Rower is too hard to row

[JaapvanE]

"If it would affect times, which I highly doubt..." Many C2 rower users have reported on this forum a similar experience to the OP here, often complaining of a much greater machine to machine disparity. So you have their testimony, and their testimony is supported by the physics. They do not complain because of possible unfairness in competitions. They just want a rower with a PM readout they can depend on.

You BLINDLY ASSUME that the bungee is to blame. No measurement, no analysis, no explanation for John's results in his video. I know machines can feel different, but I'm not the type to enter wild speculations and blame a random part where there are literally dozens in there that can produce the exact same issue and basic mechanical engineering supports wear-in effects of all of them.

"You introduce a lot of complexity..." A lot of complexity by adding one sensor? That would make a total of two. I think 21st century technology can handle it.

An additional sensor, which more than doubles the failure rate. Tension sensors are afwful things to maintain (I talk ftom experience).

[Sakly]

And I have an opposite experience. A brand new machine in the gym feels a bit easier than my machine at home. My machine only has 3.5 million meter, so it is not really old. And other factors are, I use the gym machine on other times of the day, I have a different mood at that time, different fueling, different daily load of stress or whatever. So is it of interest? No. Does it give me a good workout anyway? Yes. Would I complain about it, if I would have to use my machine in a competition? Of course not, as I am aware of the different factors, which cannot be measured.

If I could have the possibility to try both machines side by side at the same time and get the exact same feeling, then I would try to go the route to find out the root cause, because then it is likely any part of the machine is giving the different feeling.

[Nomath]

...
I am not in a contractual obligation with anyone on this forum, so I am not required to do anything.

Sure!

...And as said, my alternative explanation is that the machine has to wear in. Given the low forces compared to the materials used, could take a couple of million meters though...

If I were a mechanical engineer, I would be very unhappy with your alternative explanation. It doesn't pinpoint any specific part of the machine and is therefore nearly impossible to validate. It does put in doubt the equivalence of C2 ergs, especially brand new ones, but also many that have been used for a year or two !

Thanks for the link to the quite interesting video : https://www.youtube.com/watch?v=15KT3efpeTQ
So now we have at least 3 real measurements as a start of a database of bungee cord tensions :
- my own erg (about 8M meters) : 1.2 kg near the catch - 2.2 kg near the finish - average 1.7 kg
- the old erg in the video (about 15M) : 1.4 kg near the catch - 2.2 kg near the finish - average 1.8 kg
- the brand new erg in the video (about 15K) : 1.8 kg near the catch - 5.1 kg near the finish - average 3.4 kg

It shows that my assumed difference in bungee tension of 1 kg between different ergs is realistic, not an overestimation.

The video demonstrates that the same person gets exactly the same time for a 100m sprint on the new erg as on the old erg. This seems to contradict the possible effect of the bungee tension. But note that the power in these sprints is very high. Rowing 100m in 17.6 sec implies 513 W average over the stroke. The stroke rate is about 45 spm. Assuming a drive:recovery ratio of 1.5:1.0 and drive distance of 1.5 m means the work in extending the bungee in the drive is about 17N x 1.5m/0.80s = 14W for the old erg. For the new erg about 28W.
In proportion, these numbers are significantly smaller than the 17W for extending the bungee in a 220W effort, the 2K of the topic poster. There the difference was 5 sec on a total of about 470 sec. It is clear that a smaller effect on a total of 17.6 sec is hard to measure precisely.

I won't discuss the drive:recovery ratio. It's too technical and it doesn't matter much. A different ratio leads to a different estimate of the possible loss if the bungee work is not regained in the recovery.

I would be pleased when the discussion is confined to the issue brought up by the topic poster.

[JaapvanE]

If I were a mechanical engineer, I would be very unhappy with your alternative explanation. It doesn't pinpoint any specific part of the machine and is therefore nearly impossible to validate. It does put in doubt the equivalence of C2 ergs, especially brand new ones, but also many that have been used for a year or two !

