Tri Talk Triathlon Podcast, Episode 59

Compression sock research and dimpled aero bottles. It’s aerodynamics, speed and spandex. A podcast for superheroes and triathletes! Today on Tri Talk.

Welcome to Tri Talk your podcast source for triathlon tips, training, news and more. To the bulk of new listeners from Southern California and London, thanks for checking out the podcast. In Southern California, I’m getting excited for Ironman California just a few weeks away. You triathletes in San Diego have a great local coaching resource there in Jim Vance. In London, thanks for being the #1 Tri Talk demographic outside the US. My goal at Tri Talk is to help you swim, bike, and run faster, to meet your personal triathlon goals. Whether you are an elite or amateur triathlete, we cover sprint distance to Ironman distance. I’m your host, David Warden, and this is Tri Talk Episode 59.

Today on Tri Talk we are going to talk about specific data supporting compression socks. They were all the rage in Kona this year, and the image of Torbjorn Sindballe in his knee-high white compression socks running to a third-place podium finish certainly fueled even more interest. We’ll look at some studies on compression socks. Also, we know dimples help golf balls soar and even help aero wheels cut through the air, but what about dimples on water bottles? I was lucky enough to get some data tested by John Cobb on whether dimpled water bottles actually improved aerodynamics. Also, stick around later in the podcast to find out how you can get some incredible free one-on-one coaching.

Before we get onto the good stuff, I’d like to review some feedback from Episode 57 and 58. In my excitement from publishing that episode, I had billed it as possibly the best Tri Talk Episode ever. The feedback from you the listener was a resounding, “huh?”

From listener Phillip in the UK, he points out the difference between correlation and causation and observed the following:

“I just want to point out that a correlation does NOT imply a causation.  It might help to prove causation, but not on its own.  If A is correlated to B, it means just that – they are correlated.  It does not prove A caused B in itself. For example, if you want to find out what causes house fires, you could try correlating “fires trucks in operation” to “fires that happen in a year”, for 100 cities.  You’d find a positive correlation, but that does not prove that fire trucks cause fires.”

Phillip also pointed me to a site that through the process of correlation could link global warming, earthquakes, hurricanes, and other natural disasters as a direct effect of the shrinking numbers of Pirates since the 1800s. Since pirates are indeed in decline for the last 200 years, and since natural disasters are on the rise, they are technically correlated, but that does not imply one causes the other. The same judicious approach has to be applied to the correlation research that I’m trying to do. Although mathematically and scientifically we can’t firmly prove causation between triathlon performance and spending, age, height, weight, etc. if we can accept that there is likely causation as well as correlation, then there may be some benefit to the research.

William, a professor at Iowa State University wrote to point out that although this was a correlation exercise, the values may not be significant.


“Your R2 values are SO LOW that to me they are almost meaningless.  I really couldn’t tell you off the top of my head of whether an R2 of 0.05 even means ANYTHING AT ALL! I wouldn’t be surprised, however, if you had enough data, you would find much GREATER correlations by breaking the data down more. For example, you might find different correlations between experience and performance as a function of age.  You might find different correlations between performance and height or weight outside certain norms (e.g., outside 135-180 lbs for men) or in different age groups. But the bottom line is that in order to do that, you really need a ton of data to sort through!”

Both Phillip and William are correct in their observation, and it is important to me that if you are going to take the time to fill out this survey, that you understand its limitations. ut Buf you listen back in episode 58, I think I spent a good 3 minutes discussing all the flaws in this survey process. I hope that it never came across as a true scientific study, and that I used the term for what it really is: a survey for which I applied a correlation analysis. The only way we can get the most value out of this is to, as William pointed out, get more samples and break down the data even more to see if we can find greater correlations in more granular data comparisons. To do that, I need your help in getting thousands of surveys back, and you can do that by visiting and clicking on research. Thanks to the hundreds of you who have taken the 10 minutes to fill that survey out. Please keep them coming!

One thing I did learn from this episode is to avoid the superlatives. “Best episode ever” is something that a producer should never bestow on his own work, and it erodes credibility. Another reason why I am not a professional radio host.

One more comment that came in on the cycling to run faster topic in Episode 57. From long-time listener and two-time guest on Tri Talk, Dr. Bill Thompson of Florida State University wrote:

“I feel obligated to share my disappointment in your shallow comments regarding the book *Run Less Run Faster.* It is not so much your opinion, but the fact that you hadn’t read the book, that puzzles me. We, your listeners and supporters, have come to know you as meticulous and thorough. You are correct in that world class, elite athletes will probably not benefit from this (this being cycling to run faster). But as shocking and painful as it may seem, I don’t think the Kenyans are listening to your podcast!”

If I portrayed the topic of cycling to run faster as a review of the book Run Less, Run Faster, then I apologize. The interest surrounding the book was the reason I wanted to research the topic on my own. It was not intended as a review of the book, but rather an independent look at one of the many reasons how cycling could be used to run faster. Perhaps I should not have even mentioned the book title to avoid the confusion.

