ANNALS OF HUMAN BIOLOGY, 1979, VOL. 6, NO. 4, 315 336

Sheldon's trunk index and the growth of the thoracic and lumbar trunk R. N. WALKER Gesell Institute of Child Development, New Haven, Connecticut

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Received 4 December 1978; revised 23 January 1979

Summary.The trunk index (TI), a ratio of the area of the thoracic trunk to that of the lumbar trunk, is measured on a somatotype photograph marked according to defined criteria. Photographs of 82 boys from the Harpenden Growth Study were measured at ages 5 to 18 years, in an order that obscured which photographs were of the same boy at different ages. Remeasurement two months later of 12 boys at each of ages 5, 11, and 18 years showed retest correlations of 0-97 or higher for thoracic and lumbar areas separately and of about 0'95 for their ratio. When 57 boys aged 17 to 20 years were measured by another worker, their T| values correlated 0"90 with those used in this study. Inter-age correlations among the unedited TI values were approximately 0"9 between ages a year apart and declined as age differences increased. Correlations with values at age 18 increased from about 0-7 at age 5 to 0.9 by age 16. Editing was done by remeasuring all values that deviated by more than 0.05 TI units from a regression line based on each subject's total array of values. In the edited data, correlations with TI values at age l 8 increased, ranging from 0-8 at age 5 to 0-95 by age 16. Mean TI was quite stable, ranging only between 1-45 and 1.51 for the whole age span, with the lowest values appearing from 11 to 14 years. In 43 of the 59 boys whose series allowed determination of peak height velocity (PHV), a 'TI dip' appcarcd: onc to three TI values fell more than 0'05 TI units below the boy's overall regression line shortly before PHV. Distance and velocity curves are given for growth of the thoracic and lumbar trunk areas. Peak velocity of growth of the lumbar area occurred on average a little earlier than that for the thoracic area; the TI dip was in part a result of this. Alterations of fat distribution as seen by skinfolds probably also contributed. Judging by their individual regression lines, about 80% of the boys showed no more than chance variation from a horizontal slope, their Tl neither increasing nor decreasing overall. An additional 10% appeared to show significant slopes only because their series started or ended too near their Tl dips. The remaining 10% of boys appeared to show real changes in TI as they grew. Examples of the most extreme changes are shown. 1.

Introduction Sheldon has proposed the trunk index as one measure of body shape. This is a ratio of the area of the thoracic trunk to that of the lumbar trunk, as measured on a standard somatotype photograph (Sheldon, Lewis and Tenney 1969). The photograph is marked so as to bound the trunk at the neck and shoulders, to separate legs from trunk at the level of the gluteal fold, and then to divide thoracic from lumbar trunk by a plane halfway between the lowest border of the ribs and the crest of the pelvis (see figure 1 and appendix). These markings are made on or transferred to both frontal and rear views, the bounded areas are measured by planimeter, and the averaged frontal and rear thoracic areas divided by the averaged lumbar areas. The resulting trunk index (TI), Sheldon reported, has two useful properties. First, it relates negatively to endomorphy and positively to mesomorphy, and correlates so highly with the difference between the two that it can be used as an objective definition of the quantity mesomorphy minus endomorphy. Second, the TI of an individual was said to remain constant over time and ordinarily to be unaffected from early childhood onward by maturation, nutritional status, or exercise.

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316

R. N. Walker

Figure 1. Somatotypephotograph marked for measurementof TI. The first claim seems on the face of it reasonable: mesomorphs have broad shoulders and chests relative to their hips and have low waistlines; endomorphs have broad, padded hips relative to shoulders and chests, and have high waists. To set this index as one of the parameters for measuring somatotype is a matter of choice of definition; it remains to be seen how somatotypes so measured will relate to somatotypes determined by earlier methods. The assertion of constancy of TI is an empirical matter, however. It seems plausible that one could locate in adults a dividing line above and below which body tissue (mostly fat, presumably) would be gained or reduced in proportional amounts, thus maintaining a constant ratio once skeletal growth had been completed. That the same line could similarly serve as a balance point for growth of the bony framework seems remarkable. It would mean, for example, that the measure was unaffected by growth at puberty, when boys' shoulders broaden relative to their hips while girls' hips grow more in both bony and fatty tissues, relative to their shoulders and chests. Very little has been published concerning either the TI or the thoracic or lumbar trunk areas considered separately. Sheldon has briefly described the determination of TI and has listed five samples in which it was found to be a constant for all subjects despite other bodily changes: in the Berkeley growth studies, in which subjects were followed from early childhood to maturity; in a class of 200 college freshmen followed up 40 years later; in the Minnesota semi-starvation studies, in which young adults lost