Its a fact of life when having some reasonable production tolerances and it is not a bad thing per se. Machines have to set after construction and modification (see for example https://www.marineinsight.com/main-engi ... l-engines/). There is no need to validate: you see efficiency go up (or friction go down) and plateau, then you're done. Often you can hear it as well (energy is often lost through noise) or see it through infrared camera's (energy lost via heat). From experience most manufacturers tell what the procedure is. Even cars used to have it (see https://en.m.wikipedia.org/wiki/Break-i ... al_run-in) ).

Machines designed to be identical never are to a full 100% due to production tolerances and history. Even high volume production lines (like car engines) have better and worse instances. When you look at the spread of failure rate of mechanical components under highly controlled circumstances (like high end mechanical platter harddisks used in a single hosting center), you still see a huge spread (thankfully).

How people use them, and maintain them, also affects the wear and tear of a machine. Does it get enough oil, is it used daily, is it neglected for long periods in a wet environment? C2 can design the machine to resist almost all abuse, but it will cost and it actually increases the run-in period (as materials are tougher...).

The video demonstrates that the same person gets exactly the same time for a 100m sprint on the new erg as on the old erg. This seems to contradict the possible effect of the bungee tension. But note that the power in these sprints is very high. Rowing 100m in 17.6 sec implies 513 W average over the stroke. The stroke rate is about 45 spm.

This is the power you'd expect to see in a normal race. Competitive rowers aren't too far off his 1:28/500m. If I recall correctly, Cam Buchan needed to break the 1.36/500m barrier on the 5K to qualify for British Rowing trials (sub-16 5K).

As said, there are a lot of things going on in a room. Sakly's comment also supports that. I notice my performance drops when I don't ventilate my room enough, as CO2 is increasing. And I use two fans, including a Wahoo Headwind. In my gym, fans are absent, and the door is way too small to ventilate decently, aside all these sweaty men around me puffing out CO2 as well. It might not be THE reason things are different, but it can change things.

The topic poster indicates there is a significant altitude difference between the machines. It has an effect on the human body, potentially making it feel heavier (my legs feel a lot heavier in the mountains, but I'm not a local). As Anu Dudhia suggests (see http://eodg.atm.ox.ac.uk/user/dudhia/ro ... #section14):

If oxygen uptake through the lungs is the limiting factor in aerobic power output, then you would expect your erg power scores to fall off at the same rate (or split times to increase by 1% for every 210 m due to the cube relationship between power and speed.

Please note, Anu Dushia is a physicist specialised in environmental studies (and a keen rower), and AFAIK, NOT an expert in the field of excercise physiology.

Mechanical differences, usage, maintenance, machine placement and storage conditions all differ across machines which aren't part of a single fleet. So they'll deviate and feel different. It is one of life's mysteries why.

[Nomath]

.....
Mechanical differences, usage, maintenance, machine placement and storage conditions all differ across machines which aren't part of a single fleet. So they'll deviate and feel different. It is one of life's mysteries why.

You are summing up all kinds of variables and, with more time, probably several pages could be filled.
I consider this as blowing up fog over the key question : how much of the elastic energy stored in the extended bungee cord is useful in the recovery ?

Think about the recovery as a sequence of motions. First you bring your arms forward. The elastic energy will help that movement. A high-tensioned bungee cord will make that easier. Next comes the forward motion of the body. It will also be helped by the energy stored in the cord. But about halfway the rail, you will have to brake the forward movement of your body by putting pressure on the footholds. Residual elastic energy will not help. It is like a cyclist with a tailwind who has to brake. The tailwind is no help but a nuisance. Or a cyclist on a downhill who needs to brake before a sharp turn. The downhill doesn't help. So roughly half of the elastic energy in the cord is lost! Definitely!

If you know the bungee tensions as a function of the drive distance, you can estimate the lost energy. And this will surely depend on the bungee tension.

[JaapvanE]

I consider this as blowing up fog over the key question : how much of the elastic energy stored in the extended bungee cord is useful in the recovery ?

