form question: overcompression

[atheist]

hello,

after finding out that my shins need to be vertical at the catch, i've realized that i slide too far forward at the catch, almost to the point of hitting my heels with the seat.

i've put some tape on the monorail to give me a slight bump at the right point, and am now rowing with a mirror to observe my form.

the only problem now is that my lower back is starting to hurt. i'm trying to keep everything straight, that is, bending from the hips.

is this a consequence of a new technique, or should i consider going back to the old way?

thanks,

steve

[jjpisano]

Steve:

I have the same question. I'm only 5 feet 9 inches tall and over reaching at the catch is one way for me to lengthen my stroke, though I know my legs are not in the strongest position possible. At some point, I'm going to make the transition but I'm not looking forward to it. In March, I did two workouts with a slightly shorter stroke and my ribs started to hurt. I quit after two workouts.

I was thinking if I were to make the transition, I could do distance work with a light stroke for a while. Then slowly increase the power on the stroke over time so that all the connecting parts get strengthened in a gradual manner.

I do have my doubts about the whole process, however. The Concept2 machine defintely rewards a long stroke - forward drive power on the chain is linearly forward throughout the stroke, unlike in a boat where the forward drive power is greatest in the middle part of the stroke and least at the beginning and end of the stroke arc.

In the end, however, a strong initial position probably trumps a few extra cms. of reach at the catch. To make that transition, I'll probably lighten up the stroke for awhile - get the new pattern ingrained, which may take some time (after all I've done 100's of thousands of strokes with the overreach) and then gradually strengthen the stroke.

[PaulS]

I do have my doubts about the whole process, however. The Concept2 machine defintely rewards a long stroke - forward drive power on the chain is linearly forward throughout the stroke, unlike in a boat where the forward drive power is greatest in the middle part of the stroke and least at the beginning and end of the stroke arc.

Please do not keep this myth going! While it may seem reasonable (on very casual inspection), it completely ignores what we know about hydrodynamic lift (WRT the blade/water interface) during the rowing stroke and the force profiles that work best to move boats.

Yes, I know Mike Spracklen continues to expound that point of view also (as recently as in the book Rowing Faster), but he is doing so to ensure that his rowers maintain pressure throughout the drive as best they can, not cause the greatest input when the blade is at the square-off position, as doing so would simply cause greater slip and not do much more than form an impressive puddle that did little to advance the system.

Every time this gets mentioned it's like fingernails on a chalkboard (which doesn't bother me, but I think works for illustrative purposes). it's right up there with "Boat Pinch".

[atheist]

Jim,

I'm even "only-er:" 5'6"!

I guess what I'm wondering about is whether to put the time in fixing the overcompression when it doesn't seem to be bothering me otherwise. I have no knee/hip issues, other than the normal approaching-40 yrs old stuff; indeed, I credit my rowing with keeping me as flexible as I am.

Also, I'm not sure exactly what is causing the back pain. My theory is that it's a result of actively trying to stop/brace myself at the catch. I wonder if having slides would make this easier. BTW, I'm on a model-B with a PM3.

-steve

[Hapa]

hello,

the only problem now is that my lower back is starting to hurt. i'm trying to keep everything straight, that is, bending from the hips.

is this a consequence of a new technique, or should i consider going back to the old way?

thanks,

steve

Could be due to the new technique. Make sure you're watching your body positioning on the drive as well, especially the initial portion. You want to make sure you're not either "shooting your butt" or "opening your back" too soon.

Shooting your butt is where your legs start the drive, butt moves back, but your shoulders don't follow. This would cause your body to compress down, then you'd have to catch up with your back to finish the stroke.

Opening your back too soon is where you leverage your back to swing your torso too soon in the drive so you're not utilizing your leg drive to full effect.

Good luck with everything.
Aiko

[Nosmo]

Paul,
Please explain your understanding of what is ment by "boat pinch" and what is wrong with it. I thought that it simply ment that at the catch one component of the force is directed toward the center of the boat. Seems like simple high school physics.

Thanks
Nosmo

[PaulS]

Paul,
Please explain your understanding of what is ment by "boat pinch" and what is wrong with it. I thought that it simply ment that at the catch one component of the force is directed toward the center of the boat. Seems like simple high school physics.

