Stretched Shock Cord & Time

[Slidewinder]

Gregsmith,
I don't agree with either of your points.

1) If a normally tensioned cord goes from say, 7 pounds at the catch to 8 pounds at the finish, and a lesser tensioned cord goes from 5 pounds at the catch to 6 pounds at the finish, the average of the former and the average of the latter are still in the same relationship. Throughout the stroke, the latter is going to take less force to stretch than the former.

2) If this were true you could fasten a strong elastic cord to the wall and pull on it all day long and never get tired.

[Slidewinder]

bloomp and hjs,
You are both using an extreme condition to support your argument - a shock cord so slack that the chain return is slow and sloppy. I agree that such a condition is no advantage.
But from the full elasticity of a new cord to the slack condition you describe, there is a range of elastic cord tension over which proper machine functionality will be maintained. Even if that range is just two or three pounds, it has a cumulative effect (equal to several hundred pounds over the course of a race). On a well used machine, the chain can still be returning normally, but some of the force that would have gone to stretching the cord is now going to the flywheel. If it is 2.5 % as estimated earlier by Gregsmith, then that translates to about 10 seconds in a 7 minute race. The winner can thank shock cord variation for the victory.

[Citroen]

It won't affect performance/times/results.

I should qualify that. It won't affect performance/times/results as measured by the performance monitor. I agree that slack cords won't tire you as a rower as quickly, they're not as hard to pull against as tight cords.

There's a machine in my gym where the cords are too tight (despite the fact I've complained about it). If I row that for half an hour I'll feel it later in the horribly stiff shoulders that it causes.

[hjs]

bloomp and hjs,
You are both using an extreme condition to support your argument - a shock cord so slack that the chain return is slow and sloppy. I agree that such a condition is no advantage.
But from the full elasticity of a new cord to the slack condition you describe, there is a range of elastic cord tension over which proper machine functionality will be maintained. Even if that range is just two or three pounds, it has a cumulative effect (equal to several hundred pounds over the course of a race). On a well used machine, the chain can still be returning normally, but some of the force that would have gone to stretching the cord is now going to the flywheel. If it is 2.5 % as estimated earlier by Gregsmith, then that translates to about 10 seconds in a 7 minute race. The winner can thank shock cord variation for the victory.

Slidewinder, it's not extreme, in gyms that simply happens.

During races though, it never happens, the cords are all new with littlw or no variantion.

The 10 seconds you are distribing is not something I have come accross at all. 10 seconds is a enormous gap and for me the difference between going 100% max and being 95% recovered in a minute. I think I have a lot more erging experience then you and I am talking about what I have come accross.

You also ignore the fact that not the cord tension itself during the stroke, but also during the recovery playes a role, I again now from experience that a slack cord slows you down.

[Slidewinder]

hjs,
There must be a better way to return the chain. If machines in gyms commonly have the shock cords improperly tensioned, then this is not just a maintenance problem, it's a design problem.
Maybe a weight driven mechanism could be designed to replace the shock cord. Then the pull and return force would be constant over the entire life of the machine - no more adjusting or replacing shock cords, no more complaints from guys like me about elastic cord tension affecting times.

[gregsmith01748]

Slidewinder,

I think you might have misinterpreted my post.

With regards to point #1, my point is that the difference in tension between machines is say, 7 versus 8 pounds at the point where the tension is measured, then if the average return force is less averaged over the stroke, then the difference would be reduced by the same factor. So instead of 1 lb difference in force, it might be, say 0.5 lbs. No doubt there is a difference, just that the difference may be lessened.

With regards to point #2: I wasn't trying to say that you get all the energy back, but that the amount of energy return reduces the difference between machines. What I said is that is reduced the aerobic workload because you have a force pulling you back the slide, and I still believe it is true. This is unlike in a boat, where the oar definitely does not pull back. Again, the point I am trying to make is that an erg with higher shock cord tension will both be harder to pull and will provide more of a boost back up the slide. A machine with lower tension will be easier to pull, but also provide less boost back up the slide.

[bloomp]

hjs,
There must be a better way to return the chain. If machines in gyms commonly have the shock cords improperly tensioned, then this is not just a maintenance problem, it's a design problem.
Maybe a weight driven mechanism could be designed to replace the shock cord. Then the pull and return force would be constant over the entire life of the machine - no more adjusting or replacing shock cords, no more complaints from guys like me about elastic cord tension affecting times.

