ANNALS OF HUMAN BIOLOGY, 1978, VOL. 5, NO. 5, 469--482

Relationship of anthropometric dimensions to lean body mass in children

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M. H. S L A U G H T E R , T. G. LOHMAN and R. A. BOILEAU Physical Fitness Research Laboratory, University of lllinois at Urbana-Champaign

[Received 12 July 1977;revised 24April 1978] Summary. This study is designed to compare the predictability of lean body mass, as measured by whole-body 4°K spectrometry, from skinfolds, circumferences and skeletal widths in children 7 to 12 years of age. The specific skinfold sites were back, upper arm, side, waist, abdomen, and calf; the circumference sites were forearm, upper arm (flexed), wrist, thigh, calf, and chest (deflated); skeletal widths included wrist, knee, ankle, elbow, shoulder and hip. In a group of 163 boys, three skinfolds and body weight accounted for 89.7 % of the variation in LBM, two circumferences and height and weight accounted for 87.2 % of the variation in LBM, and two skeletal widths and height and weight accounted for 87.4 % of the variation in LBM. Combining all measurement variables into one analysis resulted in five significant variables: weight, side skinfold, abdomen skinfold, forearm circumference and chest circumference with the coefficient of determination 90.6 %, only slightly higher than with weight and three skinfolds. The significant variables from the combined analysis were then used to predict LBM in five separate age groups of boys and a sample of 44 girls. In general, weight, forearm and chest circumference contributed positively to LBM and side and abdomen skinfolds contributed negatively. The regression coefficients for each site were not significantly different among age groups. LBM in children can be estimated from skinfolds, circumferences or skeletal widths with considerable success, as has been shown to be the case in collegeage adults.

1. Introduction Little research has been conducted to evaluate various combinations of anthropometric dimensions for prediction of body composition in prepubescent children. In adults, several investigators have studied skinfolds, circumferences and skeletal widths as predictors of lean body weight and percentage fat, estimated from body density, and found that multiple regression equations using between two and five variables account for much of the variability in body composition (Katch and McArdle, 1973; Wilmore and Behnke, 1969, 1970; Steinkamp, Cohen, Siri, Sargen and Walsh, 1965). In addition, both Wilmore and Behnke (1969, 1970) and Katch and McArdle (1973) found little difference in prediction accuracy whether skinfolds or

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circumferences or a combination of the two were used to predict lean body mass (LBM) or body density. In children and adolescents, several studies have shown skinfolds to be useful predictors of body fatness (Michael and Katch, 1968; Young, Sipin and Roe, 1968a; Forbes and Amirhakimi, 1970; Parizkova, 1961 a, b; Lohman, Boileau and Massey, 1975). Measurements of body circumferences and skeletal widths in relation to body composition, as estimated from body density or potassium, have not been compared to skinfolds with children. This study was designed to compare the predictability of LBM, as measured by whole-body 4°K spectrometry, from skinfolds, circumferences and skeletal widths in boys 7 to 12 years of age. In addition, the results derived from the boys were applied to a sample of prepubescent girls over the same age range. It was hypothesized that skinfolds and body weight are the best predictors of LBM, but that the use of circumferences and skeletal widths also will yield accurate LBM prediction. Further, it was hypothesized that within the 7 to 11 year-old age group, one regression equation will be applicable to the various ages of boys. 2.

Methods The subjects in this study were 163 boys and 44 girls aged 7.0-11.9 years. The boys and girls were participants in the University of Illinois Sports-Fitness Programme during summers of 1972-1976. None of the girls had reached menarche. In most cases the measurements were taken during the first five weeks of the eight-week programme. The sample includes a wide range of children from very active and skilled to very inactive and unskilled. The weights, height and skinfolds of participants of this programme during 1970 t o 1972 have previously been shown to be slightly larger than the norms (Lohman, et aL, 1975). The present sample represents largely middle and upper middle socio-economic backgrounds. For the 1972-76 period, four subjects were black. Body potassium and selected skinfold and anthropometric dimensions were taken on all subjects twice within seven days.