Thanks
Nosmo

You've got the meaning correct as far as I can see. The problem is that though it is simple physics (the stuff that makes planes fly), the concept of hydrodynamic lift and it's applicability to rowing still eludes a vast number of folks in the rowing community right up to some very successful coaches. Though some seem to be catching on. (pun intended)

This site will give a relatively good explanation of why I refer to "boat pinch" as a myth.

While Mr. Atkins does not have a great deal of rowing experience (none, when I asked him about it a few years ago), his modelling of the rowing stroke is quite good. The questions I have are with some of the interpretations of the data and not so much with the data itself.

I'll put it this way, once the boat is under way and the system moving along the surface of the water. If one were to have some from of sensor on the pin, that would plot the direction of the force being applied to the pin, that force would be in the direction of travel and not at various angles off that line. If that were not the case, the force at the pin and foot stretchers would not balance and we would find it very hard to advance the system very quickly. Another bit of evidence for this is that the blade tip exits the water at a point closer to the finish line than it entered at the catch, meaning that even the relatively large slip (when the blade is "stalled" +/- 10deg off perpendicular to the hull centerline) does not negate that advance. The "lift" is always in just the direction that we need it to be to balance the opposite force being applied at the handles and subsequently transmitted to the pins. Since we can only drive our feet in a direction opposite of the hull travel, the balancing force has to be in the direction of travel, and there is even enough in favor of the direction of travel to accelerate the entire system and get us where we want to go.

[Nosmo]

I'll put it this way, once the boat is under way and the system moving along the surface of the water. If one were to have some from of sensor on the pin, that would plot the direction of the force being applied to the pin, that force would be in the direction of travel and not at various angles off that line. If that were not the case, the force at the pin and foot stretchers would not balance and we would find it very hard to advance the system very quickly. Another bit of evidence for this is that the blade tip exits the water at a point closer to the finish line than it entered at the catch, meaning that even the relatively large slip (when the blade is "stalled" +/- 10deg off perpendicular to the hull centerline) does not negate that advance. The "lift" is always in just the direction that we need it to be to balance the opposite force being applied at the handles and subsequently transmitted to the pins. Since we can only drive our feet in a direction opposite of the hull travel, the balancing force has to be in the direction of travel, and there is even enough in favor of the direction of travel to accelerate the entire system and get us where we want to go.

I'm going to have to think about this some more but I see nothing in the link that contridicts the idea of pinching, just that boats are fastest when the pinching is not symetrical at the catch and the finish. (I can think of a few reasons for this)

Looks to me like the force perpindicular to the direction of travel at the oar blade is balanced by the opposite force at the pin (not at the handle or the streechers).

You may be right but I don't see it off hand (and I do have a Ph.D. in physics). Thanks for the link and the response. There is a lot to think about.
Nosmo.

[PaulS]

I'll put it this way, once the boat is under way and the system moving along the surface of the water. If one were to have some from of sensor on the pin, that would plot the direction of the force being applied to the pin, that force would be in the direction of travel and not at various angles off that line. If that were not the case, the force at the pin and foot stretchers would not balance and we would find it very hard to advance the system very quickly. Another bit of evidence for this is that the blade tip exits the water at a point closer to the finish line than it entered at the catch, meaning that even the relatively large slip (when the blade is "stalled" +/- 10deg off perpendicular to the hull centerline) does not negate that advance. The "lift" is always in just the direction that we need it to be to balance the opposite force being applied at the handles and subsequently transmitted to the pins. Since we can only drive our feet in a direction opposite of the hull travel, the balancing force has to be in the direction of travel, and there is even enough in favor of the direction of travel to accelerate the entire system and get us where we want to go.

I'm going to have to think about this some more but I see nothing in the link that contridicts the idea of pinching, just that boats are fastest when the pinching is not symetrical at the catch and the finish. (I can think of a few reasons for this)

Looks to me like the force perpindicular to the direction of travel at the oar blade is balanced by the opposite force at the pin (not at the handle or the streechers).

You may be right but I don't see it off hand (and I do have a Ph.D. in physics). Thanks for the link and the response. There is a lot to think about.
Nosmo.

Perhaps you are not approaching it as simply as I have seen in the past.

For example, "boat pinch" would entail force vector toward the boat at the pin, and while it looks as if the outward moving blade would require just that, it is not the case with a boat under way.

I probably should have asked in return, what you think "boat pinch" is.

I agree completely that the pressure that is balancing against the foot stretcher force is at the Pin, the blade and handle forces vary by some ratio, that I'm sure you would be able to define far better than I. (Say, taking a nominal inboard and outboard of 88cm/210cm.)

