Concept2 and lower back pain

johnlvs2run · Post by **johnlvs2run** » February 17th, 2010, 9:45 pm

Nosmo wrote:This design would fundamentally change the direction of force applied at the handle.

It would change to a fundamentally correct position, pulling from the water, vs pulling from the sky.

The change would become more like the on water stroke.

Currently it is like rowing on the water while keeping the oars up in the air.

It is a physical impossibility for any flexible object to transmit force in any other direction--it has to be in tension.

The axle is approximately 3 to 5 inches higher in relation to the railing than it was on the modelB.

Don't know if having the axle at rail level would be easier on your back or not (although I could easily see how it might encourage one to slouch)

Currently the body goes up and down in relation to the axle.
Would you be comfortable driving a car where the front seat went up and down several inches every couple of seconds?
No. The same thing on the rowing machine.

Having rowed more than 40 million meters mostly on a modelB, then C and D, I can verify the flat railing is most comfortable.

Greypuller · Post by **Greypuller** » February 18th, 2010, 12:12 pm

Interesting conversation.....either way, bottom line, it's a pretty good exercise and lower impact than many other types...thanks all!

Nosmo · Post by **Nosmo** » February 18th, 2010, 4:24 pm

John Rupp wrote:
Nosmo wrote:This design would fundamentally change the direction of force applied at the handle.
It would change to a fundamentally correct position, pulling from the water, vs pulling from the sky.

The change would become more like the on water stroke.

Currently it is like rowing on the water while keeping the oars up in the air.

On the water one pulls more or less straight back more or less level with the water, starting a bit lower then shoulder hight finishing at about one's sternum. This is the same as on the erg.

I do most of my rowing in a single or double scull. The direction of motion in a boat is very similar to that of the erg. (EDIT: originally said "Having the axle at rail level is not a big deal."---I did not mean this--it started as the rail slope is not a big deal but screwup up when erasing some sentences in the draft)

As for the angle of the rail, that is a separate issue and it just doesn't make much difference to me.

johnlvs2run · Post by **johnlvs2run** » February 18th, 2010, 5:01 pm

Nosmo wrote:On the water one pulls more or less straight back more or less level with the water, starting a bit lower then shoulder hight finishing at about one's sternum.

On the water, the line of force is from the shoulders to the water, in fact continuing below the water.

The line of force goes downward from the shoulders to the water. Also this is adjustable.

This is the same as on the erg.

It is not the same on the erg.

On the erg the line of force is almost directly forward to the axle, depending on the torso height of the person who is rowing.

The line of force is not the same as it is in a boat.

I do most of my rowing in a single or double scull.

You should be aware of this then.

Having the axle at rail level is not a big deal.

I am glad you agree.

As for the angle of the rail, that is a separate issue and it just doesn't make much difference to me.

It is not a separate issue.

Given a certain height of the axle, dipping the raining in front, increases the distance between a line from the top of the railing, to the axle.

The difference from the modelB to the modelCDE is caused by both of these things, (1) the axle is higher in relation to the ground,
and (2) the railing is dipped to the front, which further increases the distance between the line from the railing, and the axle.

snowleopard · Post by **snowleopard** » February 18th, 2010, 5:14 pm

John Rupp wrote:The line of force goes downward from the shoulders to the water.

Errrrrrr, if that were the case how does a boat move horizontally?

Nosmo · Post by **Nosmo** » February 18th, 2010, 6:56 pm

John Rupp wrote:....On the water, the line of force is from the shoulders to the water, in fact continuing below the water.

The line of force goes downward from the shoulders to the water. Also this is adjustable.
....
On the erg the line of force is almost directly forward to the axle, depending on the torso height of the person who is rowing.

The line of force is not the same as it is in a boat.

Sorry but in a boat force is applied more or less straight back as it is on the erg. It is applied TO THE OAR HANDLE more or less in a horizontal plane. If it was otherwise, the oar handle would change height. The oar acts as a level arm which translates that force to the water and hence the boat.

