Improving Hill Descents By Observing With Your Skin

Hi folks,

There is an old expression, ‘seeing is believing.’ I would prefer to say, ‘observing is understanding,’ which comes from my life of learning to observe, as opposed to just looking. Because you have looked at something, which induced a pattern of activity in your retina, does not mean that you have observed anything of real meaning, which is a down-stream processing or brain activity that uses data derived from the retinal pattern. I worked for many years as a pathologist, training an increasing number of younger pathologists as I gained experience in my field. It takes time to become a skilled reader of tissue sections on a microscope slide because they are highly complex.

One trick that I taught all of my students was designed to take them from looking to observing. My method was simple but effective. I would instruct the student to sit at the microscope with a slide containing a tissue of choice, lung or brain or spleen, and ask them to select an interesting field of view using a 20x objective. This would result in an image that is ‘busy,’ but not too busy. As an analogy, imagine looking at a city from above but focus your attention on a few city blocks, not too much (the whole thing) and not too little (a single garbage can). I then instructed my students, be they pathologist or biochemist, to continually observe the section for ten minutes. This instruction would be met with sighs. After a minute of looking there would be shifting of feet, but then they would eventually proceed to exclaim, “Oh Boy! I didn’t notice that nuclear inclusion,” or some such observation. Then they would proceed to ‘notice’ more and more things that were there all the time. This is observation (or improved noticing).

Drawing what you see can also enhance the observing process, and it is the stock-in-trade of the teacher of histology (study of tissue structure). Try it yourself. Just look for ten whole minutes at a view of the countryside. New things appear that you didn’t notice at first, and these ‘new things,’ that were there all along, continue to appear for the full duration of the observation period. Draw it and you notice even more detail. This process is both revealing and tiring. Getting to know a person is the same, which is why you can’t have hundreds of real friends. It takes time for you to get to know each other. So looking and actually observing are not the same thing. Agreed? I was fortunate in that I experienced the process of observing liquid flow fields for many years, much like those shown in the video below. This YouTube video reveals the power of the unstirred boundary layer to hold dye injected into this region adjacent to the wall of the flow tank. It is this thin layer of stationary water that acts as an insulator of the wall. Dye or heat can only pass through this region by diffusion, unassisted by convective flow in the adjacent flow field.

The author enjoying his new bike on the long hill descent at the Lake Placid Ironman 2011

Then we come to hill descents on your bike. Once you reach a speed at which it is not possible to pedal, or such pedaling is not effective, your continued progress depends upon the momentum you achieved whilst pedaling plus the pull of gravity (a negative force when climbing). Your forward movement is impeded or you are slowed down by a number of opposing forces that resist your movement. Such forces include (1) tires interacting with the road, (2) stiff bearings, (3) brake pads dragging, and (4) air resistance. You can modify road resistance through optimization of tire design and pressure. A well designed and maintained bike will deal with numbers two and three, leaving number four, a complex area of study known to some as Boundary Layer Theory, with which I became intimately acquainted in my flow laboratory about 20 years ago. Please bear with me as I explain a simple experiment we carried out, for which the underlying idea came from a great colleague whom I haven’t seen for years, James Ultman.

I had a large flow tank containing water, within which I would study fluid flow in order to further my understanding of airflow patterns in the nose, where I was interested in the regional deposition of inhaled gases, notably formaldehyde. At that time I was struggling with the issue of linking the flow patterns in the tank with patterns of uptake of dissolved substances by the floor of the tank. I hypothesized that airflow patterns in the nose accounted for the precise distribution of lesions induced there by highly water-soluble inhaled toxic gases. Then Jim came to work with me for about six months as a visiting scientist, during which time we got to spend a lot of time doing research together. Jim, as an engineer, taught me a great deal. Then one weekend Jim phoned me at home to say that he had come up with an idea about the solution to our ‘deposition’ problem in the tank. The conversation went like this: “Kevin, why don’t you fill the tank with dilute photographic developer, and then place exposed x-ray film on the floor of the tank and where the boundary layer is thin (flow is directed towards the film surface causing more developer molecules to reach the film) you should see a darker spot because the developer will interact with (develop) the film more quickly in that location.” I thought, having been a photographer with my own dark room for about 10 years as a young adult, “Boy! That’s brilliant, especially the dilute bit, as it will slow down the process and make it experimentally manageable.” Otherwise the film would turn immediately black all over upon entering the tank. And back to work I went!

On arrival at the institute I went straight to the dark room to get a bottle of developer, which I diluted in a large bucket. Then I filled my 20 gallon flow tank with this solution of hydroquinone and other stuff, started the motor to initiate laminar (straight or undisturbed) flow through the tank, took a piece of x-ray film about 12″ x 12″ and placed it on the bottom of the tank with minimal disturbance, placed a random object (metal microtome chuck about 1.5″ square) on top of the center of the film to create a flow pattern or complex flow field downstream of the object, and then I watched and waited with bated breath.

In about 5 to 15 minutes (no idea how long exactly), I said, “Well, I’ll be damned.” The most remarkable pattern had emerged, and it exhibited extremely precise features, not the fuzzy smudge that I expected. In fact, I recognized the same sharp precision of exposed (developed) versus non-exposed film as that exhibited by formaldehyde-induced lesions in the nose (Guess we got that right! Only took about 10 years.). I was seeing the structure of the boundary layer through the mass transfer pattern (rate of transport of developer molecules to the film). In an instant I had a better understanding of the impact of a flow field on adjacent solid structures. Of course, the next thing I did was call Jim to tell him that his idea had worked better than I could have imagined, and this research was finally published in The Journal of Heat and Mass Transfer a couple of years later.

So the flow field structure interacts with the wall of the container in which the flow is occurring in an extremely precise manner. This is also true of you and the surrounding air during hill descents on your bike. You have to realize that you are in a large flow tank, and the flow field you generate as you rush along is interacting with you and the bike. Furthermore, if you stop to observe it, this interaction is sending you some useful information through the boundary layer all over your body.

And what is the use of all this physics mumbo-jumbo for me and my races, you may ask? The answer lies in the structure of the boundary layer around you and your bike. Wherever the boundary layer is thin, due to flow impacting or being driven towards the surface (your skin), there is resistance to your forward motion because energy is dissipated. Just sit up high on the saddle and you immediately slow down (I call this effect ‘air brakes,’ and they can save your butt on wet roads). Another thing you should notice is that you feel a cooling effect on the front of your body when you sit up, as the boundary layer of unstirred air is thinner due to air being forced against the front of your body. This has a cooling effect because the heat of your torso is more rapidly removed by the air due to thinning of the unstirred boundary layer (less insulation). Wetsuits keep you warm in cold water by thickening the boundary layer of unstirred water – same idea, same physics.

Now let’s take this a little further. As you descend in a tucked position, explore your body for cold spots (the colder the weather the better), and here is where you can improve your tuck or reduce drag by bringing in your elbows, modifying the angle of your spine on the bike, or whatever it takes to minimize areas of local cooling, which represent areas of flow resistance – or you can lay out a bunch of money and rent a wind tunnel. In fact, it would appear that you can have such an analysis on your bike for only $79.99, which surprised me.

That’s it. Sure wish I had that piece of film to show you, but it disappeared into the mists of time. You can always read the article if you want, but like all scientific articles today the excitement and wonder has been carefully extracted by the editorial process. I wonder how Jim is doing now, as I sure enjoyed working with him.

-k Your Medical Mind