My freestyle technique, what needs work?

Another old debate that this data sheds light on is the issue of accelerating through the pull. I suspect that most of us think of ourselves as swimming at a near constant velocity so that if we push back at constant velocity our hand will be traveling backward at a constant velocity. The data shows that the swimmer is actually varying between 1.5m/s and 2.25m/s for a range of 0.75m/s. That means that your hand has to also accelerate a like amount in the opposite direction just to maintain the same velocity and pressure on the water!

Thanks for the introspective analysis. It will take me a little while to work through this post, but I do appreciate the deep thought. Aha! As I and many others have long suspected, flutter kicking is not actually propulsive at regular swimming speeds! Toss those kick sets into the trash can! Well, probably not, but this would give serious weight to the argument that the kick is not used for propulsion but rather to maintain body position, or to set rhythm, or as a rotational anchor, or some combinationI think it is risky to try to segment just pulling or just kicking because during regular swimming, these are really integrated mechanisms. You could be pulling fine, and negate everything with a kicking pattern that creates a lot of drag. If you do swims using generally the same stroke frequency, and make significant changes in the kick, or any part of the stroke cycle, it is possible for our Velocity Meter to measure immediately whether it was a positive or negative change in the mean velocity. We actually recently tested a Master's swimmer that had a number of different permutations in technique that we tested and the telemetry was sensitive enough to show the differences/changes. Takes out all the guesswork and it lets the person visually see what they are doing. An important feature in making real changes. With the absolute amounts of drag and propulsion in the front quadrant not yet determined it is hazardous to draw too many conclusions but I think we can safely say that we're slowing down all the way through the front quadrant (except for the little bump) and we're speeding up all the way through the rear underwater quadrant. So you absolutely do not want to cut short the back quadrant in order to get your hand back in the front quadrant as quickly as possible, which was what was asserted in one of the other threads.In general terms, as the initial pulling phase begins, most are slowing down, (drag) but the amount can be minimized, once you see how much. (improving the mean swimming speed, or minimizing the max.-min. change in velocity. Again, from the measurements, it doesn't appear that even the max force values are very high. I actually have a very good example of this effect that I will post later. If we were able to overlay the Aquanex force data we would be able to separate out propulsive force from drag force and see whether it is lack of propulsion, or a surplus of drag that leads to the deceleration in the front quadrant. My hypothesis is that there is not a lot of propulsion in most of the front quadrant. The telemetry showed from when the hand enters, a progressive increase in force/pressure that for most peaks somewhere under the shoulder, in general terms. In contrast at the same time, the telemetry from the Velocity Meter clearly shows that instantaneous velocity is progressively decreasing to its minimum point somewhere under the shoulder.

Another old debate that this data sheds light on is the issue of accelerating through the pull. I suspect that most of us think of ourselves as swimming at a near constant velocity so that if we push back at constant velocity our hand will be traveling backward at a constant velocity. The data shows that the swimmer is actually varying between 1.5m/s and 2.25m/s for a range of 0.75m/s. That means that your hand has to also accelerate a like amount in the opposite direction just to maintain the same velocity and pressure on the water!We collect velocity telemetry at 1,000 data points a second to reveal all those variations in velocity, that the human eyes is not capable of sensing during a stroke cycle. Combined with the synchronized video we believe this currently is the best method of taking some of the guesswork/debate out of exactly when everything is really occurring from a velocity standpoint. The technology was developed and constantly improved over the last 25 years to help swimmers improve their performance, and give them an opportunity to view what they are doing, instead of trying to copy and visualize someone else. Every stroke cycle has velocity variations. The water is not a fixed object, that you can grab and absolutely hold onto, so maintaining a constant velocity is not possible.

I agree that there is still a good deal of mystery regarding the role of the kick. We know that the kick will cease to have any potential propulsive element when the forward speed of the swimmer reaches the maximum backward component of the foot velocity during the kick, and in reality long before that the drag will outweigh the propulsion. None the less, people do seem to pick up speed when they kick so any interesting theory has to explain that. It would be kind of funny if it turned out that people just move their arms faster when they move their legs faster. In general terms, as the initial pulling phase begins, most are slowing down, (drag) but the amount can be minimized, once you see how much. (improving the mean swimming speed, or minimizing the max.-min. change in velocity. Again, from the measurements, it doesn't appear that even the max force values are very high. I actually have a very good example of this effect that I will post later. The telemetry showed from when the hand enters, a progressive increase in force/pressure that for most peaks somewhere under the shoulder, in general terms. In contrast at the same time, the telemetry from the Velocity Meter clearly shows that instantaneous velocity is progressively decreasing to its minimum point somewhere under the shoulder. If the best way of going faster is reducing the amount that you slow down that makes a strong suggestion that prolonging the extension phase is going to be a poor strategy as you will be slowing down from the point the other arm stops being propulsive. This suggests that getting rid of any dead spot out front, if any, would be a good strategy. But I'm back into conjecture and there's a more pressing question to be addressed. If the force/pressure sensor shows a steady increase from hand entry to under the shoulder one needs to know the magnitude of that increase before going further because pressure increases with depth below the surface even before you start applying forces. Either you need two sensors, one on the front of the hand and one on the back, with the difference then giving you the actual force exerted by the hand, or you need to track and subtract out the pressure due to depth. Unless the pressures you are seeing make the depth pressure insignificant... Hmm, force per square centimeter at one meter below the surface would be the weight of 100 cubic cm, which is 100g. The total force over a 10 sq cm area, about the size of a finger, would be 1kg, so maybe roughly 8-10kg or 20 pounds on the area of a hand, which is up in the range of the forces you were measuring even before including the area of the forearm. It seems like depth pressure would indeed have to be accounted for in this sort of setup. Do you know if the Aquanex does this?