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Sheldon's trunk index

317

25-40~o of their initial weight; in a nutrition clinic series of subjects reducing under medical supervision; and in a West Point study, following four years of body conditioning. In addition, he reports that 46 pairs of identical twins showed identical TIs within pairs. None of these studies has been published. Singh (1976) has reported the growth of the TI and of the thoracic and lumbar areas separately in 15 boys of the Harpenden Growth Study. He gives no information on interage correlations for TI but reports a sharp decline in its mean, from about 1.60 at age 5½ to about 1.25 at age 15½,though between ages 9 and 20 it ranged within +0-05 points of 1'30. However, Walker (1978) reported that for 100 New Haven boys whose photographs were measured by him at ages 2 to 4 years and by Sheldon's assistant, Mrs Paschal, at ages close to 16 years, no difference appeared in mean TI (1.47 for both). For 50 girls measured the same way, a small but significant difference appeared (1.31 at the earlier ages, 1-27 later). Correlations between the measurings were 0.72 for the boys, 0-63 for the girls. Growth studies of the thoracic and lumbar trunk regions are also lacking, except for the linear dimensions of biacromial, biiliac, and bitrochanteric diameters, described in many studies (e.g., Simmons 1944, Tuddenham and Snyder 1954, Tanner and Whitehouse 1979), and for chest breadth, described in a few (e.g., Shuttleworth 1939). These have aimed at measuring only skeletal dimensions, by site selection and measurement technique; growth of the soft parts included in the outlines of thorax and hips has not been described. The present paper explores growth of the upper and lower trunk and of the trunk index in photographs of a longitudinal sample of boys. It sets aside for another paper the question of how somatotypes based on TI, along with height and ponderal index, relate to earlier versions of the somatotype.

2.

Subjects and methods Subjects were those 82 boys from the Harpenden Growth Study (Tanner 1953, 1962, Tanner, Whitehouse, Marubini and Resele 1976) who had the longest runs of somatotype photographs. Living in a children's home in England, these boys composed a well cared for, well nourished group, of European and largely workingclass background. They were measured and photographed every 6 months and every 3 months during puberty at dates corresponding closely to their birthdays and equidistant points. Their birthday photographs only, from age 5"0 to age 18.0, were used in this analysis. In the cases of 8 boys missing an annual photograph at an age between 11 and 15 years, a picture made 3 months earlier or later was substituted. For 9 boys lacking a photograph at age 18, one at 19 or 20 was measured. In all, 859 sets of photographs were measured, the average boy contributing 10-5 pictures. Measurements The photographs, enlarged to ~ life size, were marked under a large magnifying lens, following methods described in the appendix. The marking was made on a sheet of acetate taped over the photograph. Measuring was also done under the magnifier, the optical planimeter tracing the contours seen through and marked on the overlay and the area in cm 2 read from its vernier dial. After each picture was measured the overlay was erased and reused. To mark the photograph for measurement requires that the marker locate 19 points on the photograph. Demanding so much individual judgement, the TI is a somewhat plastic measure, more susceptible to expectations than most physical growth measures.

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318

R. N. Walker

It was i m p o r t a n t , therefore, to m a k e the d e t e r m i n a t i o n of t h o r a c i c a n d l u m b a r areas for the s a m e b o y at different ages as i n d e p e n d e n t as possible. T o d o this, all b o y s of an age were m e a s u r e d at one time, r a t h e r t h a n all the ages for o n e b o y at a time. Age groups were m e a s u r e d in a staggered o r d e ~ a g e 5, age 10, age 15, age 6, age 11, e t c . - - t o reduce the building up o f the m a r k e r ' s familiarity with the subjects. Since a m e t r e m e a s u r e was included in each p h o t o g r a p h , m e a s u r e m e n t s could be c o r r e c t e d for slight v a r i a t i o n s in p h o t o g r a p h i c e n l a r g e m e n t a n d c o n v e r t e d to life size equivalents by m u l t i p l y i n g linear m e a s u r e m e n t s by 1000/length of p h o t o g r a p h i c image of the m e t r e stick in ram, a n d m u l t i p l y i n g areas b y the square of t h a t value. The r e p o r t i n g of values to life scale should allow c o m p a r i s o n with d a t a from studies using different sizes of p h o t o g r a p h i c negatives a n d enlargements. Reliability