Body compositionprocedure Body potassium was assessed by whole-body 4°K counting using the 4re liquid scintillation counter at the University of Illinois (Twardock, Lohman, Smith and Breidenstein, 1966). Each subject was counted on each of two days within a 10-day interval for two consecutive four-minute counting periods preceded and followed by four-minute background counts. A known standard of ~°K activity was counted during each testing session to monitor the instrument counting efficiency. Body potassium was computed from the 4°K assay as described by Boileau, Massey and Misner (1973). Lean body mass was calculated from the mean of two measurements of body potassium using the constant of 2.66 g K/kg proposed by Forbes and Hursch (1963).

Anthropometricprocedure The anthropometric dimensions which were taken included skinfolds, body circumferences and skeletal widths. Three consecutive measurements were taken at each site on each of two days and the mean of the three measurements for each day was used as the measurement for a given site. All skinfold thickness measurements were made within a Harpenden caliper on the right side of the body. Different technicians completed the anthropometry each year, but all were trained by one investi-

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gator and the intra-examiner reliability of each technician was measured and found to be comparable with a subsample recorded. The specific skinfold sites measured were back, upper arm, side, waist, abdomen and calf as described by Allen, Peng, Chen, Huang, Chang and Fang (1956). The descriptions are as follows:

Back (2 centimetres below the inferior angle of the scapula) Upper arm (vertical fold on mid-posterior line midway between acromion and olecranon process while elbow is flexed at 90 ° and the upper arm is extended vertically downward) Side (on midaxillary line at the level of fifth rib at the 45 ° diagonal) Waist (on midaxillary line 2 centimetres above the iliac crest) Abdomen (2 centimetres to the right of the umblicus) Calf(2 centimetres below popliteal area on mid-posterior line) The specific circumference sites measured were forearm, upper arm (flexed), wrist, thigh, calf and chest (deflated). The circumference measurements were as follows:

Forearm (maximal girth with muscles fully contracted, the elbow extended and the hand supinated) Upper arm (flexed) (maximal girth of the mid-arm when flexed to greatest angle with the underlying muscles fully contracted) Wrist (minimal girth just distal to the styloid processes of the radius and ulna) Thigh (maximal girth with the subject bearing total weight on measured leg) Calf (maximal girth with the subject bearing total weight on measured leg) Chest (deflated with subject in anatomical position and chest muscles fully contracted) The specific skeletal widths included hip, ankle, wrist, knee, shoulder and elbow. These width measures are as follows:

Hip (distance between the most lateral projections of the iliac crests) Ankle (distance between the most lateral projections of the malleoli with the subject's knees flexed at 90 ° on a bench) Wrist (distance between the styloid processes of the ulna and the radius) Knee (distance between the condyles of the femur with the subject in a sitting position and his knee flexed in a 90 ° angle) Shoulder (distance between the most lateral projections of the acrominal processes with elbow next to the body and the hands resting on the thighs) Elbow (distance between the condyles of the humerus and with the elbow flexed and hand supinated) In all cases the mean of 2 days of measurements were used as the represented value. Step down multiple regression analysis was used to derive multiple regression equations for prediction of LBM from skinfolds, circumferences and skeletal widths. In the first step of this analysis all skinfolds were used as predictors of LBM. The skinfold regression coefficients with the lowest t values were dropped from the second analysis up to no more than half the total number of independent variables. This procedure was repeated eliminating up to half the independent variables until only statistically significant variables remained. 3.

Results The physical characteristics of the boys (Table 1) indicate that for height and weight the children were on average 1 to 4 cm and 1 to 4 kg greater than that found

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at each age group in a national sample of children (National Center for Health Statistics, 1973). Upper arm, back and side skinfolds were also 1 to 4 mm higher for each age group than that found in a national sample (National Center for Health Statistics, 1972). In all cases, the greater deviations were for the 10 and 11 year olds. These results probably reflect the higher socio-economic background of the subjects than the national sample. Lean body mass estimated from body potassium ()?= 67- 6 kg) was in agreement with other investigations (Allen, Anderson and Langham, 1960; Forbes, 1972) and somewhat greater than Oberhausen, Burmeister and Huycke (1965). Age (yr)

Height (cm) Weight (kg)

Age group

N

.~

SD

X

SD

.~

SD

7.0-7"9 8.0-8.9 9.0-9.9 10.0-10.9 11.0-11.9

23 35 35 35 35

7.5 8"5 9.5 10-4 11-6

0.33 0-23 0.25 0.27 0.30

126.5 131.1 136-2 144.1 148.2

6.1 6'2 4-6 7"3 4.8

25'7 28"1 31-6 37,6 41.1

4-0 4"7 5-0 7"3 8.7

% fat

Side skf (mm)

