Comparing Watts

[chris5150]

Maybe a silly question but using watts as a measurement of power, are they the same ratio's whatever the discipline?

I have an SRM power meter on my bike, and quite comfortably put out 250 watts on that for say a couple of hours, but yet my time for a half marathon on the rower of 1.23.10 was at an average of 212 watts.
Note also that on the pace calculator 300 watts is equal to 1.45/500...that's quite a pace, break 7 mins per 2k.
Also note brad wiggins can pull 460 watts for time trials which in rowing terms would be some ridiculous time of 1.31 or something per 500...hard to pull , let alone sustain for an hour.
So how does generating watts on a rower compare to watts generated on a bike?

[Citroen]

You can't compare bike watts vs rower watts. There's too many variables.

[chris5150]

Ok....but watts as a measure or unit of power is surely the same thing, or is it not?...ie surely the calculation to come to the energy level use to generate a watt of power must be the same?
Can you expand on your answer as it has not really helped me understand anything about the differences?

[Citroen]

A watt is a unit of power, but the measurement of watts from exercise equipment is an inexact science.

Humans are also notoriously inefficient in getting the power from their muscles to the device they're driving. Then there's gears, bungees, chains, flywheels, pedals and other mechanics that add to the complexity.

That's before we look at the fact that rowing isn't comparable to cycling by any stretch. The movements are too far different: one leg at a time in a continuous motion (with a bit of pull up if your feet are tied to the pedals) with a high cadence (75-100) for bikes and both legs for the drive portion of the rowing stroke then nothing for the recovery at a much lower cadence (20-32). If you're not riding a fixie then it gets ever more complex when you add in the massive choice of (usable) gear ratios on a bike. I'm also going to ignore head and tail winds (which don't happen on a gym rower) as that pushes us to the realms of fluid dynamics.

As I said, there's too many variables.

[chris5150]

Ok thanks , but shouldn't equipment have a sort of standard measurement?...so a watt is a watt so to speak. I mean one horse power is one horse power no matter how its generated. Surely as far as cadence is concerned that's not an issue, as say doing something at 100 rpm at a lighter speed would still generate the same power as doing something at say 50 rpm at a heavier speed.
Also you can cancel out headwind /tailwinds etc because a power meter measures power put into the cranks so again incline & speed are all irrelevant to the calculation, its how much power you are putting into the pedals that's measured. I am not talking power per kg or anything like that, just purely the watts produced.
I just expected that regardless of what piece of equipment you use a watt of power generated from the human body would be measured so that a similar level of energy & effort was required to generate it regardless of the tool chosen to perform the task.

[Dickie]

Citreon can correct me if I'm wrong, but what I think he was trying to say is that there are to many variables which contribute but can not be measured.

For instance in rowing, the seat travels up an incline, it take power to push ones bodyweight up that incline, but is that effort measured? Even if it is part of the calculation C2 uses, there is no scale on the seat and surely it takes more power to raise a 500 pound body versus a 100 pounder, but that difference is not accounted for, so a truly accurate Watts number can not be achieved. Likewise on a Bike there is no scale and it takes more power for a 300 pound person to climb a hill than a 100 pounder, how is that accounted for, and it gets worse when the grade of the climb increases, and on the downhill, while you have not slowed your cadence, you are not putting much force into the stroke as you would in a climb and force is part of the power calculation, is it accounted for on your bike? Is there a scale attached to your pedal measuring the amount of force in your stroke. A Watt is a Watt is a Watt, but how various companies measure that Watt differs.

So, the manufacturers of these measuring devices do the best they can with what they know, but they probably do it in different ways. So you can not compare the different pieces of exercise equipment.

At least with the rower, there is no headwind or tailwind and there are no hills, so you can compare the watts output from one row to another on the same machine. I think the only time you could say the same thing for a bike would be comparing rides on a track or over the same route on the road.