T w o aspects of reliability of the m e a s u r e m e n t s were evaluated. First, a b o u t two m o n t h s after they h a d first been m e a s u r e d , 12 p h o t o g r a p h s at each o f three ages were again m a r k e d a n d m e a s u r e d ~ i f f e r e n t b o y s at each age. The initial m a r k i n g having been m a d e on an overlay, this r e - m a r k i n g was uninfluenced by earlier j u d g e m e n t s . C o m p a r i s o n of the initial a n d later m e a s u r e m e n t s is m a d e in table 1 for t h o r a c i c and l u m b a r t r u n k a r e a s a n d for T! at ages 5, 11 and 18 years. F o r the t h o r a c i c a n d l u m b a r areas, r e p r o d u c i b i l i t y o f m e a s u r e m e n t was surprisingly high. The s t a n d a r d d e v i a t i o n s of differences between first a n d second measurings were 1-2~o of the m e a n m e a s u r e m e n t at each age a n d c o r r e l a t i o n s r a n g e d from 0.97 u p w a r d s . The T ! itself showed nearly as g o o d repeatability, with SDs o f differences being 0'03 to 0.04 T ! units. Its reliability was a p p r o x i m a t e l y the p r o d u c t of the reliabilities of its c o m p o n e n t s a c o r r e l a t i o n of a b o u t 0.95 between occasions.

Table 1. Correlation coefficients and differences between measurements made two months apart for 12 boys at each of three ages. Age Measure 5

11

18

Thoracic trunk area

Mean in cm2, first measuring Mean difference, first minus second measuring SD of differences SD of differences as percentage of mean Correlation, first vs second measuring Lumbar trunk area Mean in cm 2, first measuring

Mean difference, first minus second measuring SD of differences SD of differences as percentage of mean Correlation, first vs second measuring

7.71 0.02 0.08 1.07% 0.99 5.11 0.00 0.11 2.23% 0.97

11-33 0.08 0.16 1.41% 0.98 7-69 - 0.05 0.14 1.83~ 0.99

18.55 0.07 0.19 1.01% 0.99 12.43 - 0.02 0.16 1.29% 0.99

Trunk index

Mean in TI units, first measuring Mean difference, first minus second measuring SD of differences SD of differences as percentage of mean Correlation, first vs second measuring

1.51 0.02 0.04 2.73~ 0.92

1.49 0.02 0-04 2.68% 0.96

1.50 0.01 0.03 2.23% 0.97

Sheldon's trunk index

319

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Second, the photographs of 57 of the boys, at ages 17 to 20 years, were marked and measured independently by Mrs Paschal. She chose to measure contact prints, which offer trunk areas only a fifth the size of the enlargements, and she reported that she found many of the photographs poorly posed for taking T! the shoulders not well centred or the subject not standing straight in the side picture. Nevertheless, her TI measurements correlated 0"90 with those used in this study---just about what one would expect if her own reliability of measurement for TI, like Walker's, is about 0.95. With a mean of 1.57, SD of 0.11, her measurements averaged 0.05 TI units higher than Walker's and the SD of their differences was 0.06.

Editin9 The procedure of measuring each photograph of a boy independently of his other photographs, though necessary for a valid test of the stability of TI, lost one important advantage of longitudinal methods: the chance to edit the data using individual age-toage comparisons. An editing step was added, and the critical findings concerning interage stability are reported for the data both before and after editing. Editing was done as follows. After all measurements had been made and TI computed, each subject's series of TI values was plotted against age on an individual graph. Figure 2 gives an example. A regression line was drawn giving the least-squares straight-line fit to his array of values, and lines parallel to this were drawn 0.05 TI units above and below it. (Sheldon considered _+0"05 to be the limits of permissible discrepancy between TIs for the same subject on different occasions; it is about ½SD for all ages in this study.) Values lying outside these boundaries were all re-marked and remeasured. The re-marking was done without reference to previous markings, which had left no record on the photograph themselves. In the editing process 124 values were changed: an average of 1.5 values in the average boy's record of 10.5. Nearly all the remeasured values moved closer to the regression line, but 81 of them remained outside the _+0-05 limits. Eighteen of the changes were corrections of errors of recording, calculation, etc., many of them fairly large. The remaining changes were mostly small, few exceeding 0.08 units. Some 1.8