Abd skf (mm)

K (g) X

LBM (kg)

SD

.~

53.5 8.0 20-1 58.3 8.5 21'9 64-9 8-2 24-4 74-5 11.2 28"0 81-9 12.8 30.8

SD 3.0 3.2 3'1 4.2 4.8

Chest Forearm (deflated) circum (cm) circum(cm)

Age group

N

X

SD

)7

SD

X

SD

X

SD

37

SD

7.0-7.9 8.0-8.9 9-0-9.9 10.0-10-9 11.9-11.9

23 35 35 35 35

20"5 21.7 22"3 24.4 23'8

5-6 6.2 7-5 9.6 8-3

5.2 6.0 6"4 9.5 9-0

2.0 3.2 3"8 6.5 5"5

6-7 7.8 8"6 13.6 14.1

4.4 5-1 5"9 8-8 8"7

18.9 19.5 20.4 21.6 22.1

1-1 1-4 1-5 1.7 1-8

59"3 60,1 63'8 66-7 69'1

4"1 4.2 3.9 5-2 6'5

Table 1. Physicalcharacteristics of boys by age group (N= 163). Reliability coefficients for body composition measures between test days for a subsample of boys ( N = 8 I) were 0.97 for LBM. The reliability coefficients for anthropometric dimensions were all above 0-90 and similar in magnitude to those found by Lohman et al. (1975) for skinfolds (Table 2). The technical error of measurement of the various sites were determined using a subsample of boys (Table 2). These results show that the measurement error as determined by the standard deviation of difference between skinfold measurements taken by the same investigator on different days was somewhat larger for calf and side as compared to upper arm and abdomen. The measurement error for the circumferences was quite similar (0.99-I .22) except for the wrist which was somewhat lower (0.29). Zero-order intercorrelation coefficients for body composition and structural measures are found in Table 3. LBM is correlated with body weight and height, 0.89; with forearm circumference, 0.86; and chest circumference, 0.84. The correlation of percentage fat with side skinfold is 0.72 and with abdomen skinfold, 0-75. To study the association of LBM with circumferences, skeletal widths and skinfold measurements, multiple regression analysis was used (Table 4). LBM was initially estimated from three separate analyses: (1) using height, weight and skinfolds; (2) using height, weight and circumferences; and (3) using height, weight and skeletal

Anthropometric dimensions and lean body mass Variable

rt

SD diff:~

t§

0.98 0.96 0-96

0" 91 0.75 1.17

2.20 0" 87 0.34

0.98 0-93

1- 51 1-42

1.33 0-30

0-98 0"99 0.96 0.97 0-98 0.98

1-20 1-18 0-29 0.99 1-22 I. 16

0"60 I. 17 1.49 2-41 I. 81 0" 57

0" 92 0.93 0.96 0.98 0-95 0-97

0.53 0.31 0-17 0.19 0-45 0.40

0" 87 1.38 1 "46 1.10 0-37 0.41

473

Skinfolds Back (ram) Upper arm (mm) Side (ram) Waist Abdomen (mm) Calf (mm)

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Circumferences Forearm Upper arm Wrist Thigh Calf Chest (deflated)

Widths Hip Ankle Wrist Knee Shoulder Elbow

t Reliability coefficient between measures on day one versus day two in 81 subjects. $ Standard deviation of the difference between two days of measurement in 81 subjects. § t ratio for test of statistical significance of mean change in measurement from day one to day two. Table 2. Reliability of anthropometric and skinfold variables (N = 81). 1

1. 2. 3. 4. 5. 6. 7. 8.

Height (cm) Weight (kg) LBM (kg) %fat Side skinfold (mm) Abdomen skinfold (mm) Forearm circumference (cm) Chest (deflated) circumference (cm) 9. Age

2

3

4

5

6

7

8

9

0.87 0.89 0-89 0-30 0-54 0"47 0'44 0.75 0-55 0-72 0.53 0-81 0.59 0-75 0.90 0.77 0.93 0-86 0.44 0-68 0-76 0.79 0.94 0"80 0.68