It seems like depth pressure would indeed have to be accounted for in this sort of setup. Do you know if the Aquanex does this? I am sure the Aquanex accounts for all of those parameters. Dr. Havriluk has published many peer reviewed papers, and has presented his findings at the best international symposiums for a very long time. I am confident in the peer review process all of those questions have already been asked and accounted for.

I am sure the Aquanex accounts for all of those parameters. Dr. Havriluk has published many peer reviewed papers, and has presented his findings at the best international symposiums for a very long time. I am confident in the peer review process all of those questions have already been asked and accounted for. After reading about the Aquanex on their website, and reading one of his studies I am fairly sure that he doesn't compensate for depth, and for his purposes he doesn't need to. He's looking at the shape of the force profile, and comparing average and peak values. I'll have to think about whether it's necessary for our purposes as well. Someone just sent me this link: with another swimming instrument: mobile.nytimes.com/article

I'll have to think about whether it's necessary for our purposes as well. Curious about your meaning of this statement?? I only meant that there might be a way to factor out the pressure depth qualitatively but I haven't thought of one yet. In his 2004 FINA paper the main purpose was to determine if increased force and increased velocity correlated. For the part where the same swimmer swam at different speeds the force due to depth pressure would be relatively constant so you can still say that the average pressure/force increases as velocity increases. I have to say that I am a little bit uncomfortable with fitting a quadratic curve to the data when all the data points fall beyond the range where there is significant curvature in the quadratic, it looks like you could have got as good a fit for a straight line. I'm also uncomfortable with labeling the y axis as force rather than pressure without an explanation. In the case we are dealing with the question is how much force is applied in the front quadrant, and since the velocity data only tells us the difference between propulsion and drag we don't know whether the deceleration is due to the drop in propulsion or due to increasing drag or a combination of both. The pressure sensor is telling us that force is increasing from hand entry to mid stroke, but unfortunately depth and exposed arm surface and resulting drag would both produce a rising value through the front quadrant. The easy way to test would be to gently lower the pressure sensor to the depth that it achieves during swimming and compare the magnitude and profile with what is registered while swimming. The pressure on the hand at 1m depth would be the equivalent of the weight of a column of water with a cross section the size of your hand, say 10cm by 20cm times a depth of 100cm is 20000g or 20kg or 44lbs. The peak value in the graph in the paper is 37lbs, but again, he doesn't explain how he gets from a pressure reading to a force, I guess he is using a surface area but he doesn't specify what that is so I can't compare. Until I can see the pressure/force profile for the sensor as it is lowered to a 1m depth it will be hard to interpret your data. The fact that the entire force in his paper can potentially be explained by depth makes me unsure of my assessment that the sensor doesn't measure a pressure differential rather than simple pressure. It seems like too big a factor to be left unexplained.

That ones seems to be a quantitative test. The velocity meter (with video) seems to be both qualitative and quantitative.

I am familiar with this device, and it's applications are very cool, but this technology is somewhat different from ours. The Velocity Meter/Video Technology is more of a "microscopic" view of swimming to identify where specific deficiencies in technique occur, or identify optimal technique relationships like stroke frequency/velocity, or to define optimal glide times/distances after starts/turns to regular swimming speed as two examples. The AvidaMetrics system looks like an excellent technology to track those values in daily practice sessions in kind of a "Race Analysis" format that collects valuable lap by lap information with large groups. In my opinion, technologies like this really compliment each other and give the coaches more of an objective view of their swimmers. I'll have to think about whether it's necessary for our purposes as well.Curious about your meaning of this statement??

: : : Pressure increases linearly with depth so as you move your hand deeper into the water the pressure on the palm of your hand will increase as your hand goes deeper and a pressure sensor on your palm will register increasing force. But the back of your hand is also going deeper and the force on it is also increasing. In this case the forces on the two sides of your hand cancel one another out and there is no net force, even though pressure on the palm is increasing. As you pull your hand backwards through the water you increase the force on the palm of your hand and decrease it on the back of your hand and that unbalances the forces and creates propulsion. : : : I don't believe that the depth will have anything to do with the force, rather it is the mechanics of the stroke that allow you to exert force on the water. Pressure increases with depth, but it increases on both sides of your hand. It is the difference in pressure that causes acceleration (the pressure gradient, in fluid mechanics), not the pressure. Otherwise, you could have an object with a special shape on one side and an ordinary shape on the other so that when you put it in the water it would accelerate. Objects don't, of course, rather they just sit there unless you push on them. You are right about the force balance -- the game is to increase propulsion and decrease drag to maximize speed in the water. I like Gary's idea of taping some streamers to your upper arms and then filming. That would show where the flow is going in an unexpected direction during your stroke. It is a very complex flow problem.