Fred Dickie

[chris5150]

Nope still have to differ, power on a bike is the force going through the crank, it does not matter if your going up hill/downhill etc, speed is irrelevant. Take it to its extreme, going down hill pedalling lightly will measure hardly any watts, despite the fact you are doing 40 mph, going up a steep incline at 6 mph up on the pedals may give 350 watts, to get that on the flat you need to pull a big gear and be going 25 mph etc...but it doesn't matter, the size of the rider doesn't matter, the power of the force at the crank is a watt, despite all the other outside influences, think of it like a torque wrench, regardless of the length of the handle & the size of the nut, a force of 300 newton metres ( or whatever they measure it in ) remains the same force, everbody needs to know how much to tighten their nuts, as it were!
So I know on bikes they use strain gauges to measure power, most are highly accurate, but what does the concept 2 rower use?.Surely force is force regardless of other influences. For eg if I was to squat 100kg then the watts I would need to do that would be a lot, lets say in this example 350 watts of leg power.I couldn't then replicate that level of wattage say with a dumbbell curl on my left arm, my arm alone would not be capable of producing 300 watts by itself.
I don't quite understand why it would be different for one watt meter manufacturer to another, I just would of thought that a watt of power is a watt of power and its irrelevant as to how that is produced, the measurement would be the same.
You don't get someone saying ' aye yes that's 12 foot long, but oh hang on we measure it slightly differently so we shall call it 14 ft'
As I mentioned previously on motor vehicles a kw or bhp produced is a standard measurement, doesn't matter what weight is in the car, what hill its going up, what the wind is doing, a bhp is still the output measure of the engine,with watts I would of expected a similar bodily output of energy would equate to a similar wattage produced on any piece of equipment.

I would of expected that if I am rowing and have a blast and bash out 1.45/500 , and my HR goes to say 165/170 & I am struggling, lets say that is showing 300 watts, then I would expect a similar exertion on my bike, say going up a steep longish hill up on the pedals, but in my experience, the steep hill on my bike will show 400 watts for what feels like the same level of exertion. So I seem to be able to generate and sustain higher wattages whilst cycling than rowing for the same exertion levels.

[c2jonw]

Chris5150, Here's some background information on how we measure power on the Indoor Rower:
http://www.atm.ox.ac.uk/rowing/physics. ... l#section4

C2JonW

[Bob S.]

The erg monitor shows only the work delivered to the wheel. There is a lot of work done on an erg, accelerating and decelerating your body back and forth on the slide, that does not show up on the monitor. There is an especially a large amount of unmeasured work done at high stroke rates and by heavy rowers. There is probably similar unmeasured work done while cycling (e.g.lifting your feet), but it is a lot less than the unmeasured work on an erg.

Bob S.

[Bob S.]

Addendum to my previous post. C2 takes into account the unmeasured work in the assignment of Calories, to the tune of 300Cal/hour.

Bob S.

[jamesg]

There are at least three major differences between Watts measured on a bike and on C2:

C2 is digital, while as noted above, bikes use strain gauges, which are analogue. Digital should have no error, while analogue has both linear and full scale error, typically 3% of full scale. So if full scale is 1000W, the error might be 30W. The bike also has to measure speeds (a strain gauge measures force only, not power), and there could be errors here too. Some sprinters are said to produce 2kW or more and will want to know it, so the full scale error could be even higher, because straingauges must not be overloaded. Bike Wattmeter users will be tempted to want the errors all on one side. Analogue readings can also drift with temperature etc:
http://en.wikipedia.org/wiki/Strain_gau ... mpensation

On the erg we pull 1/3 of the time, two legs at once with the work going though all the rest of our bones etc to the handle (not the feet), and the pull is not constant, so the peak power output during the pull is perhaps 4 or 5 times higher than the average on screen. So it will be limited by maximum sustainable and transmissible repeated force, not just CV capability. In cycling there will be variation too, but perhaps not so extreme and the work goes direct to the pedals, so the average can be nearer the peak repeatable force.