What I'm perplexed about is why you care. You do not post your training here, you don't claim to race or try to post the fastest piece for your age group. If the people that are racing and trying to set records do not care, why should you? No machine will be perfect and I think everyone realizes that. But in your attempt to normalize for the small percentage difference that may or may not be from varying shock cord tensions, you neglect the dozens of other things that could make big differences at posting times/distances. What about small variations in altitude? Or the ambient temperature of the room? Or placing the erg on an uneven surface?

[Bob S.]

What I'm perplexed about is why you care. You do not post your training here, you don't claim to race or try to post the fastest piece for your age group. If the people that are racing and trying to set records do not care, why should you?

The answer to that is simple. It is just another excuse to put down Concept2.

Bob S.

[Carl Watts]

There is nothing wrong with the C2 design in this area. My Model C was purchased in 2000 and I have yet to even retention the cord let alone replace it.

If you look more closly there is a pully system so the cord is made longer, this reduces the variation in force required to stretch it from start to finish over the metre or so.

The cord really doesn't enter the equation and like Hjs stated it's one that is too slack thats the big problem and I have to agree, at 36spm mine is starting to get marginal in the speed it can recover the chain.

There are far more important factors influencing your time than the cord, it's at the bottom of the list.

[gregsmith01748]

I can't speak for Slidewinder, but I'll tell you why I care. I'm curious.

My experience has been that between the dozen or so machines that I have used, I have never discerned a difference in my performance, but from an academic perspective, there seems to be a reasonable logic chain that return force variations could be large enough to effect things and I explored it because I thought it might help me understand the physics of the machine better.

I am a huge fan of the my C2 erg and a shameless promoter of the products. I resent that my curiosity is misconstrued as a put down to Concept2. Any rowing machine will have to have some method to pull back the chain/cable/oar and how that effects atheletic performance is, I think, a legitimate concern.

In the replies to this thread I have seen people say it doesn't matter, but I haven't seen (and I have been hoping to) a post that tells me what was wrong in the analysis that I did in my post. I really want to be wrong.

[Carl Watts]

What's more of a concern than the cord to me is why my 500M is so much faster on a Model D than my Model C.

Most people tell me there is no difference but the numbers on the monitor tell me otherwise, and we are talking seconds here not tenths of a second.

Perhaps my cord doesn't have enough tension after all !

[Slidewinder]

If people that are racing and trying to set records do not care, why should you?

I suspect the great majority of users, even serious users of the machine, are not aware of the impact variable cord tension has on times. If they knew, they would care.

I'm no rowing athlete. I'm a reasonably fit sixty one year old man. I have zero interest in comparing my erg scores with others. I do however, have an interest in things mechanical.

If cord tension variability affects times, and if machines in gyms commonly have cord tension out of adjustment, then these are real problems being discussed. It is not, as Bob S. wrote, an opportunity to take cheap shots at Concept 2.

[Carl Watts]

Thinking on this some more draws me to the conclusion that just doing some measurements on the cord itself isn't the whole story.

Your legs are obviously much better suited to a "Push" than a "Pull" so in fact by having a bit MORE cord tension may in fact be an advantage not a disadvantage. The stored energy in the cord can then assist in pulling you back during the recovery.

Perhaps someone here an expert on biomechanics could supply the relavent information but at a guess the available "Push" force available i.e for a leg press at the Gym or the drive on the Erg would be up to 10 times greater than a "Pull" or trying to say raise your leg with a weight on your feet.

I'm no expert with elastic either but if you had to put in 1.5 times the energy in you get back each stroke then a cord of the correct tension can offer a level of assist that is an advantage over one that is too loose.

In any case if you had a row of new machines at a competition, the differerence between them can be neglected, in fact you couldn't get a more level playing field in any other sport compared to indoor rowing.

[Slidewinder]

Carl Watts,
Of course elastic cord tension will help on the recovery, but this does not cancel the effort it takes to stretch it. I understand your point about the push and pull differences in the leg muscles, but could we then argue that a leg press weight-stack machine is easier with heavier weights because the weights help to return the legs to the starting position?

Maybe with new machines the playing field is acceptably level, but that condition is short lived. With use, variations in shock cord tension are inevitable. These variations will affect times. This cannot be reasonably disputed.

For those who still deny this, I would wager that the seed of doubt has nevertheless been planted. The next time any of us witness an indoor race and the difference between first and second place is less than five seconds, we will all wonder if the win was justified, or if it was the result of differences in shock cord tension.

[gregsmith01748]

You can exclude me from the "any of us" in your post. All major competitions are raced on brand spanking new machines, fresh out of the factory, and I'll wager that the shock cord tension is damn near identical for every machine.

If two competitors are within a second of each other over, maybe it has something to with the machine. Otherwise, it has a lot more to do with the person sitting on it, than the shock cord sitting inside it.