1,fi

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O-

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1.2

PHV 1.0

i

i

7

i

i

9

v

11

f

13

i

i

15

i

17

19

AGE

Figure 2.

T r u n k index measurements for one boy, with least-squares regression line and parallels 0-05 TI units above and below it.

320

R . N . Walker

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changes simply reflected improvement of skill in marking; the earliest-marked ages had the most changes. Others showed the advantage of longitudinal comparisons, as when a boy's whole growth series showed the persistence of a lower, secondary gluteal fold, which had been taken to be just a shadow in one picture, giving a discrepant value at that age. 3. Results Trunk index Means and interage correlations. Table 2 gives the mean values for TI at each age and the correlations for each pairing of ages. The values above the empty diagonal are for the data before editing. They show an essentially unchanging mean TI, ranging only between 1-45 and 1.51 over the age span, with a small dip in the ages from about 10 to 13. The inter-age correlations are highest along the diagonal, close to 0"9 between ages a year apart, and decline as the distance increases between ages paired. The last column, giving correlation with final TI, shows a rise from about 0.7 to 0.9 over the 14 ages. The section of table 2 below the diagonal shows results following editing of the data. The changes from the upper to the lower half of the table are not great. The means are scarcely changed; the correlations increase slightly, especially at the younger ages, so that correlations with terminal status range from 0"80 to 0.95, with the expected dip in correlations in early puberty. The similarity of the lower to the upper half of the table is taken to indicate that the amended correlations are not mainly the result of expectations but essentially a sensible regularizing of already substantial relationships. Further results will be presented only for the revised, edited data. Pubertal dip in TI. Inspection of individual subjects' curves showed that the dip in mean TI occurring around 11-13 years was not a chance phenomenon. It was instead a faint representation of a development appearing more sharply in individual records but at varying ages, so that it was smoothed out in the means. Fifty-nine subjects--72% of the sample--had records complete enough through the adolescent period to allow determination of age of peak height velocity (PHV). These determinations had already been made by Tanner and Whitehouse, for overlapping periods of one-year duration starting at successive quarter-year intervals (Tanner, Whitehouse and Takaishi 1966). Forty-three of the 59 showed near PHV a dip of one to three TI values large enough to fall below the - 0.05 parallel used in editing the data, though only 10 of these same boys had any other TI values falling outside the +_0.05 limits after editing. The 16 boys lacking so extreme a TI dip all showed within the _+0.05 limits a value identifiable as a near-PHV dip, once one looked for it, though occurring within these limits it could arguably be a chance fluctuation. Figure 3 shows the joint distribution of ages of greatest TI dip and peak height velocity for the 43 boys with clear TI dips and the 16 boys with more tentatively identified ones (less than 0.05 below the regression line). The lowest points of the TI dips mostly occurred from just before to 3 years before PHV, three coincided with PHV, and five occurred within a year following PHV. Some instances of dips occurring at or slightly after the PHV peak may result from PHV having been determined from quarter-yearly observations while TI was measured only at yearly intervals. Not only was the dip sharply defined in most boys, in most it was brief--a spike downward lasting one or two years, followed by a prompt return to within the _+0.05 limits. Figure 1 is a typical curve. Figure 4 depicts the mean TI curve when these 59 subjects were aligned according to the lowest point of the TI dip, with other values

53

58

67

77

74

77

69

65

59

53

57

53

45

54

6

7

8

9

10

11

12

13

14

15

16

17

18

18+

1"51

1.51

1.51

1.49

1.48

1.46

1.45

1.45

1.47

1-48

1.49

1.50

1.49

1.49

1.49

Mean

0"09

0-10

0.09

0.09

0.10

0.10

0-10

0.10

0.11

0-11

0.10

0.09

0-08

0.08

0-08

SD

0.90 (43) 0.85 (41) 0-86 (40) 0.84 (39) 0-84 (36) 0.73 (39) 0.71 (33) 0.70 (30) 0.71 (27) 0.80 (24) 0.79 (28) 0.78 (25) 0-82 (24) 082 (29)