0"84 0.50 0"73 0.32

0"73 0.78 0"92 0-39 0-60 0-60 0.59

r>0.21, P>0.05. Table 3. Zero-order correlation coefficients for selected body composition and anthropometric measures in boys (N= 163). widths. I n each analysis the non-significant variables were eliminated in a step-down multiple regression procedure with only the significant variables remaining. T h u s , three skinfolds a n d body weight accounted for 8 9 . 7 ~ of the v a r i a t i o n in L B M (Table 4, first column), two circumferences a n d height a n d weight accounted for 87.2 ~ of the variation in L B M (Table 4, second c o l u m n ) a n d two skeletal widths a n d height a n d weight accounted for 8 7 - 4 ~ of the v a r i a t i o n in L B M (Table 4, third column). Finally, all variables were c o m b i n e d into one analysis a n d the n o n - s i g n i f i c a n t variables were again eliminated in the c o m b i n e d analysis. The coefficient of A.H.B.

2

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d e t e r m i n a t i o n from the final five significant variables: weight, side skinfold, a b d o m e n skififold, forearm circumference a n d chest (deflated) circumference, was 90"6~o (Table 4, fourth column), only slightly higher t h a n with weight a n d three skinfolds (Table 4, first column). The variables from the c o m b i n e d analysis (weight, side a n d a b d o m e n skinfolds, a n d forearm a n d chest circumferences) f o u n d to be significant for the total sample of 163 boys were then used to predict L B M in five separate age groups of boys and a sample of 44 girls (ages 7 to 11). The 44 girls were distributed over the age range in a similar pattern to the boys a n d similar m e a n age, weight and circumferences were f o u n d (Table 5). The coefficients o f d e t e r m i n a t i o n within age groups for boys 7 to I I Dependent variable Lean body mass Circumferences, Skinfolds, weight height and weight Boys Height (cm) Weight (kg) Weight (kg)

0" 86* 0.86*

Widths, height and weight

Weight, skinfolds and circumferences

Boys

Boys

Boys 0" 25":~

0" 15*

0" 20*

0" 22*

0' 62*

Skinfolds Side (mm) Abdomen (mm) Calf (mm)

-0.28* - 0" 17* - 0 " 15"

-0-31" - 0' 20*

Circumferences Forearm (cm) Thigh (cm) Chest (deflated) (cm)

1" 15" - 0.23*

0" 53' 0' 17"

Widths Wrist (cm) Shoulder (cm) Intercept R R 2 x 100"~ SEE (kg)

1 "6 0'947 89 "7 1 '7

3.49* - 0' 34* -28" 13 0'935 87-4 1.9

-24-5 0"934 87.2 1-9

- 12.56 0"952 90.6 1.7

* P~>0.05.

~"Coefficient of determination equals R 2 x 100. :~Numbers are unstandardized regression coefficients. Table 4. Association of height, weight, skinfolds, circumferences and widths with lean body mass (N= 163). Boys (N= 163)

Age (yr) Height (cm) Weight (kg) K(g) LBM (kg) % fat Side skinfold (ram) Abdomen skinfold (mm) Forearm circumference (cm) Chest (deflated) circumference (cm)

X

SD

9'6 138-0 33' 4 67.6 25"4 22'7 7" 4 10"4 20.6 64' 3

1.4 10.1 8.4 14.1 5.3 7.7 4' 9 7.5 2' 0 5- 9

Girls (N=44) .~ 9"5 135.6 32' 2 63.3 23 "8 24-8 8' 6 11 "3 20" 0 63.3

SD 1 "4 11.0 7' 5 12"2 4.6 9"0 5" 6 7.6 1" 8 5" 7

Table 5. Physical characteristics of total group of boys (N= 163) and total girl group (N=44).

Table 6.

Weight (kg) Forearm circumference (cm) Chest circumference (cm) Side skinfold (mm) Abdomen skinfold (ram) Intercept R R 2 x 100 SEE, kg N

0-56* 0- 61 0.14 -0.33 -0.20 -11.29 0.856 73.2 1.4 35

9 0.64* 0.31 0.20 -0.17 -0.31" -10.54 0.914 83 '5 1.8 35

10 0.49* 0.33 0.32 0.35* 0.17 -13.56 0-925 85.6 2.0 35

I1 O. 14 0.47 0" 18 0'23 0' 10

Polled within age group?

Boys

0-62* 0.53" 0.17" -0.31" -0.20 -12.6 0.952 90.6 1.7 163

Regression coefficient 7-I 1

*P>0.05. ? Standard error of regression coefficients pooled across age groups.