Let’s get onto the good stuff! I know I billed the compression socks topic as the lead on today’s itinerary, but I’m feeling more like starting with the dimpled water bottle story. You can imagine that I get lots of requests from manufacturers to review and talk about products on Tri Talk. They send me samples, they make claims, their product is the best in the world, on and on. One company notified me of a product they were interested in me talking about on the podcast, specifically a dimpled water bottle that they claimed was more aerodynamic that a standard water bottle. I gave them my standard reply, which was, “thanks, I typically don’t review products unless I know for sure they are a benefit, can you send me any data.” I didn’t hear back for a few weeks, but then one morning I received an e-mail from the company that included data. Not only data, but wind tunnel data on the product from John Cobb himself, possibly the leader in wind tunnel testing for cycling. I’ll give you those numbers in a minute, but first let’s review why dimples could make a difference in a water bottle.

Cylinders and spheres are very convenient and strong shapes when designing bicycle frames and components, but it turns out they are terribly un-aerodynamic. I know they look all smooth and round, how could the air not just flow right on by them? Part of what makes an object aerodynamic is the object’s ability to keep the air attached to the surface as long as possible. As soon as you have what is called flow separation from an object, drag increases. This is why deep rims and disk wheels are more aerodynamic, because the air stays on surface longer, and the flow separation takes place much further along the flow of that object. The same with those thick downtubes that almost all tri bikes have now. More surface area on certain parts of the frame mean less flow separation and improved aerodynamics.

It turns out that with a cylinder or sphere, that flow separation takes place very early as the air travels over the object. But, please dimples on that sphere, like a golf ball, and something changes. Those dimples increase turbulance, which normally you would want to eliminate in aerodynamic design. But this turbulence, or “dirty air” on a sphere has the effect that it actually speeds up the airflow and gives it more forward momentum. As a result, flow separation takes place much later in the flow over the sphere. Even though there is increased turbulence, the trade off is that the increased speeds in airflow has a net benefit on the aerodynamics of the sphere, and the air stays attached to the surface much longer.

It is also important to note this is why we don’t put dimples on just any shape or object for which we are trying to improve aerodynamics. If dimples improve aerodynamics on a ball, why don’t we dimple the wings of an airplane? Or make the bike frame itself dimpled? The reason is that those dimples increase turbulance, and on a wing or aerodynamically tapered bike frame, the flow separation is already fairly good. The net result of increasing turbulence on a shape that already has late flow separation is decreased aerodynamics, while the net aerodynamic result of turbulence on a sphere is positive, because the turbulence contributes towards delayed flow separation.

This is also why there are critics of the dimpled rim of the Zipp 404 wheel. That deep rim already has good flow separation, so why add the dimples and more turbulence? I don’t know, but it is hard to argue with the results of the wind tunnel test of the 404s. It’s possible that the rim is just shallow enough, and the dimples just shallow enough, that the combined result is improved aerodynamics on that wheel.

So, back to this particular product. In theory then, since a cylinder is such a similar shape to a true sphere, the dimples could actually help airflow over a water bottle. And with the typical water bottle much wider than the down tube and seat tube, it certainly sticks out like a sore thumb in the bikes total aerodynamic profile.

The data on this particular water bottle is quite surprising, and I would have been skeptical of it had I not seen John Cobb’s actual comments. He found that over a 40K time trial, the savings from this dimpled water bottle over a standard water bottle was 53 seconds. At a cost of only 19 cents per second saved, that is a very economical aerodynamic purchase, and if it were on the Tri Talk Top 20, the #2 most economical purchase you could make. From the test, most of that savings took place when the water bottle was placed on the downtube, as opposed to the seat tube.

Now, before you get too excited, remember that this was a 53 second savings over a conventional water bottle. The data I did not get was the baseline aerodynamics of the bike without any water bottle. Yes, the dimpled bottle was faster than the standard, but I would guess that it would be slower than no water bottle on the frame at all, depending on the frame, or the bottles mounted behind the seat.

Way back in Tri Talk episode 18, I talked about another water bottle study that John Cobb did, which found that a water bottle mounted on the downtube was in fact actually more aero than no bottle at all, with John Cobb speculating this was due to the air breaking around the down tube before it got to the seat tube. So, you might be saying that this means if a standard water bottle on a frame is good, than the dimpled much be better.

That test that John Cobb did was from 2003. Much has changed since then. It is hard to find a real tri bike now that does not have a true aero seat post. Very few tri seat posts and tubes are cylinders any more. In 2003, when the first tests were done, this was not the case. If your bike is a true tri bike with an aero down tube and seat tube and seat post, I would not place a water bottle on the frame. You are best with the aero drink up front and high mounted water bottles in the back. If it is a standard road bike that you have converted to a tri bike, and the seat and down tube are standard rounded cylinders, then yes, a dimpled water bottle seems to be the way to go. Or, if you are doing an Ironman, and you need lots of fluids with you, you may have to use the water bottles on the frame even on your tri bike, and then these dimples aero bottles would be a good idea.

