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Post by cottmiler Sat Nov 20, 2021 4:59 pm

I was pleased to that our forum is featured 4th on this list!

I have tried Total Immersion, UK Swim Forum and Slowtwitch in the past.


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Post by cottmiler Sun Nov 21, 2021 1:51 pm

Here is a super article from Slowtwitch by Dan Empfield in which  he emphasises that good swimming form can only be achieved by having real strength to do it.

I think I have not appreciated this properly and must do something about it!

Last edited by cottmiler on Sun Nov 21, 2021 3:29 pm; edited 1 time in total


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Post by Sprinter Mon Nov 22, 2021 12:38 am

The idea of "anchoring the pull" is completely wrong, and that for obvious reasons.
Quote from that article:

"I don't look at the swim stroke as an exercise in pushing water. When you consider what the best swimmers do, their "pulling surfaces" experience very little "slip" in the water. It's amost like climbing a rope, hand-over-hand. Once you "anchor" your hand onto the rope your job is to pull yourself up. Your hand doesn't move the rope. The rope stays put."

The reasoning why this is completely false is as follows.

The most fundamental law concerning the physics of swimming is
 The conservation of momentum

The body of the swimmer gains a momentum p1 through the pull (we ignore the legs here), and we have

 p1 = -p2

for the momentum p2 of the water (assuming that the water and the swimmer are still, and thus p1 + p2 = 0; the same considerations apply to the moving swimmer in still water, due to linearity).

If actually anything like an "anchor" could be created, that is, by magic suddenly the water becomes solid, then still the above doesn't change, unless the solid water connects to the walls (and/or the ground). That would be pretty amazing, but for ordinary mortal swimmers this doesn't apply --- swimming speed is not altered by the distance to the walls, assuming normal swimming, and thus say a distance of at least one meter to the walls.

So we arrive at the fundamental law of swimming, any stroke whatsoever: forward movement of the swimmer is only possible by pushing the water backward, and indeed the momentum of the swimmer is exactly equal to the momentum of the water pushed back. This is independent of how much water is "grasped" (whatever) --- even if the swimmer is magically able to convert say a block of 10cm of water into some solid, still momentum is conserved, and the equation p1 = -p2 is valid (it would only become invalid of that block of water would connect to the walls, that is, if momentum would be transferred to the walls).

Thus if the hand of a swimmer is "anchored", no force is created, and the swimmer does not move. End of story.

To explain that myth about the "anchor", let's go a bit more into the details. Let's consider a moving swimmer, and the momentum created by the hand movement. Let's assume that swimmer is perfectly streamlined (no resistance), and let's assume a swimming speed of 1 m/s (50m in 50s). So at the beginning, the hand has a negative speed of 1m/s relative to the water. As soon as the pull starts, the hand-speed increases, but as long as the speed is negative, the hand creates only resistance. To emphasise: at the beginning of the pull you only get slower, no forward momentum can be created. At some point the hand-speed becomes zero, that is, the hand moves with 1 m/s backwards. Zero momentum is now created. If the hand would be pulled out right now, then the whole movement would have only slowed down the swimming speed, with zero positive effect. The creation of forward momentum only starts once the hand-speed becomes positive, that is, the hand moves backwards faster than with 1 m/s. This is now exactly the phase where forward momentum is created. So the only productive phase of the pull is the final push of the hand.

This is of course exactly what sports scientists have measured. That myth about the non-moving hand was just created by taking photos of the movement around the time when the transition from negative to positive hand-speed happens (and that transition must happen!). So the illusion is created that the hand would not move water backwards. But of course the real movement, the propulsive part of the pull, just begins here. And that is (of course) what is measured. I heared once a presentation of a (proper) sports scientists about the physics of swimming, where that misconception was mentioned (caused by not considering the whole movement of the hand -- and, of course, by bad physics, the belief in magical forces which move the swimmer): the initial experiments were repeated, now capturing the whole movement, and then (of course) the propulsive part of the hand movement was "discovered".

An aspect here is perhaps that competitive swimmers move at around 2 m/s, and thus the transition from negative to positive hand-speed happens relatively late (except for extreme sprinting), creating that wrong impression.

There is actually indeed an important possibility of a local solidification of the water, namely when hitting the water very fast (think of jumping into the water from a great height, and thus with great speed -- water can become very hard here). As explained above, this only helps in the propulsive phase of the pull (with positive hand-speed), but there it is indeed very important to apply maximum acceleration NOW: this enables one to transfer more momentum to the water, but, to say it again, that only helps with positive hand-speed.

Swimming is very easy, once one understands that. There is zero magic involved. Action equals reaction, that's all what there is about propulsion.

The importance of the high elbow has nothing to do with any "ropes" etc, but it is just caused by biomechanics: only with the relatively high elbow can the swimmer exert a good pressure over a good distance, with the hand pushing backward as exactly as possible in the propulsive (late) phase of the pull, for a good distance.


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