Actually, with your expertise, do you see a way that the hull distance travelled during the drive could be calculated from the oar inboard/outboard and arc length?

[becz]

I'll put it this way, once the boat is under way and the system moving along the surface of the water. If one were to have some from of sensor on the pin, that would plot the direction of the force being applied to the pin, that force would be in the direction of travel and not at various angles off that line. If that were not the case, the force at the pin and foot stretchers would not balance and we would find it very hard to advance the system very quickly. Another bit of evidence for this is that the blade tip exits the water at a point closer to the finish line than it entered at the catch, meaning that even the relatively large slip (when the blade is "stalled" +/- 10deg off perpendicular to the hull centerline) does not negate that advance. The "lift" is always in just the direction that we need it to be to balance the opposite force being applied at the handles and subsequently transmitted to the pins. Since we can only drive our feet in a direction opposite of the hull travel, the balancing force has to be in the direction of travel, and there is even enough in favor of the direction of travel to accelerate the entire system and get us where we want to go.

I'm going to have to think about this some more but I see nothing in the link that contridicts the idea of pinching, just that boats are fastest when the pinching is not symetrical at the catch and the finish. (I can think of a few reasons for this)

Looks to me like the force perpindicular to the direction of travel at the oar blade is balanced by the opposite force at the pin (not at the handle or the streechers).

You may be right but I don't see it off hand (and I do have a Ph.D. in physics). Thanks for the link and the response. There is a lot to think about.
Nosmo.

Perhaps you are not approaching it as simply as I have seen in the past.

For example, "boat pinch" would entail force vector toward the boat at the pin, and while it looks as if the outward moving blade would require just that, it is not the case with a boat under way.

I probably should have asked in return, what you think "boat pinch" is.

I agree completely that the pressure that is balancing against the foot stretcher force is at the Pin, the blade and handle forces vary by some ratio, that I'm sure you would be able to define far better than I. (Say, taking a nominal inboard and outboard of 88cm/210cm.)

Actually, with your expertise, do you see a way that the hull distance travelled during the drive could be calculated from the oar inboard/outboard and arc length?

I think there has to be some component of force perpendicular to the direction of travel (when the oars are not at right angles to the boat), and it is at the pin, but it is balanced by the equal and opposite forces on the port and starboard side. If you draw a free body diagram of the oar and pin only, something will have to balance the perpendicular component of the force resulting from the pressure on the face of the oar.

When I've heard people talk about boat pinch before, usually it seemed to involve finding the most efficient position of the foot stretchers relative to the pin, so that at the point where the applied force is the greatest (at the start of the drive) you get as much propulsion as possible, realizing there will have to be some component of force perpendicular to the direction of travel.

For boat travel as a function of other parameters, I think it only depends on outboard and arclength. For a given outboard, you can change the inboard, but if you have the same arclength, the boat will still travel the same distance during the drive. The hands will just have to follow a longer or shorter arc, and the load will feel lighter or heavier depending on the change that was made. Any changes to arclength arising from a change in inboard would be more of a biomechanical thing (i.e. a function of a rower's arm length, flexibility, etc.). From the formula for a circular arc segment, I think the distance of travel will just be

outboard * sin(arc/2).

[Nosmo]

For example, "boat pinch" would entail force vector toward the boat at the pin, and while it looks as if the outward moving blade would require just that, it is not the case with a boat under way.

Essentially you are saying that the blade slips in one direction and not in the other. It may be small but it must exist.

Think of it this way: IF you had really long arms and/or a boat rigged in such a way that the oars entered the water with the shafts parallel to the boat, then at the catch all the force would be "pinching" the boat, and none would be propelling it foward. The pinching would decrease to zero when the blades are at 90 degrees. How the perpendicular force decreases is the real question. I see or no reason why it should be zero at a catch angle of say 30 degrees.
Do you know if it was ever measured or if the computer simulations output it?


....

I think there has to be some component of force perpendicular to the direction of travel (when the oars are not at right angles to the boat), and it is at the pin, but it is balanced by the equal and opposite forces on the port and starboard side....

This is exactly right. There are opposite perpendicular forces at each pin the "pinch" or "squeeze" the boat.

Actually, with your expertise, do you see a way that the hull distance travelled during the drive could be calculated from the oar inboard/outboard and arc length?