You are misunderstanding some basic physics. John, I'm not going to argue this any more. If someone else is unclear about what I'm saying then I'll try to clarify, but I don't see any possibility of convincing John otherwise. I don't like to invoke authority here, but I do have a Ph.D. in physics. Even experts get things wrong sometimes but this is not confusing.

John Rupp wrote:
Having the axle at rail level is not a big deal.
I am glad you agree.

That was an editing error (I erased only parts of two sentences instead of all of both)--did not mean to say that.

John Rupp wrote:
As for the angle of the rail, that is a separate issue and it just doesn't make much difference to me.
It is not a separate issue.
.....

Well you could look at it that way. Put some spacers under the front feet and make the axle level if you want. If you measure the axle height as perpendicular to the rail then, they are two separate design parameters that can quite easily be adjusted independently.

johnlvs2run · Post by **johnlvs2run** » February 18th, 2010, 8:58 pm

snowleopard wrote:Errrrrrr, if that were the case how does a boat move horizontally?

When the rower moves the line of force front to back, the boat goes the opposing direction.

johnlvs2run · Post by **johnlvs2run** » February 18th, 2010, 9:09 pm

Nosmo wrote:It is applied TO THE OAR HANDLE more or less in a horizontal plane.

Here is a photo showing the mechanics in a boat.

Notice the line from the shoulders to the water is not on a horizontal plane as you keep implying.

Nosmo wrote:Put some spacers under the front feet and make the axle level if you want.

Again you are totally misunderstanding the issue. However you raise or lower the feet, the angle between a line
from the railing and a line from the axle to the shoulders stays the same! It does not change by adjusting the height of the feet.

Nosmo · Post by **Nosmo** » February 18th, 2010, 9:21 pm

John Rupp wrote: Notice the line from the shoulders to the water is not on a horizontal plane as you keep implying.

They are pulling on the oar handles not the water! The force the hands apply is to the oar handles. The oar handles move in on a (more or less) horizontal plane, there for the force applies is in a horizontal plane just like an erg.

John Rupp wrote:Again you are totally misunderstanding the issue. However you raise or lower the feet, the angle between a line
from the railing and the distance to the axle stays the same! It does not change by adjusting the height of the feet.

Who said anything about the feet? My point was the just what you said, changing the slope of the rail doesn't change the distance to the axle. Therefore the height of the axle and the slope of the rail are separate issues. C2 could have chosen any slope and any axle height independent of each other.

This is getting really silly.

johnlvs2run · Post by **johnlvs2run** » February 18th, 2010, 9:31 pm

Nosmo wrote:They are pulling on the oar handles not the water! The force the hands apply is to the oar handles. The oar handles move in on a (more or less) horizontal plane, there for the force applies is in a horizontal plane just like an erg.

The line of force is from the shoulders to the water. Look at the photo!

Nosmo wrote:Who said anything about the feet.

You did.

Nosmo wrote:Put some spacers under the front feet

Nosmo wrote:My point was the just what you said, changing the slope of the rail doesn't change the distance to the axle.

By raising or lowering the feet -- which is what you suggested -- it makes no difference because that does not change the angle from the line of force to the railing.

It is the line of force that is too high, that needs to be changed, preferably to match the line of force from the shoulders to the water in a boat.
Regardless of that, it would be silly (your word) to have a horizontal line of force.
Why not put the cage up a couple feet higher and pull downward, if it really makes no difference as you keep suggesting.
Of course it makes a big difference.

johnlvs2run · Post by **johnlvs2run** » February 18th, 2010, 9:37 pm

Here is an example of a woman (Erin Cafaro ) in a boat.

Notice the angle of her shoulders, to her hands, to the water, and compare this to the level plane of the water.

johnlvs2run · Post by **johnlvs2run** » February 18th, 2010, 9:46 pm

Here is a woman rowing on a concept2 rowing machine.

