A while back, I jumped on the triathlon website Slowtwitch and got attacked for saying that the power in the freestyle pull comes in the front of the stroke (hand entry to shoulder), not in the middle (shoulder to belly button) or back (belly button to release). Nonsense...they said. Didn't you read the article by Popov's coach showing the power is at the end of the stroke?
That never made sense to me. After all, at the end of the stroke there is only about one muscle still working, the tricep, and the hand is not in that position for very long.
At last, I got the proof I needed. A few weeks ago I was tested on the Velocity Meter, a very cool device that measures the speed of the body through the entire stroke cycle. It was VERY revealing and provided tons of information I could not get elsewhere.
Such as:1) the body speed slows by as much as 40% from the fastest to the slowest point during a single arm stroke. 40%!!! That is huge. The difference in speed is directly caused by the body going from a relative streamlined position to a very non-streamlined position and back again.
2) The fastest point in the stroke cycle is when the hand first enters the water and the slowest point is when the hand is about at the shoulder underwater. That is when the upper arm is pointing nearly perpendicular to the line of the body (ie most drag).
I realize that the speed of the body at any given instant is a result of the propulsive power minus the drag forces, that one cannot determine just from the velocity that the power is really greater in front. But when the speed drops from 2.5 meters per second when the hand is in front to 1.4 meters per second when it is in the middle, I have to believe that the power in front is greatest.
By the way, the propulsive power of the arm is created by both lift forces at the beginning and drag forces in the middle, as the hand shifts from forward motion to backward motion (then forward again as it releases).
Anyway, read my latest blog on our website www.theraceclub.com to find out more revealing secrets from the Velocity Meter.
Gary Sr.
It ,too, is significant...especially if you pancake into the water.
Gary Sr.
Or worse, as some pancake "onto" the water.
I voted for the 1 second option, fwiw, just considering going from a dive and impacting the water, there's an immediate slowing.
A doctor, an architect and a professor walk into a bar...
and after they hit their heads, all 3 fall down. At what rate do they decelerate as their bodies in motion approach the ground?:D
What is very interesting is that positioning the arm straight down creates a larger drag coefficient than the arm positioned out to the side. That is why all great swimmers use high elbows....not for more power or surface area, but for decreased drag.
I have to say I never even thought of this. I always assumed it was for mechanical reasons. I wonder how a stroke would work where your upper arm stays above the water for the entire cycle? I'm assuming not well, otherwise people would use it, but why not? Is it a biomechanical problem or the fact that your hand needs to dig into the "good water" down deeper to produce enough force? I'll have to try this out sometime.
This is interesting stuff, Gary. It would be great to have full time access to a velocity meter to really test out some radical stroke changes.
From a pushoff my velocity went from a maximum of 2.9 m/sec to .6 m/sec in exactly five seconds, holding the tightest streamline my 58 year old body could manage. Not a dead stop....but pretty close. The 2.9 m/sec occurred just before the feet left the wall.
The deceleration is much greater on a dive because the initial speed is faster and there is more drag involved (which is very dependent on the entry).
Gary Sr.
...agree with Chris that velocity decreases aymptotically with time.
Spoken like true scientists and engineers. :)
Not to get off topic, but Myth Busters had an episode were they wanted to see if bullets would stop (or significantly decelerate) when fired into the water. They did. And in a matter of feet.
YouTube- Underwater Shooting - 01
The velocity curves I am referring to were with a pull buoy strapped on my ankles to take the leg propulsion out of the picture and isolate the pulling force.
The peak velocity and trough velocity are repeatable occurring each time in the same place with each arm. The power is definitely not coming from the back end as the hand is actually moving forward again (trying to get back to the front asap).
Few realize the imposing drag forces that apply as we change our arm position from overhead in front to angled down, peaking when the arm is perpendicular to the body line. The bullet analogy should tell you how significant drag forces are...and a bullet is relatively streamlined.
What complicates the analysis of power vs velocity is that most objects don't change shape while moving through a medium. The human body swimming does. It goes from relatively streamlined to very unstreamlined (a brick) and back to relatively streamlined in a matter of a half second or so. The drag is so imposing in this process that even our powerful arm pulling up front do not keep us from decelerating.
The most compelling argument for accepting that the power is in the front is that we spend half of our stroke cycle time in that position. The other half is spent recycling our arm to get back to that position again. Unfortunately the route back creates huge drag issues.
Finally, the race dive involves going from air to water, just like the bullet. At the interface, a third drag is introduced that doesn't exist on the underwater pushoff, called surface or wave drag. It ,too, is significant...especially if you pancake into the water.
Gary Sr.
The major contributor to drag (pressure drag) during the underwater pull is the upper part of our arm. That part of the arm is moving forward at all times, while the hand has a net zero velocity (forward at the beginning, backward, then forward again) and contributes little to forward drag.
What is very interesting is that positioning the arm straight down creates a larger drag coefficient than the arm positioned out to the side. That is why all great swimmers use high elbows....not for more power or surface area, but for decreased drag.
You can test this yourself by kicking 25 meters all out with fins, first with the arm positioned straight down (other arm in front) and then by bending the arm at 90 degrees to your side. Both contribute to a large drag (you will feel it!) but much more with the arm straight down.
IMHO it's no due directly to the straight down arm ... the straight down arm move the center of mass of the swimmer down, altering the balance, and reducing a little bit the natural level of buoyancy, in a word increasing the boby drag. i think that this one is the reason because you go faster with higher elbow and higher center of mass.
In real swimming the "mechanical" advantage of higher elbow is another (main) reason to use it Vs dropped elbow/straight down arm.
) The fastest point in the stroke cycle is when the hand first enters the water and the slowest point is when the hand is about at the shoulder underwater. That is when the upper arm is pointing nearly perpendicular to the line of the body (ie most drag).
Going to disagree with this -
That's not what my speed graph looked like when I did the test with Dr. G.
My speed during my right arm pull was pretty even - there was a small dip when my arm was in the middle of the stroke (shoulder) - but that was also precisely the moment my other arm entered the water and when I was not pulling straight back with the hand (small s). I don't think it's drag related - my arms are moving faster than my body - I don't think it can be drag.
My left arm is another story - but that's more of being ineffecient than anything else.
I have no problem matching Jason Lezak's turnover rate (about 34 strokes for 50 meters) in the last 50 meters of his record Olympic freestyle relay. However, not in my wildest swimming fantasy, do I approach either his distance per stroke or his time. (Well, maybe in this one fantasy involving....no,no)
If I am reading this correctly, you have it backwards: if you can match his per-50 stroke count, you have the same DPS as Lezak. But if -- as likely :) -- you don't match his time, then he has the same DPS as you but at a higher stroke rate.
And of course you are correct that speed will be a function of both DPS and stroke rate. I remember that Maglischo made a comment in his book (I don't have it here to check) that most of the swimmers at the elite level have very similar DPS but the difference between the first and last place was turnover.