I am an experimentalist so naturally I think it would be best to measure it. One would need a sensor on the oar to determine when and the angle at which the blade entered and left the water and a distance sensor (which could just be from the propeller on a stroke coach.) Alternatively a fixed video camera and still water or where one knew the current could work well for a single stroke. For more strokes one would need a moving video camera and an accurate measurement of the camera speed.

To calculate it one needs to know both blade slip and lift** . To first order we can assume slip+lift is zero, then you have simple geometry: distance =outboard * cosine(theta_c) + outboard * cosine(180-theta_f).
Where theata_c is catch angle and theta_f is the finish angle (zero at the bow, 180 at the stern for both)
If you want to know more acurately then that, it becomes a difficult fluid dynamics modeling problem. Perhaps the models you linked to above, do this well but it is not trivial. It is of couse dependent on a number of things like boat speed, drag, and water temperature.


**lift on the blade is concept I am not satisfied is being applied correctly to rowing but that is another whole thread.

[PaulS]

For example, "boat pinch" would entail force vector toward the boat at the pin, and while it looks as if the outward moving blade would require just that, it is not the case with a boat under way.

Essentially you are saying that the blade slips in one direction and not in the other. It may be small but it must exist.

Think of it this way: IF you had really long arms and/or a boat rigged in such a way that the oars entered the water with the shafts parallel to the boat, then at the catch all the force would be "pinching" the boat, and none would be propelling it foward. The pinching would decrease to zero when the blades are at 90 degrees. How the perpendicular force decreases is the real question. I see or no reason why it should be zero at a catch angle of say 30 degrees.
Do you know if it was ever measured or if the computer simulations output it?

**lift on the blade is concept I am not satisfied is being applied correctly to rowing but that is another whole thread.

For a stationary boat, I have no problem with "pinch" or "squeeze" existing (as illustrated by your parallel catch angle, at which point there would be no Lift either, until the handles had a force acting on them), but once under way (the usual condition in rowing), the area surrounding the square off (perhaps +/- 10deg) the blade stalls (no flow from tip to root or otherwise) and necessarily slips, creating the turbulence seen as a white and washy puddle. If there is too much slip, the flow from root to tip will not be reestablished and the finish is mostly wasted, relying only on tossing a small mass of water backward to minimaly propel the system forward. The main resistance provided by the blade near the catch is not off the face of the blade, but off the back of the blade just as off the upper surface of a wing.

Since you are an experimentalist perhaps this would help.
This will require an Oar and a floating dock.
With your waterside hand holding the oarshaft at a point near the button (the pin), and your dockside hand being used to apply the handle force in the normal direction (pushing, in this case), stand at the edge of the dock and place the blade in the water at some acute catch angle.
Push with the dockside hand and you will be driven onto the dock (boat pinch).
Now, and it will take a few tries to coordinate this, walk along the edge of the dock and plant and push in the same manner, making sure to keep the "pin" hand travelling parallel to the dock edge, and instead of being driven onto the dock you will be pulled along the dock directly by the "pin" hand. It's quite a strange sensation frankly. There won't be nearly enough force to provide any flex to the oar shaft, but when in a boat there is and being able to catch and drive very quickly has the same effect as having a more acute catch angle that results in a longer drive impulse.

My favorite illustration of this is to get in a 2x and row with the two distinct techniques (Lift Vs Drag emphasis) while the "observer" sits and feels the difference, and also observes the speed difference from an objective source (Speedcoach or GPS). What they perceive to be the slower technique (sharper stern check) is invariably faster than the near checkless but sluggish drive with a peak pressure in the middle of the drive. For a real world example of this check out the M2x in either Athens or the 2003 WorldCup, the Italians have the Drag emphasis and the French use the Lift emphasis.

This may be as good a place as any to give your explanation of "lift" as it applies in rowing, we're onto it anyway. And I'm always looking for better ways to express it. The practice of it was clear to me from early on, but the explanation of it still remains a challenge to do clearly and concisely.

[grams]

Back to the original question about back pain: try keeping your abs tight. If you are over-relying on your back muscles they get overworked. Your body is a sausage and the casing needs to be tight all theway around.

grams

[atheist]

hey, back on topic!

thanks grams!

the other stuff was interesting, too!

-steve

[gregory.cook]

I've had problems with lower back pain that seems to be related to overreaching at the catch. I work at keeping my shoulders relaxed until after I start my drive instead of moving them forward for the couple of extra inches.