43 1.46 0.09

0.88 (51) 0-88 (50) 0.88 (49) 0.87 (46) 0.80 (49) 0.79 (43) 0-75 (40) 0.78 (36) 0.80 (31) 0.80 (34) 0.80 (31) 0-87 (28) 0-86 (35)

0-87 (43) --

53 1.48 0-09

6

0.92 (57) 0.90 (56) 0-90 (52) 0.85 (54) 0.84 (46) 0-79 (42) 0.79 (38) 0.81 (34) 0.77 (38) 0.86 (34) 0-88 (31) 0-85 (40)

0.77 (41) 0-84 (51)

58 1.50 0.08

7

0.93 (64) 0.94 (60) 0,87 (62) 0.91 (54) 0.83 (51) 0.78 (45) 0,80 (42) 0,80 (45) 0.84 (42) 0.89 (37) 0-88 (46)

0.80 (40) 0,82 (50) 0.88 (57) --

67 1.50 0.09

8

0.95 (72) 0-93 (74) 0.89 (66) 0-88 (61) 0.87 (55) 0.85 (51) 0.81 (53) 0-84 (49) 0.87 (41) 0-85 (50)

0-76 (39) 0.78 (49) 0.85 (56) 0-90 (64)

77 1.48 0-10

9

0.91 (72) 0.89 (65) 0.87 (61) 0.87 (55) 0.88 (49) 0.80 (53) 0.86 (48) 0.90 (41) 0"88 (49)

0.81 (36) 0.81 (46) 0.83 (52) 0.89 (60) 0.92 (72) --

74 1.46 0.11

10

0.92 (69) 0-89 (64) 0.86 (58) 0.83 (52) 0.76 (53) 0.80 (49) 0.85 (42) 0-81 (49)

0.73 (39) 0.77 (49) 0-80 (54) 0.81 (62) 0.89 (74) 0.89 (72) --

77 1.45 0.11

11

0.89 (63) 0,87 (57) 0-82 (51) 0.79 (51) 0.81 (47) 0.87 (40) 0'84 (46)

0.64 (33) 0-75 (43) 0,84 (46) 0.81 (54) 0.88 (66) 0-87 (65) 0.90 (69) --

69 1-45 0.I0

12

0.90 (58) 0.84 (52) 0.86 (52) 0.87 (47) 0.90 (41) 0'86 (46)

0.59 (30) 0-70 (40) 0.75 (42) 0.78 (51) 0.84 (61) 0-84 (61) 0.87 (64) 0-87 (63) --

65 1-46 0.10

13

t TI for age 18 used where available; where absent, value for age 19 or 20 substituted.

43

N

5

0-90 (52) 0.90 (48) 0.89 (43) 0.89 (38) 0"87 (43)

0-58 (27) 0.65 (36) 0,74 (38) 0.74 (45) 0-83 (55) 0.83 (55) 0.85 (58) 0.86 (57) 0.89 (58) --

59 1.48 0.10

14

0.93 (45) 0-90 (41) 0.94 (37) 0"91 (42)

0.72 (24) 0.69 (31) 0.77 (34) 0.73 (42) 0-81 (51) 0.85 (49) 0-81 (52) 0.81 (51) 0.82 (52) 0.87 (52) --

53 1,48 0-10

15

0-94 (49) 0.96 (39) 0"95 (44)

0.63 (28) 0.60 (34) 0-70 (38) 0-69 (45) 0.74 (53) 0.71 (53) 0.75 (53) 0.75 (51) 0.84 (52) 0.90 (48) 0.92 (45) --

57 1.51 0-09

16

0.95 (41) 0"95 (45)

0-71 (25) 0.67 (31) 0-79 (34) 0.77 (42) 0-79 (49) 0.78 (48) 0.76 (49) 0.78 (47) 0.85 (47) 0.86 (43) 0.90 (41) 0.93 (49)