0.62* 0.76* 0.01 -0.24 -0.13 -8.2 0.909 82.6 1.7 35

8

Standard error (Sb)

0.06 0.19 0.07 0'06 0.04

Sb

Girls

0"56* 0"20 0.16 --0"24 -0'12 --4"9 0"918 84"3 1"9 44

Regression coefficient 7-t 1

Association of weight, circumferences and skinfold with lean body mass by age group and total group.

0-40* 0.92 0.23 -0.20 -0.09 -19.81 0.933 87.0 1.2 23

7

Regression coefficients

Boys, age group (years)

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0"11 0' 40 0"13 0"10 0'09

Sb

t.~

~o

12"3 0"93 86'5 1"8

0"77* (log)-- 7" 93" (log)-- 5' 66*

Parizkovat

0" 32* 0"35* --38 "9 0"93 86"4 2"0

1 "31"

0"01

0"27

Carters

3 "7 0.96 91 "4 1 "8

1 '9

-0-36*

--0.25*

5-0 0.94 88 "4

0"87* --0"40*

previous Lohman¶

0"76* --0"23*

(present) Lohman§

1.9

11'19 0-92 84-6

0" 70* (log)- 8.41" (log) - 2.05

Parizkovat

Table 7.

Prediction lean body mass from selected anthropometric variables of previous investigations.

* P>0"05. t Parizkova (1961 b). $ Carter (1972). § Lohman, Boileau and Massey (1975) (wt. upper arm and back skinfold on present population). ¶ Equation derived from previous study on boys (Lohman, Boileau and Massey, 1975).

Height (cm) Weight (kg) Back skinful (mm) Waist skinfold (mm) Upper arm skinfold (mm) Elbow width (cm) Knee width (cm) Upper arm circumference-triceps skinfold (cm) Calf circumference-calf skinfold (cm) Intercept R R 2 × 100 SEE, kg

Independent variables

Boys

Dependent variables-Lean body mass

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1 "26 -0'45 0.58* 0.09 -27-1 0-90 81-0 2.0

0-24*

Carters

Girls

6'8 0"91 82.8 2.0

--0-17

0.65" -0.19"

Lohman§

.~ .~

4a~ .-.i ox

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477

years and the sample of girls ranged from 73.2 ~ to 87.0 ~ (Table 6). The standard errors (SEE) ranged from 1.2 kg in the seven year olds to 2.0 kg in the eleven year old boys and 1.9 kg in the sample of girls. For each anthropometric site, the regression coefficients among the various age groups of boys were not significantly different (P> 0.05). Similar results were found for the total sample of girls verus the total sample of boys (column 7). In general, weight, forearm and chest circumference contribute positively to LBM, and side and abdomen skinfolds contribute negatively. To evaluate our final equation on both the lean and fat boys in our sample, the equation developed from the total sample of 163 boys for LBM was used to predict the LBM for those 23 subjects who fell one standard deviation above the mean for fatness (above 30.4~) and for those 24 subjects who fell below one standard deviation for fatness (below 15 ~). The predicted mean for LBM using the equation from the total sample on the fat subjects was 30.3 kg, compared to the measured LBM values by 4°K count of 29.1 kg. The SEE for the fat boys (36.1 ~ body fat) was 1.8 kg, within 0.1 kg of the SEE for the entire sample. The predicted mean for LBM for the lean sample was 24.6 kg as compared to 25.0 kg for that estimated from +°K measurement. The SEE for the lean boys (11.4~ fat) was 1.2 kg as compared to 1.7 kg for the entire sample. Thus, it appears that the same regression equation developed for the prediction of LBM from the sample of 163 boys can be used in both the fat as well as lean boys with a tendency to underestimate percentage fat in the fat group (2.6 ~) and overestimate percentage fat in the lean group (4.7 ~). This bias of the equation was not corrected by taking the log of each skinfold and using an equation derived on the total sample using log skinfolds as the independent variables. Furthermore, the use of the log of the skinfolds did not improve the prediction of LBM (R=0.940 with log skinfolds, R=0-952 without log skinfolds). To examine our prediction of LBM with that of other investigators, we selected variables recommended by others and used them in multiple regression analysis on our 163 boys and 44 girls (Table 7). Our coefficient of determination in boys (90' 2 ~o using two circumferences, two skinfolds and weight) was only slightly larger than the coefficient (86.5~) derived from both Parizkova's variables (1961 b) (Table 7, column l) and Lohman et al. (1975) (Table 7, column 3) and slightly larger than the coefficient (86.5 ~o) derived from variables recommended by Carter (1972) (Table 7, column 2). The SEE's in our study for the boys and girls were only slightly less than the ones derived using variables recommended by other investigators. 4.