Third point is as said by Bob, we shunt up and down the rail, and that's not free of charge. The power loss is not included in the W reading, tho' it is in the kCals.

We can calculate how much power cyclists can generate during a steep climb, if we know the vertical distance traveled, their weight and the time taken. Next TdF will have a go, if TV data is enough.

[Citroen]

My point is that the equipment may gather identical data in identical ways (as discussed above it doesn't) but the muscles used, the sequence they are used in and the range of movement between a bike and a rower are as alike as apples & oranges.

[hjs]

The erg monitor shows only the work delivered to the wheel. There is a lot of work done on an erg, accelerating and decelerating your body back and forth on the slide, that does not show up on the monitor. There is an especially a large amount of unmeasured work done at high stroke rates and by heavy rowers. There is probably similar unmeasured work done while cycling (e.g.lifting your feet), but it is a lot less than the unmeasured work on an erg.

Bob S.

Modern bikes push and pull, so the whole motion gives energy. One of the reasons why cyclers get such high watt readings compared to ergs.

[steveroedde]

Maybe a silly question but using watts as a measurement of power, are they the same ratio's whatever the discipline?

I have an SRM power meter on my bike, and quite comfortably put out 250 watts on that for say a couple of hours, but yet my time for a half marathon on the rower of 1.23.10 was at an average of 212 watts.
Note also that on the pace calculator 300 watts is equal to 1.45/500...that's quite a pace, break 7 mins per 2k.
Also note brad wiggins can pull 460 watts for time trials which in rowing terms would be some ridiculous time of 1.31 or something per 500...hard to pull , let alone sustain for an hour.
So how does generating watts on a rower compare to watts generated on a bike?

Chris, I would like to address what I believe was your original question, bike vs erg Watts for those athletes who do both. This has come up on the C2 UK forum a few times. It seems that the majority of athletes put out fewer Watts on the erg at most distances (by perhaps 5-10%). The lower output at the wheel is because of the directional change and other "inefficiencies" inherent in rowing (as others have pointed out). That said, when one looks at world class power outputs, one finds that pp (to say 30 seconds) is proportionally higher on the bike than 5-6 minutes (not surprising given the race duration of a 2k rowing event). Over very long duration's (2h+), again the bike power becomes proportionally higher again. Few rowers train for 4-5h events but many cyclists do.

For some, (myself included) The watts are pretty similar across the 2 platforms. This is somewhat unusual. I do pretty equal amounts of training on the bike/erg/OTW. Last years numbers (taken from the erg result and the same time on cycling my power curve) were:
Time erg W bike W
15.5 sec 754 1060
1:27.5 522 .5 513
3:12.5 394.1 396
4:00 358 361
6:43 342.8 336
17:44.3 29.6 272
30:00 279.4 265
35:59 278.6 250
1:00:00 248 240
1:20:00 235 240
2:42:57 225.4 183

As for the accuracy issue, the +/- 1-2% observed comparing SRAM, Stages, Garmin Vector and Power Tap is close enough for government work and allows valid comparisons. Sorry that the table is a bit screwed up....formatting change with cut/copy.
Did this help?
Cheers, Steve

[RBFC]

Another difference, with mechanical device considerations set aside, is the physiological circumstances of rowing and cycling. Rowing causes bilateral compression of the thoracic cavity, with the increased intrathoracic pressure impeding venous return to the heart somewhat. This will vary depending upon body dimensions and morphology, as well as excursion of the rowing stroke. However, there is a cost to this effect. Also, unless climbing/riding very strenuously, cyclists can relax the musculature of the upper body and reduce their diaphragmatic workload. Perhaps physical differences in the actual performance of the movements can account for the wattage variations. I personally haven't rowed millions of meters (almost to my first million), so please accept these comments as an educated guess.

Lee