53 1.50 0.09

17

0-62 (24) 0-67 (28) 0.77 (31) 0.71 (37) 0.76 (41) 0-79 (41) 0.79 (42) 0.87 (40) 0-84 (41) 0.86 (38) 0.93 (37) 0.93 (39) 0.92 (41)

45 1.50 0.10

18

0.68 (29) 0-68 (35) 0.77 (40) 0.73 (46) 0.77 (50) 0-77 (49) 0.76 (49) 0.85 (46) 0.82 (46) 0.85 (43) 0.88 (42) 0.92 (44) 0.92 (45)

54 1.50 0.10

18++

Numbers, means, standard deviations, and intercorrelations for trunk index in 82 Harpenden boys aged 5 to 18 + years, in unedited date (above the diagonal) and edited data (below the diagonal}.

5

Age

Table 2.

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R. N. Walker

322

17

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Ann Hum Biol Downloaded from informahealthcare.com by Bausch & Lomb IOM on 01/13/15 For personal use only.

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I 11

l 12

I 13

I 14

AGE AT P E A K H E I G H T

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I

17

VELOCITY

Figure 3. Joint distribution of ages of greatest TI dip and peak height velocity for 43 boys with clear TI dips (black dots) and 16 boys with less marked dips (white dots).

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1.N -8

-'7

26

25

24

22 21 6 Y~A~s VROMTZ DzP

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Figure 4. Mean trunk index curve for 59 boys aligned by lowest point of TI dip.

ranged out by years before and following that point, rather than by chronological age. The curve may be somewhat exaggerated, capitalizing on chance fluctuations of measurement as well as real changes in selecting the lowest TI value for aligning of subjects. These findings indicate that for a short time before puberty the lumbar trunk area grows more rapidly than is necessary to preserve its otherwise steady proportionate

Sheldon's trunk index

323

ratio to the thoracic trunk, and that the latter theh has a growth increase, about coincident with the height-growth spurt, and re-establishes the earlier ratio. This can be better evaluated by examining these components directly. Thoracic and lumbar trunk segments Growth of the thoracic and lumbar areas is shown in the mean values of table 3 and the mean distance curves graphed in figure 5. Figure 5 also graphs thoracic area divided by 1.5: the curve that lumbar area must follow if mean TI is to maintain a constant

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Table 3. Means and standard deviations for heights and areas of thoracic and lumbar segments of the trunk for 82 Harpenden boys.

Age

N

Thorax Lumbar Thorax area Lumbar area height (cm) height (cm) (cm 2) (cm 2) Mean SD Mean SD Mean SD Mean SD

5 6 7 8 9 10 11 12 13 t4 15 16 17 18

42 53 58 67 77 74 77 69 65 59 53 57 53 45

26-7 28-0 29"1 30"3 31-5 32"4 33"4 34"4 35'8 37-4 39'5 41-3 42'4 43"0

1-2 1-2 1'2 1"3 1"3 1"4 l'4 1-5 2-0 2'2 2'8 2"3 1'9 1"9

17"3 18-0 18'7 19'3 20"1 20"9 21'6 22"3 23-2 24"1 25'2 26'2 26'6 27"2

0'9 1'0 1-0 1"0 1'2 1'3 1"3 1'3 1'4 1'5 1-7 1'4 1-3 1-4

525'2 33'6 557'5 35-9 5 9 9 " 0 40"8 6 4 2 " 7 44-3 694'1 50"6 7 4 0 - 9 52"0 7 8 8 - 5 57"1 836'6 64"4 909'5 88'0 994"6 112-9 1100-4 129"3 1193"8 114-3 1255-7 100'6 1300'8 108'5

354"4 376'3 401"8 430"6 468"1 503'4 541"1 578"9 630-2 685'3 745'4 804'4 833-3 864-7

26'7 30"2 33-0 37"2 48'7 54"1 62-1 69'7 78'8 88"3 89-9 78"I 75-2 86'0

1300

1100

900

THORACIC AREA

\/

7OO

LUMBAR

/~.

Sheldon's trunk index and the growth of the thoracic and lumbar trunk.

ANNALS OF HUMAN BIOLOGY, 1979, VOL. 6, NO. 4, 315 336 Sheldon's trunk index and the growth of the thoracic and lumbar trunk R. N. WALKER Gesell Insti...
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