PDA

View Full Version : I-Pull and video perspective



LindsayNB
August 8th, 2008, 01:43 PM
Excuse me if this message is a little long, I'm trying to gather my thoughts to write something up on video analysis and stroke mechanics. Eventually I hope to turn it into something worth writing up or putting into a video, but for now I'd like feedback on whether I've got anything basic wrong.

I was looking for a good video that exemplified the I-pull, as distinguished from the S-pull and found this underwater front view video of Thorpe:

http://www.youtube.com/watch?v=batQnvqsZy4

It seems to me to be a decent example of an I-pull in that if you watch the hands they move in a fairly straight line backwards, at least until they start the exit. There is some vertical movement, which is geometrically inevitable, but very little side to side movement, which is what the S-pull is all about. It is easier to see on his left arm (on the right side of the video) as he grabs some air with his right hand which is then shed part way through the pull, making it harder to see.

It seems to me that the head on front view should be the best view for judging arm position in that a view along the axis of travel means that you directly see the area that is perpendicular to the direction of travel, which is the prime determinant of amount of drag generated and therefore the force that can be applied in moving past the anchored hand/forearm. If the hand/forearm project to a long line in the image then you will maximize area and minimize slip, if they project to a short line, as they will if your elbow is leading your wrist, the area is smaller and you will slip more. If your forearm is pointing at the camera (as in dog paddle or streamlining) it has minimal area, and minimal propelling ability, but also minimum drag during streamline.

One thing that you note pretty quickly is that Thorpe's forearms are not vertical, he maximizes the areas used for pulling/anchoring by moving his elbows out to the side more than by pointing his hands down.

The side view can also be informative, especially if paired with the front view, in that it can indicate the cause of a less than maximized area seen in the front view, but it can also be misleading because it only indicates the effective length of the arm in the vertical direction. A forearm that is parallel to the bottom of the pool, and therefore in line with a side-view line of sight, appears to contribute little when in fact from the front it can be seen to contributing a large area. This can lead the observer to place an emphasis on a vertical arm position when a horizontal, or more likely diagonal, arm position is just as effective and may not require stressful contortions of the shoulder and elbow joints. Although side shots of Thorpe and Hackett often give the illusion of a vertical forearm due to perspective effects, front shots clearly show that their arm position is diagonal.

For an illustration of the danger of the term vertical forearm simply extend your arm straight up above your head, now in a relaxed fashion let the elbow flop to a ninety degree bend, you will likely find that your forearm is now horizontal but extending across your body above your head. Keeping your shoulder and upper arm stationary slowly rotate you arm so that your forearm is rotating toward a position where your hand is pointing straight ahead, the position it would be if you were horizontal in the water and your forearm was truly vertical. Don't force it!!! As you rotate you will likely feel your shoulder and the surrounding muscles tightening up well before you get to "vertical" and attempting to put your arm in this position is very liable to give you shoulder problems. This is why most swimmers intuitively resist the arm over a barrel metaphor and often revert to a straight arm pull - or at least what can look like a straight arm pull when viewed from the side.

Now, again extend your arm and hand to a position straight above your head but this time bring your hand down in a straight line a small distance in front of your body with your elbow hanging limp below it, i.e. your forearm will be vertical if you are sitting or standing while doing this. This is the extreme form of a "dropped elbow". Viewed from directly above your hand and forearm will occupy the minimim possible area with your forearm basically hidden behind your hand. The only thing providing any pull is the back of your upper arm. This requires the least effort and provides the least propulsion/anchoring. When swimmers think in terms of pulling water backwards instead of pulling themselves past an anchored arm a dropped elbow is very likely, we naturally lead with the forearm when pulling our hand back toward our core from an overhead or in front of the body position.

Now, one last time, extend your arm above your head and bring your hand down in a straight line, but this time concentrate on moving your elbow as far out to the side as you can while keeping your hand moving in a straight line down. Keep your shoulder muscles relaxed, as you move your elbow out you should feel some tension in your lat, the large muscle on your side under your arm, but not in the shoulder joint or muscles.

http://www.exrx.net/Muscles/LatissimusDorsi.html

As a further experiment stand or sit with your arm extended straight out to the side and resting on an immovable object or a wall, place your other hand on the lat muscle under your extended arm and then press down with the extended arm. You should immediately feel the lat muscle tense up hard.

Now turn so that your arm is extended directly in front of you and again press down, you should feel much less contraction in your lats, the force is mostly coming from the much smaller shoulder muscles.

This illustrates how arm position affects which muscles are used. By rolling your body and using a wide elbow during the pull you'll be using large muscles like your lats rather than smaller muscles in your shoulders which aren't as strong and tire faster.

In summary, when teaching the freestyle pull, the swimmer should not try to achieve a literal vertical forearm, the goal should be to get the elbow out to the side so that the forearm is perpendicular to the direction of travel, which will give the largest area to press against and the least amount of slip, as well as engaging the large lat muscles. It is useful for the swimmer to be able to actually experience the effect of different movements out of the water where they can be isolated and the swimmer can most easily understand concepts like dropped elbows. When doing video analysis it is necessary to consider the perspective effects in different views, every view has limitations and the potential to be misleading. The front view gives the most direct information on the critical issue of presenting maximum area to the water to minimize slipping during the pull.

JMiller
August 8th, 2008, 03:40 PM
That's right, EVF = EDF
http://forums.usms.org/showthread.php?t=9092&page=4


Eventually I hope to turn it into something worth writing up or putting into a video.

geochuck
August 8th, 2008, 03:55 PM
Every swimmer is not identical in body structure. Body is different, longer arms completely different stroke. You do not have the same body your stroke will be different. It still is not monkey see, monkey do.

LindsayNB
August 8th, 2008, 04:36 PM
Every swimmer is not identical in body structure. Body is different, longer arms completely different stroke. You do not have the same body your stroke will be different. It still is not monkey see, monkey do.

I agree entirely, my idea is not to come up with the one perfect stroke that will be perfect for everyone under every circumstance. For me it is about starting with general principles, once a swimmer has the basics down you can start to tweak and customize for the individual.

A lot of adult learners want things to make sense rather than just be told do it such and such a way. If I know why I am supposed to do something one way I can say, well, my shoulder won't let me do it just like that but I can get most of the benefit if I do it this way.

I found the Jonty Skinner article on the effect of SCY racing on technique interesting because he observed that coaches everywhere tell their swimmers to do it one way, and very few swimmers actually do it that way.

I also frequently think of the lift/drag debate and how totally wrong the lift folks were, and how easy it is to prove they were wrong, and how the swimmers just basically ignored them.

geochuck
August 8th, 2008, 06:31 PM
EVF = EDF

We don't need to confuse people EVF is eniough.

JMiller
August 9th, 2008, 11:52 PM
Right, keep it simple. Kick hard, move arms fast, and breath good.



We don't need to confuse people EVF is eniough.

geochuck
January 29th, 2009, 08:36 AM
Do you think we now have the "I" pull which seems to eliminate the "S" sroke because of increased body and shoulder roll??? Or do we get the results of the "S" stroke because of the body roll and shoulder and it now appears as the "I" stroke.

I wonder.

mj_mcgrath
January 30th, 2009, 09:33 AM
Grant Hackett uses that diagonal forearm as well:

http://www.youtube.com/watch?v=IwvtuHya40g&NR=1

but his hand doesn't seem to pass directly under his torso like Thorpe.
I suppose the closer your hand is to your body, the more power you can generate.--mjm