Discussion The mean body potassium of various age groups is in general agreement with children of this age as found by others using whole-body counters. Potassium per kg of body weight for boys in our study averaged 2.02 g/kg as compared to 2.11 for the subjects of Allen et al. (1960), 2.18 (Forbes, 1972), and 2.55 (Flynn et al., 1972) in 8-11 year old boys. From the data of Oberhausen, Burmeister and Hyucke (1965) on a large sample of German children, only median weights and body potassium value are given; for body potassium, the values were 6 to 9 ~ lower than those found in our subjects for the same age group. In our study, body potassium was used to estimate LBM, assuming the potassium content of LBM is close to the adult value of 2.66 g K/kg LBM as recommended by Forbes (Forbes and Hursch, 1963; Forbes and Amirhakimi, 1970; Forbes, 1972). Use of this constant results in an average fat content between 19 and 23 ~ in 8-11 year old boys; these results are comparable to

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Slaughter et al.

M.H.

the fat content of boys estimated from densitometry (Parizkova, 1961 a; Cureton, Boileau and Lohman, 1975; Heald et al., 1963). For girls the mean fat content in our sample is 24- 8 ~ using the same 2.66 g K/kg LBM constant as in boys. While it is fairly well established that the potassium constant for the lean body mass of the adult female is between 90 and 95 ~o of the adult male (Forbes, Schultz, Cafarelli and Amirhakimi, 1968; Boddy, King, Womersley and Durnin, 1973), the difference between male and female prepubescent children is somewhat less apparent. In our study using 2.66 g/kg for female potassium content of LBM, the mean fat content of 2 4 . 8 ~ corresponds to a density of 1.041 (using the equation of Brozek, Grande, Anderson and Keys, 1963), which is in close agreement with the mean densities for girls of a similar age group (Parizkova, 1961 a, density = 1.040; Young et al., 1968a, density = 1.039).

K/LBM, g/kg Investigator Allen et al. (1960) Cheek (1968) Cureton et al. (1975)

N

Boys

N

Girls

216 7 49

2.48 2.30 2.76

166 2-55 6 2" 10 ---

Method of LBM estimation Body water from several other investigations Body water by deuterium oxide Body density by underwater weighing

Recalculation of Cheek (1968); boys~ Water content of LBM Method 1 0.718 Method 1 0' 732 Method 1 0- 795 Method 2 0.718 Method 2 0. 732 Method 2 0' 795

K content of LBM 2.30 2' 34 2.55 2.47 2- 52 2.73

t Method 1: Measurement of body water from deuterium oxide. Method 2: Estimate of body water made from actual weight and height of children and the use of nomogram (Friis-Hansen, 1961). Water content of lean body mass assumed to be 71- 8, 73.2 and 79.5 % for illustration of difficulty in arriving at a recommended K content of LBM. Table 8. Potassiumcontent of LBM in children age 8 to 11.

Very little research has been conducted on boys and girls to derive directly the potassium content of LBM. To illustrate the range of values from data in the literature, the estimated potassium content of LBM for boys and girls 8-11 years of age was calculated from the data of Allen et al. (1960), Cheek (1968) and Cureton et al. (1975) (Table 8). The potassium content of LBM was derived from the data of Allen et al. (1960), assuming a mean water content of 6 2 ~ for boys (Allen et al., 1960; Friis-Hansen, 1961; Heald et al., 1963; Novak, 1966) and 61 ~ for girls (Allen et al., 1960; Friis-Hansen, 1961; Novak, 1966; Young, Bogan, Roe and Lutwak, 1968b) between 6 and 12 years of age. A hydration of 7 3 . 2 ~ was assumed for the water content of lean body mass for both sexes. The results show little difference in potassium content between sexes with about 2.5 g/kg LBM for this age group. Cheek (1968) measured both potassium and water content in 34 children all considered physically normal on the basis of medical and laboratory evaluations, of which 7 boys and 6 girls were between 8 and 12 years of age. