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.
by the time your toes get wet?
water is thick & heavy, some say it's viscous
our torsos aren't streamlined to slice the water like dolphins, our hands, forearms, feet & calves are limited blades that lack the surface area & shape to apply sufficent power to propel ourselves through it. Our muscles quickly tire.
Dear Quicksilver,
When I posted the 5 MPH at entry it was based on what I had been told. Turns out that is wrong. From the velocity meter, the speed of the body, when the hand first touches the water after the dive, is around 15 mph. Now you'll still have to guess how long it takes to lose 75% of that speed, even in the most streamlined position we can manage.
Gary Sr.
When I posted the 5 MPH at entry it was based on what I had been told. Turns out that is wrong. From the velocity meter, the speed of the body, when the hand first touches the water after the dive, is around 15 mph. Now you'll still have to guess how long it takes to lose 75% of that speed, even in the most streamlined position we can manage.
5 or 15 mph, it shouldn't matter: if your claim of 5 seconds to a dead stop is correct, then it should be about 2 seconds (from the time you hit the water).
If you've ever seen "the plunge" contested as an event you'll know that it takes much, much more time than five seconds to come to a dead stop. In fact, you'll also agree with Chris that velocity decreases aymptotically with time.
... 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).
...
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 have not seen the data you are looking at, so keep in mind that I'm floating a theory. You'll have to decide if it matches up with what you are seeing.
What you point out is still consistent with the power coming from middle or back part of the stroke.
A) The fastest point is when the hand first enters the water... That might be due to what the other hand is doing, which will be in the middle or back part of the stroke (depending if the person is more catch-up or more windmill).
B) The slowest point is when the hand is about at the shoulder... That implies that the swimmer is slowing down from hand entry to middle part of the stroke. This might suggest that the front part of the stroke is not where the power is. (At the very least, that position is not favorable for muscle leverage.)
What might be interesting is if you did the same swims with only one-arm and a pull-buoy (no kicking), to try to isolate what is happening during the stroke. It would be tough to make it close enough to a normal stroke (for comparison), but it would take some of the other variables (like the other arm pulling) out of the equation.
While Erik and Gary figure out where the propulsion comes from, anyone have any tips for measuring drag?
I am all about getting faster by doing less work.
Every week or so a thread will pop up talking about the benefits of a high elbow and vertical forearm. In theory (and practice, for those with great flexibilty), the longer you can maintain a high elbow, you can decrease oncoming drag forces and achieve better leverage during the stroke cycle.
I think front quadrant swimming is counter-intuitive to many of us old school swimmers who were taught to finish our strokes. The strongest propulsion always seemed to be generated as the hand is pushing water past your hip pocket.
That said, I enjoyed the article swimming on the freeway, and have tried to apply this to both back and free over the past year. It seems to be much more efficient than a rotary style stroke (for me anyway). I still find myself using a strong finish even though the arms are in more of a front quadrant cycle.
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).
I am not an engineer, but it seems to me that a swimmer's drag will approximately follow Stokes' Law; in particular, the drag force will depend linearly on velocity. In other words, doubling the speed will double the drag.
If that's the case, then an exponential loss of speed is the result and the time to lose 75% of the initial speed will be the same -- all other factors being equal -- regardless of what that initial speed is and regardless of whether you push or dive. (The absolute rate of speed loss will be greater for the dive, but the relative loss will be the same if the person is just as streamlined, etc.)
If, however, we are experiencing "quadratic drag," then the relative fall-off will indeed be faster with the dive than with the push.
I am not an engineer, but it seems to me that a swimmer's drag will approximately follow Stokes' Law; in particular, the drag force will depend linearly on velocity. In other words, doubling the speed will double the drag.
No, Stokes flow is for very low Reynolds numbers (ratio of inertial to viscous forces). A human swimming in water has a high Reynolds number (possible in the 10^6 range) therefore Stokes' Law does not apply. Drag definitely increases quadratically.
Dear Quicksilver,
When I posted the 5 MPH at entry it was based on what I had been told. Turns out that is wrong. From the velocity meter, the speed of the body, when the hand first touches the water after the dive, is around 15 mph. Now you'll still have to guess how long it takes to lose 75% of that speed, even in the most streamlined position we can manage.
Gary Sr.