The company that makes this product is Rocket Science Sports and you can check out their very inexpensive dimpled water bottle at

And I though I was going to spend just 2 minutes on that topic.

Moving on. You’ll remember that I am now affiliated with Joe Friel’s new company, TrainingBible coaching. I have two exciting announcements regarding the launch of this company. First, will be launching their own podcast which will include the current writing and research of Joe Friel. Plus, the podcast will include interviews with the experts from TrainingBible’s coaching staff. But best of all, it will be hosted by me! It’s like putting my voice on Joe Friel’s mind, it’s a thrilling combination. Look for the release of the TrainingBible podcast to release on February 23, just a few days from now.

Compression socks. They look cool, they feel pretty cool, and they are relatively inexpensive. But do they really work?


There are 3 proposed advantageous of compression socks. First, improving blood flow back to the heart during exercise. Second, preventing muscles from moving unnecessarily as with excess vibration meaning less fatigue. And third, speeding recovery through that same benefit of increased circulation.

Compression socks have actually been around and used for quite a long time. But they have been primarily used in the medical field for patients with circulatory problems. In fact if you do a Google search for “compression socks”, 90% of the hits will be for the medical use of compression socks. Therefore, almost all of the research has been done on less-then-fit subjects, and almost none of it has been done on actual athletes. Even the data that has been done is contradictory. Two primary studies from 2003 had conflicting results. One showed that the socks did not improve athletic ability, but most patients reported reduced swelling when wearing the socks. But, all of these subjects were suffering from thrombosis, or blood clots, to begin with. The other study from 2003 did show some improvement when wearing compression socks when walking, but the subjects in this test were again, patients, and the maximum speed that they walked as 1.5 miles per hour. Not athletic speed.

In short, there really is no research to support the athletic benefits of compressions socks on athletes, yet.

However, in terms of recovery, there is some good data. From just last year published in the Journal of Vascular Surgery, which I keep on my coffee table right next to Sports Illustrated, there was a study of 14 runners who performed 2 strenuous 10K time trials while wearing the compression socks, and another while not wearing them. 13 of the 14 runners who ran without the socks reported muscle soreness after the run, while only 2 of the 14 reported muscle soreness after the run when wearing the compression socks. That’s pretty good data to support recovery!

However, this same study noted no performance benefit in that 10K time trial. Since this is one of the only compressions sock studies done on athletes, so far the evidence for performance in athletes is neutral. There was no performance improvement when running a 10K with compression socks with these 14 athletes.

But for recovery purposes, almost all the studies support compression socks for recovery.


Here are a couple of other things to consider. Do compression socks really reduce vibration and therefore muscle fatigue? Many athletes claim that they do, but at least in this 10K study, there was no performance improvement. Also, I question the use of compression socks when performing regular endurance training. If they truly do limit muscle fatigue, are you limiting the amount of soft tissue strengthening by wearing them all the time? In the course of trying to reduce injury by wearing them for every run, are you simply conditioning the muscles to not tolerate race-level vibration and fatigue? Would you do all of your running year round on a cushy treadmill, and never subject your legs to the realities of running on the road? Would you stay on your trainer for every ride and never subject yourself to hills or wind? This argument is not bullet-proof because unlike wind, hills or running surface, you actually can control what you wear on race day. Technically you could train with compression socks 100% of the time race with them 100% of the time. But again, long term the effects to soft tissue strength and tolerance are suspect.

I suspect that the best use of compression socks would be during breakthrough workouts where intensity is high, like racing, and recovery takes longer. But for use during Zone 2-3 endurance running, when you might have 2 days to recover before the next run, that seems excessive. Just like taking supplements, just because a little is good, a lot is not better. Reserving compression sock use for intense workouts and racing, running on a recently recovered injury, or for after your workout during recovery, may give you all the benefits of racing and recovering with compression socks, without the risk of pampering your legs and soft tissue unnecessarily.

I suspect that in the coming months and years there will be much more research on compression clothing and this will have much more clarity. For now, I say get them and try them out. I’m actually wearing a pair of compression tights that I got for $32 at Walgreens in their pharmacy section, far cheaper than the full tights you can get online. But these do look kind of funny when you run. sells some killer black compression socks for $40 from Skins that look very cool when running. More expensive than the tights from Walgreens, but you look much faster. By the way, I learned a new term when researching this subject. You know that there is aerodynamics, and hydrodynamics, the study of the flow of air and water. There is also hemodynamics, the study of the flow of blood.

Finally, don’t forget that you can get access to all the old Tri Talk Episodes back to Episode 18. If you have not listened to all 59 episodes, your education is incomplete. Would you only watch Episode 4, 5, and 6 of Star Wars? Would you only read the last 3 books in the Harry Potter series? Of course not! Complete your Tri Talk collection today by visiting and access all the old episodes. See you next time!