopic.php?f=3&t=200997

Your cycling examples make no sense to me.

[frankencrank]

Measuring power in something like an ergometer is pretty easy. Instantaneous power is simply the force times the speed at any given time. Average power is the average of all those instantaneous powers over time. In a rowing ergometer it is especially easy as the force is constrained to come from one direction. If C2 simply put a strain gauge in the support for the fan they could calibrate the measured strain to reflect handle force provided by the rower (by subtracting the force provided by the shock cord) and then it is a simply necessary to measure chain speed which can be done in many various ways.

In bicycles the strain gauge used is +/- 1-2%. Could you imagine the trouble if some ergs reported split times 1-2% faster than other ergs? https://roadcyclinguk.com/how-to/fitnes ... think.html

Getting a strain gauge that accurate is expensive. (I don't know why, scale are cheap, bike power meters are not). Bike systems are $300-$1000 US. Not exactly a cheap upgrade for a $900 C2 erg.

The solution used by C2 is elegant. The patent is now expired so others are copying it.

I'd guess the only reason the power reported is off by so much is Concept2 chose to make the reported splits compatible with older C2 rowers that used a different approach to measuring power/splits.

I am confused. What is the accuracy claim of C2 for the PM5? What is the variation of shock cord resistance between units? Does shock cord resistance change as the unit gets older?

Bicycle power meters are complicated, being attached to rotating pieces and exposed to all sorts of inclement weather conditions. What I am talking about is an incredibly simple set-up that can be protected from the weather.

[Carl Watts]

Ugh, if you haven't noticed, the slide is usually level.

No its not, if you have noticed with a clean slide and rollers the seat runs towards the front of the rower. There is a deliberate rise incorporated in the design to the rear. This coupled with the energy stored in the bungee helps you get back during the recovery, otherwise your 100% using what feels like horribly inefficient muscles like the hamstrings in the backs of your legs.

The major difference in power loss between the bike and the rower is accelerating the bodyweight. If I moved to slides I would expect a significant improvement in my performance. My current bodyweight is now 110Kg. I'm now finding it easier to row at lower ratings with more power per stroke because trying to accelerate the weight for anything other than short sprints is becoming hard work. If I moved to slides I would expect to pickup at least 300meters on my 30minute for the same heartrate. I have been very tempted to try some slides, however the cost coupled with the floor space required has put me off. That extra 20-30W wasted going up and down the slide would be getting to the flywheel instead with slides or rowing on a Dynamic. Depending on how good your technique was perhaps just about all that wasted energy would be getting to the flywheel.

[Carl Watts]

I am blown away at the choices C2 made in measuring power. Accurately measuring the power would have been so easy (and it didn't have to be measured at the handle).

I think that the way C2 measures power is very smart! It means that the machine is self-calibrating for changes in damper setting, elevation, barometric pressure, temperature, bearing friction in the flywheel, dust accumulation, air flow impediments when the machine is set close to a wall, etc.

I am very interested to hear how it could be done otherwise (i.e. not already applied in the Boyas paper).

C2 did the best job ever in the way it measures the power, its way better than a bike that ends up having to use and electric motor on the cranks to calibrate it. Find me something else that doesn't need constant "Calibration" or stuffing about with to keep it calibrated.

The whole idea is you can compare one Erg directly with another, its not designed to compare a Erg to a Bike.

[frankencrank]

The whole idea is you can compare one Erg directly with another, its not designed to compare a Erg to a Bike.

It gives a power number. It is going to be compared to a bike power number.

[frankencrank]

Ugh, if you haven't noticed, the slide is usually level.

No its not, if you have noticed with a clean slide and rollers the seat runs towards the front of the rower. There is a deliberate rise incorporated in the design to the rear. This coupled with the energy stored in the bungee helps you get back during the recovery, otherwise your 100% using what feels like horribly inefficient muscles like the hamstrings in the backs of your legs.

The major difference in power loss between the bike and the rower is accelerating the bodyweight. If I moved to slides I would expect a significant improvement in my performance. My current bodyweight is now 110Kg. I'm now finding it easier to row at lower ratings with more power per stroke because trying to accelerate the weight for anything other than short sprints is becoming hard work. If I moved to slides I would expect to pickup at least 300meters on my 30minute for the same heartrate. I have been very tempted to try some slides, however the cost coupled with the floor space required has put me off. That extra 20-30W wasted going up and down the slide would be getting to the flywheel instead with slides or rowing on a Dynamic. Depending on how good your technique was perhaps just about all that wasted energy would be getting to the flywheel.

You feel like you need that "help" to get back on the recovery? LOL
That rise on the power stroke, again, reduces the power seen on the PM5 compared to what the rower is actually doing.

It isn't clear how much the kinetic losses of body accelerations is contributing to the differences. Let's stay with competitive rowers, who probably average around 30-34 SPM while racing. If we assume most of the acceleration comes from the legs (the arms just maintaining speed) then we see that acceleration occurs in about 18 inches or so. Cyclists, however, are accelerating substantially less mass (perhaps 1/4-1/3 that of the rower) through a smaller distance but at a substantially higher frequency (twice a cycle when a cycle recurs on average around 90 times a minute). The energy cost varies with the cube of these frequencies. Minimizing these losses while trying to maximize the effective power is one key to improving efficiency and power through technique change. viewtopic.php?f=3&t=200997

Slides would be an effective way of improving power. The problem with slides is it doesn't reflect the water, a sort of cheating. Paying attention to slide speed to minimize losses is not cheating.