DAVID SCHNAKENBERG: The Army has been using body composition estimates for a lot of reasons for many, many years. It is used most frequently on a cross-sectional basis, so I think what we realize now, in this era when we are trying to relate body composition to performance, is that it is critical for the technologies out there to detect change, in particular to detect change in the lean body mass, the muscle mass. If we feel somewhat comfortable from your earlier work, with a certain level of lean body mass loss you will have a loss of muscle strength.
So I think a promising technology would be one for assessing change in body composition in a relatively short period of time that could be used in the course of a field trial or where you are manipulating situations.
ROBERT NESHEIM: One of the things that occurred to me when Jim Vogel was talking about training injuries was that you could take a look at the body composition information and see whether you can get some predictability of
those people who are going to be most susceptible to certain training injuries. For example, if you could look at things such as bone mass, muscle mass, and some of these things, then perhaps this could be used to implement some sort of a training regimen that would strengthen those individuals predicted to be susceptible before they really get into the usual training program, which may cause these injuries. In other words, do some pretraining build-up of some of these conditions. I do not know whether this is a practical use for many of these techniques or not.
VERNON YOUNG: I would like to go back to Karl Friedl's interesting presentation and ask you to elaborate a little further on the change in the hydration of the lean body mass and whether you think this is extracellular, interstitial, or from another site. I ask this question as a follow-up to Doug Wilmore's area of concern, and because there is a lot of interest now in the role of cell volume in metabolic regulation and the role of the osmotic status of cells in gene transcription, even.
I think it is a really interesting observation, and we should not leave it at that. We should try to understand what it means from a mechanistic as well as a metabolic and functional point of view. Can you elaborate a little further, Karl?
KARL FRIEDL: Well, I agree it is interesting. I am not sure that we can elaborate too much over what we presented. It is there, and Ancel Keys never could explain why they had that. They had lower extremity swelling, so it seemed likely to be interstitial, at least certainly extracellular. We have Rangers that end up with a lot of these knee problems. Dr. Vogel showed you a slide of four pairs of knees that looked like examples of cellulitis, but some of those may be bursitis. They may even just be related to this hydration, and they may have gotten swollen knees from this excess fluid.
There is a different look to these guys. There was one more slide I did not show you where we had looked at five Kenyan runners who had the same sum for skinfold thickness that we had at the end of Ranger training. There was a big difference between these guys and the Rangers. First of all, in the Kenyans' appearance, the skin is sort of tight, and the Rangers have almost a squishy look to them. Just subjectively, there are some differences there, and we cannot explain it further.
DOUGLAS WILMORE: Karl, do you have biopsies on any of those people?
KARL FRIEDL: No. People have been suggesting that we should try to get those.
DOUGLAS WILMORE: You could do the hydration coefficients from your biopsies.
KARL FRIEDL: Yes, and we would like to know about the glycogen status at the same time. I mean, is there something about glycogen, perhaps, that affects the DXA [dual-energy x-ray absorptiometry] when soldiers are glycogen deprived? We talked about our other body conformational differences, but we have people who have the dimensions of these Rangers, but whose weight measures appropriately on the DXA. The weight that we measure on the scale is the weight the DXA sees, with nutritional balance, so is there something different about Rangers who are nutritionally deprived?
ARTHUR ANDERSON: I have been very interested in some of these discussions because I am going to be talking later about immunity, and it will be a completely different subject area. We have discovered that the molecular signaling that takes place that allows coordination between lymphatic tissue and components of the body so that they can respond quickly to antigenic stresses depend on extracellular fluid passing through a structure that I call the fibroblastic reticular cell conduit. It is like a blood vessel, except that it is a fiber matrix structure that pumps fluid at the speed of arterial blood flow from the skin to the lymph node in microseconds, and carries antigen in peptide form. It carries cytokines, specifically the chemokines that control the type of inflammatory cells that migrate into tissue.1
It depends on a certain amount of extracellular fluid being present in the loose connective tissues of the body. In training situations, where individuals will be constantly pumping this fluid out by the passive pumping of lymphatics back to the blood, you deplete this extracellular fluid. This phenomenon could, in fact, underlie the comment that was made about training situations resulting in decrements in immunity; there is a certain amount of extracellular fluid that is absolutely essential for maintaining normal immune signaling functions as part of the afferent phase of the immune response.
I just wanted to insert that comment here because I am not going to talk about it during my presentation later on.
ROBERT WOLFE: I would just like to say that the thing I would encourage in terms of the investigation of these body composition methods, as we become more sophisticated, is exactly how direct the link is between these units of body
composition and performance. Particularly in Dr. Vogel's introduction, he referred to a lot of the trained soldiers as being like athletes.
I think that the presumption that there is a close relationship between lean body mass and performance is a considerable exaggeration. We have had experience in two different circumstances, one of which is that we studied the U.S. swimming team over the past few years, and there is almost no relation at all between muscle mass or lean body mass and performance.
Depending on the time of year and their intensity of training, the swimmers' performance varies tremendously, but their muscle mass does not change significantly. The fractional turnover rate of the muscle may change, but there are no changes in muscle mass to speak of.
We also have studied elite female triathletes and there, again, see no relation between body composition and performance. In the females, the group we studied had a range of percentage body fat of 7 to 26 percent, and yet there was no significant relation between performance and body composition.
I think when we are looking at a large population base, it is one thing to consider the general relation between body composition and performance, but within a more narrowly defined group of subjects who all have similar body composition, then body composition will not predict performance.
DONALD McCORMICK: Just a follow-up to Bob Wolfe's comment. None of these techniques that we have heard about, save one, has the potential to go into the qualitative aspect of what the composition of the material is. Fat is fat. There are a lot of different kinds of fat, as everybody here knows, but probably nothing is known about the micronutrient compositions. Only one method, nuclear magnetic resonance, with proper probes, may someday lead us to what, in fact, is the quality.
ROBERT NESHEIM: And I suppose there is another factor that gets in there and that has to do with a person's motivation. You might think all these soldiers are highly motivated, but I assume there are different degrees of high motivation, which can also be a factor.
HARRIS LIEBERMAN: I want to make a point here that there is sort of a disconnect in that we have our two extremes. Our ability to make biophysical measurements of the composition of particular substances is clearly highly refined, and as we get to more exotic and expensive technology, it becomes even better and reaches a molecular level.
On the other hand, when we try to measure performance outcomes, we have a great deal of difficulty specifying the meaning of even the simpler ones, and it is difficult even to find an appropriate metric that we can use to pin down a particular performance.
You were saying before that it is difficult to relate muscle mass in elite athletes to their performance. On the other hand, in the general population of soldiers I believe some would say there clearly was a relationship between muscle mass and performance. So we have kind of a breakdown. What is the performance we are interested in? How can we specify it at the level of sophistication, the level of accuracy at which we can make our physical measurements? I am not sure I have a solution for that problem, but it certainly is a significant problem.
REED HOYT: I think it is important to differentiate between endurance performance and strength-related performance. I think strength-related performance is where the relationship between lean mass and performance resides, in terms of lifting so many pounds and so forth. Lean mass clearly may not be related to endurance.
ROBERT WOLFE: But even there, they obviously have weight divisions in Olympic weightlifting, because if you have more muscle, you can lift more weight, but if you take subjects of a similar body weight, it is very difficult to show any relation between total lean body mass and strength.
Nonetheless, the point is valid that the type of work that is being evaluated is important.