Biostereometric Analysis of Body Form

         MICHAEL W. WHITTLE, ROBIN HERRON, AND JAIME CUZZI

BIOSTEREOMETRICS is the science of measuring, and describing in mathematical terms, the three-dimensional form of biological objects. An extensive background to the subject has been given by Herron (ref. 1). Exposure to weightlessness results in a dramatic change in the patterns of muscular activity in the human body insofar as they control posture and are responsible for locomotion. These changes in muscular activity might be expected to result in changes in the bulk of particular muscle groups, and in the overall energy consumption of the body, which, unless accompanied by a compensating change in food intake, would cause a change in body fat. Biostereometric analysis enables changes in muscle bulk to be measured, and by examining those areas of the body containing fat deposits, enables general conclusions to be drawn about changes in body fat.

                  Method

The biostereometric measurements of the Skylab crewmen were made by four-camera stereophoto-grammetry, during the immediate preflight and postflight periods. Photographs were taken of the first (Skylab 2) crew 39, 14, and 2 days prior to launch day, on recovery day, and 19 days after recovery. The second (Skylab 3) crew was photographed 31, 14, and 5 days prior to launch day, and 1 and 31 days after recovery. The final (Sky-lab 4) crew was photographed 35, 21, 10, and 6 days prior to launch day, and on recovery day, and 1, 4, 30, and 68 days after recovery. The subjects were weighed within a few minutes of taking the photographs.

The layout of the apparatus is shown in figure 22-1. The subject stands between two control stands, which provide dimensional information in the three orthogonal axes. He is photographed simultaneously by two cameras in front, and two cameras behind. The subject is nude except for an athletic supporter, and a skullcap to press his hair down. To minimize variations in chest volume, photographs are taken in maximal forced exhalation. Between each pair of cameras is a strobe-projector, which through a focusing lens projects a pattern of lines onto the subject’s skin, making it easier to visualize during the subsequent plotting process. The cameras are modified wide-angle Hasselblads using fine-grain glass plates, for dimensional stability of the image. Duplicate sets of plates are exposed to insure against breakage or camera malfunction. The equipment is portable, and photographs were taken at Johnson Space Center, Kennedy Space Center, and on the recovery ships. After development the plates are analyzed on a stereoplotter, which derives the three-dimensional coordinates of thousands of points on the body surface, punching them on IBM cards for subsequent computer analysis. The computer program derives area, shape, and perimeter of between 80 to 100 sections of different parts of the body, and volume of any segment of the body, and of the body as a whole.

               Results and Discussion

Figure 22-2 compares measurements of leg circumference derived from stereometric analysis with tape measure circumferences obtained on the same day (ch. 21). The pattern seen in figure 22-2 is typical of all the comparisons which have been made between the two methods, the leg circumference measured by stereometric techniques exceeding that by the tape measure by 10 to 20 millimeters. There are two probable causes for this difference. Firstly, the stereoscopic photographs are made with the subject standing, whereas the tape measurements are made with the subject supine; the leg volume standing would exceed that supine by the volume of blood and interstitial fluid brought into the leg under the influence of gravity. Secondly, stereometric analysis, being a noncontact method, does not involve the compression of tissues, however small, which results from the use of a tape measure. The 10 to 20 millimeter discrepancy between the methods represents a difference in limb volume of 250 to 500 milliliters, which is entirely reasonable for the increased volume of blood and tissue fluid in the leg after transferring from the supine to the standing position. These differences would in no way invalidate comparisons made at different times on a single subject using the same technique.

Figure 22-3 is a comparison between the mean preflight weight and volume of the nine Skylab astronauts and the first postflight determination. Density for all measurements is within the range 0.98 to 1.04. This is less than the normal range of density (1.02 to 1.10) derived from hydrostatic weighing or gas displacement (ref. 2), because the volume figure includes, as well as the residual lung volume, the volume of air enmeshed in the hair, and the volume of those areas which cannot be visualized by the cameras—the axillae and perineum. These additional volumes should be reasonably reproducible from one measurement to another on the same subject, except for the hair volume, which is probably the largest single source of error. The Commander and Pilot of the final (Skylab 4) crew grew beards during the course of the flight, which again will have added slightly to their measured body volumes. It is unrealistic to calculate the density of the tissue lost during the course of the flight, as small errors in the volume determination would lead to impossible values for tissue density. Two of the crewmen— the Commander and Pilot on Skylab 4--showed little or no weight change, although a redistribution of body volume did occur. Generally speaking, the changes in weight and total body volume were of similar magnitude, and the apparent changes in density are probably not significant.