I saw that discussion coming as well...

The key element here is "usefull". To be usefull energy stored in the bungee, it should save my body energy on the recovery: it should reduce the muscle power needed to return to the catch in a meaningful way. But I am one of those persons that rows strapless: I can only move forward by shifting my balance by pushing the handle and arms over my knees and closing the hips. I can't pull on my legs. Admitted, there might be a tiny fraction of force on the handle, but you are moving over 50% of the body mass of a human so such tiny force hardly has an effect.

Besides, friction in the bungy/chain system (sprockets, bearings) works both ways against you: in the drive it adds to the force to be overcome, but in the recovery it actually increases the resistance of the chain to return to the catch position.

When you look at high rate strokes, for example world records, you see that the chain actually loses its tension due to inertia: it flies up and down and typically forms a wave pattern. If the chain would be pulling on the rower significantly that wouldn't happen: it would be a straight line in the direction it is pulling the rower (i.e. a chain under tension). Essentially at high rates, you see that the return mechanism can hardly keep up with the chain returning. For example, look at this video: https://youtu.be/SVl0Zt-kZys , especially around 1:35 (a slo-mo). You see the chain bounce: that is a chain struggling to return to its catch position in time, not a rowing being pulled by it.

[Slidewinder]

You BLINDLY ASSUME that the bungee is to blame. No measurement, no analysis, no explanation for John's results in his video. I know machines can feel different, but I'm not the type to enter wild speculations and blame a random part where there are literally dozens in there that can

Analysis? Nomath's first post in this thread provides the analysis of what the OP has reported. I was going to post an almost identical breakdown, but Nomath's post made it unnecessary.

I am familiar with John Steventon's video. He made it while he and I were discussing this same subject elsewhere online. He made clear in our discussion, before he made the video, that he firmly believed in the equivalence of all C2 rowers. So may I suggest that he had a point to make and that his strong desire to make that point could have influenced the outcome. The PM display is right in front of him on each machine, and he got the result he wanted. Note that he does the 100 M on the new machine first then waits two minutes and gets on the old machine. He is fresher and stronger on the new machine - the machine with the stronger bungee cord. When he gets on the old machine he says, "definitely feels looser". He has just gone all out on the new machine and surely has some lingering fatigue after just a 2 minute rest break but it helps that the old machine is "looser" and so he manages to maintain the identical pace as on the first machine, and he hits the time he was aiming for. Then he reported back to me, using the video to support his argument that bungee cord strength makes no difference. Needless to say, I was not impressed or convinced.

[Slidewinder]

[]
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The video demonstrates that the same person gets exactly the same time for a 100m sprint on the new erg as on the old erg.

I am familiar with this video. To put it in context: John Steventon made it in response to a discussion he and I had on this subject. See my reply to JapvaanE about it.

[jamesg]

I can complete my workout with a 7:45 2,000 meter row. I can only row a 7:50 at home on my Model E. Even when fresh.

When fresh (ie cold)? This only confirms that warmup is a factor. I do the WODs which are mostly intervals, and the last few are faster and easier than the first, even if longer, since I don't do a real warmup before starting, only a 3 to 5 minute idle.

When racing, warmup is done by paddling down to the start and then doing a few 10-20 stroke starts, so can't be avoided. It's all to easy to miss that on the erg.

In any case, we are far more complex and less reliable than two bearings, a chain and a piece of rubber; so cannot use ourselves as benchmarks.

[JaapvanE]

So may I suggest that he had a point to make and that his strong desire to make that point could have influenced the outcome. The PM display is right in front of him on each machine, and he got the result he wanted.

So basically you question John's integrity? That is a common theme with you on this forum: everyone who disagrees with you is biassed. Then this is the end of the line with my discussion with you.

[JaapvanE]

In any case, we are far more complex and less reliable than two bearings, a chain and a piece of rubber; so cannot use ourselves as benchmarks.