The line of force IS horizontal here, due to (1) the dip of the railing and (2) the height of the axle.

This is totally different than the mechanics in a boat -- see previous two photos.

peterhowd · Post by **peterhowd** » February 18th, 2010, 10:22 pm

John - you are wrong about the forces for OTW. Nosmo is correct, for a good rower, a mostly horizontal force is applied by the acceleration vector described initially by the path of the hands. Acceleration is transmitted down the oar and force applied to the water by the blade of the oar. Since water is pretty much incompressible, a force in the opposite direction moves the boat forward. I think you are confusing the mechanical advantage that might be gained through tuning the angles in the mechanical system with the resulting force directions (or force vector magnitude with force vector direction, if you wish.) The angles and lever arms are adjustable through technique and rigging of the boat/oars. The direction of the force vector during the drive is controlled by the path followed by hands, assuming the oars are rigid. I know they deflect parallel to the long axis, not so much perpendicular to it except during the worst of crabs. I have a data point or two on that!

Nosmo · Post by **Nosmo** » February 18th, 2010, 10:27 pm

John Rupp wrote:You did.

OK, confusion over human feet vs erg feet.

John Rupp wrote:By raising or lowering the feet -- which is what you suggested -- it makes no difference because that does not change the angle from the line of force to the railing.

exactly we agree. This is why I said the slope and axle height were independent parameters. You are agreeing with me.

John Rupp wrote: It is the line of force that is too high, that needs to be changed, preferably to match the line of force from the shoulders to the water in a boat.

In a boat the oar handle moves in the direction that force is applied to it. This is a physical law. The handle does not move in the plane defined by the line between the shoulders and the arms. Look at the hand position of someone rowing. Ideally the chain should be on a line defined by the changing hand position. That is the direction that someone is applying force to the handle. There are slight deviations from a straight line during the stroke but that direction is what matters.

Erin Cafaro is on the recovery and has the blade out of the water, her hands will raise when she puts the blade in the water. Her hands will remain at almost the same throughout the drive. If she was not pulling straight back the blade level would vary during the stroke. (it does vary some what which is why I keep saying "more or less horizontal").

The perspective of the second photo distorts things too much. Better to look at the technique video: http://www.concept2.com/us/training/technique.asp
Compare to the video of MVB's rowing here: http://rowskills.com/testimonials.html
In both cases the hands move more or less horizontally. On the erg, the angle of the chain barely changes through out the drive. Therefore she is pulling directly away from the flywheel. The axle is at the correct height. Those with significantly different body size would be slightly less efficient, but for small angles the effect is minor.

John Rupp wrote: Regardless of that, it would be silly (your word) to have a horizontal line of force. Why not put the cage up a couple feet higher and pull downward, if it really makes no difference as you keep suggesting.
Of course it makes a big difference.

I was not suggesting it makes no difference. I was saying a horizontal line is the correct one. Putting the axle significantly lower or higher then it is would be different from rowing a boat.

johnlvs2run · Post by **johnlvs2run** » February 19th, 2010, 1:31 am

peterhowd wrote:a mostly horizontal force is applied by the acceleration vector described initially by the path of the hands. Acceleration is transmitted down the oar and force applied to the water by the blade of the oar.

You are both describing the front and back motion, whereas I am describing the line of force from the shoulders to the water.
That the rower on both the erg and otw go forward and backward, and would regardless of the angles, is not the point.

shoulders & arms otw = shoulders & arms on the erg
water otw = axle on the erg

line of force otw = shoulders > hands > water
line of force erg = shoulders > hands > axle

line of force otw = downward from shoulders to water
line of force erg = HORIZONTAL >>> NOT THE SAME

Were the axle right on the line of the railing, your points about front and back motion would still be the same,
but the angle between the line of force from the shoulder to the axle compared to the line from the railing would be entirely different!!!

The line of force would be downward to the axle, as it is downward to the water otw, not horizontal as the erg is presently.