Table 22-I gives differences between the mean preflight and first postflight measurements of regional and total body volume, and body weight. It is difficult to reproduce the "cutoff" plane between the arms and the trunk, so that the arm volumes are subjected to considerable random variation, as is evidenced by the high standard deviation. There is no statistically significant difference in mean arm volume between preflight and postflight measurements. The mean losses of volume of 1.2 liters in the head and trunk, and 1.3 liters in the legs, are significantly different from zero (P<0.005). The mean preflight volume of the head and trunk is 45.8 liters, and that of the legs 18.9 liters, so that the postflight change in volume is proportionately much greater in the legs.

The head and trunk segment of the body contains the extensively fatty areas of the buttocks and abdomen. It is probable that the volume changes seen in this body segment are due more to changes in fat than to changes in muscle, whereas the legs contain much more muscle than fat, except in the grossly obese, and are more sensitive to changes in muscle bulk. Both regions of the body would be affected by changes in body fluid.

Figure 22-4 is a typical plot of the cross sectional area of the body measured against distance from the floor. The area beneath the curve represents volume. The differences between preflight and postflight measurements in the regions of the head, shoulder, and arms are slight, and result from differences in posture. Marked loss of volume is seen in the abdomen, buttocks, and calves, and a less striking loss in the thighs. The abdominal area shows a flattening of the abdomen, and the gluteal region a reduction in volume of the buttocks, both probably resulting predominantly from loss of fat. Loss of volume from the buttocks was not observed in the Commander and Pilot on Skylab 4, who lost very little weight in the course of the flight; all crewmen lost volume from the abdomen, although the loss from this area was much greater in those who showed significant weight loss. The striking reduction in leg volume immediately postflight was investigated in more detail on the final (Skylab 4) mission, in an attempt to elucidate how much of it resulted from partial muscle atrophy, due to relative disuse of the legs in the weightless environment, and how much represented a purely temporary dehydration. The absolute loss of volume from the thigh and calf was of similar magnitude, although the much smaller dimensions of the calf resulted in a much greater proportional loss and a greater change in cross sectional area, as illustrated in figure 22-5.

Table 22-II gives the differences between the volume of thigh and calf postflight in the Skylab 4 crewmen and the mean preflight value. On recovery day there was a deficit in the lower limbs of nearly 1000 milliliters, which had reduced by about a third by the following day, and had diminished to around 300 milliliters 3 days later. Both calf and thigh volume had returned to preflight values by the measurement made 30 days following recovery. It is clear that at least part of the deficient volume must represent missing fluid, which is replaced within a day or two of recovery, but there is probably also a reduction in bulk of the tissues of the leg. If, as seems probable, this loss of tissue represents partial atrophy of the leg muscles due to relative disuse in zero-gravity, it would probably be restored fairly rapidly on return to Earth, so that the 300 milliliters deficit measured on day 4 postflight may be an under estimate of the total leg muscle lost during the flight.

The mean loss of leg volume on recovery day was 1.68 liters for the Skylab 2 crew, and 1.12 liters for the Skylab 4 crew. The mean loss on day 1 postflight was 1.06 liters for the Skylab 3 crew, and 0.77 liters for the Skylab 4 crew. While it is not possible directly to compare the Skylab 2 and Skylab 3 crews, there does appear to be a decrease in the loss of leg volume on succeeding missions. On the basis of these measurements, it seems likely that in-flight exercise, which was increased on successive flights, may have acted in opposition to the postflight loss of leg volume. How much of this opposition is mediated by the prevention of muscular atrophy, and how much by an effect on the cardiovascular system, and hence on body fluids, it is not possible to say.

                    Conclusions

Biostereometric analysis of body form on the nine Skylab astronauts, preflight and postflight, reveals a loss of volume of one to one and one-half liters from the legs, much of which is replaced during the first 4 days postflight. It is estimated that about one third of this loss represents partial atrophy of the leg muscles due to relative disuse in zero-gravity, the remainder being due to a deficit in body fluid. Reduction in volume of the abdomen has been noted also, and this probably represents a small loss of body fluid, combined with a loss of body fat in all but two of the crewmen. Difficulties in distinguishing between the upper arm and the shoulder region have prevented any useful conclusions being drawn from the measurement of arm-volume.

In contradistinction to any other form of anthropometry, the stereoscopic photographs of the Skylab astronauts are a permanent detailed record of body form, which may be reexamined at some future date to answer new questions, or to take advantage of the increased accuracy resulting from advances in technique.

                  References

1. HERRON, R.E. Biostereometric measurement of body form. Yearbook of Anthropometry, 16:80-121, 1972.

2. WRIGHT, H.F., and J.H. WILMORE. Estimation of relative body fat and lean body weight in a United States Marine Corps population. Aerospace Medicine, 45:301-306, 1974.

 

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