I agree on the human repeatability part, although when people consistenly see the same results, I would say something is going on.

But the complexity bit definitely is true. It could be unmeasured environmental factors (air quality), or mechanical things that affect the quality of the catch for the OP that do the trick.

[Slidewinder]

So may I suggest that he had a point to make and that his strong desire to make that point could have influenced the outcome. The PM display is right in front of him on each machine, and he got the result he wanted.

So basically you question John's integrity? That is a common theme with you on this forum: everyone who disagrees with you is biassed. Then this is the end of the line with my discussion with you.

He told me he went all out on both machines. I replied that he could have unconsciously been influencing the outcome. He should have done the test blindfolded, with an assistant to call out when the target distance was reached. This would have eliminated any possibility of unconscious bias. He should also have done the test on each machine when fully rested. Instead, he did the new machine first and then got on the old machine 2 minutes later, so he would have already been slightly fatigued when he started on the old machine. That order, and his fatigue, would favour the belief he expressed to me before he did the test - that bungee cord strength makes no difference and does not affect the PM readout. Maybe he did go full out on both machines as he said, but given his strong belief in the equivalence of all C2 rowers, it is fair to ask: Was the test design (order of machine use; no blindfold; his inevitable fatigue before getting on the older machine) a deliberate attempt to game the outcome, or was it an unconscious manifestation of his bias? We don't know. I accept people as being honest unless proven otherwise so I will say that it was his unconscious bias. But the test is still tainted. You know that and so do I.

[stevegaspars]

I'm astounded that with all these arguments floating around the internet on drag factors, bungee cord tension and other obscure factors on rowing efficiency and speed that noone has made a chain yanker machine to put all these arguments to rest. Where's Jamie and Adam from Mythbusters?

[Slidewinder]

I'm astounded that with all these arguments floating around the internet on drag factors, bungee cord tension and other obscure factors on rowing efficiency and speed that noone has made a chain yanker machine to put all these arguments to rest. Where's Jamie and Adam from Mythbusters?

Researchers at the University of Ulm, Germany have built a 'chain yanker' machine. They have done some tests and have published a couple of papers. They plan to do more, and hopefully, will put many of these arguments to rest.

[Slidewinder]

Here is what I think is happening during the recovery with respect to the bungee cord:

The common argument is that the stretched cord assists the user on the recovery, and therefore a new, strong cord will provide more assistance on the recovery than an older, weaker cord, so the extra effort required on the drive is balanced out by the extra assistance on the recovery, with no net effect on the PM readout. The argument seems to make sense because there is some truth in it. Take an analogous situation: When you walk down a hill, gravity assists you, and if the hill is steeper, gravity will assist you more. But everyone knows that walking down a steep slope is more tiring than walking down a gentle one. Gravity wants to take you to the bottom faster than you want to go, so you have to exert effort, apply an opposing force to slow yourself down. Similarly, the stretched elastic cord wants to return you to the catch faster than you want to go. Release the handle from your grip and it will snap back to the start position more rapidly than any but the very fastest spm pace. When walking down a hill you can feel in your upper leg muscles the opposing force you must apply to slow yourself against the force of gravity. On the rower, during the recovery, the pressure you feel on your fingers is the force you are applying to the handle to slow its retraction speed. Yes, the elastic cord is assisting you on the recovery, just as gravity assists your downhill walk, but both require an opposing force.

So, although it is true that a strong cord will assist you more on the recovery than a weak one, it also means you will have to apply more rearward force to the handle to resist the greater speed and retraction force of the stronger cord. The stronger cord tires you more both coming and going. The only way to quantify this is with a force sensor, either at the handle or more conveniently at the termination point of the bungee cord. Then the tension profile of the cord through the entire stroke - catch, drive, and recovery - could be used to calculate user power associated with cord stretching and retraction, and the PM would then factor this power calculation, stroke by stroke, into the time/distance display. Equivalence between machines would then be ensured - or at least be much closer to the ideal of equivalence than what we have now.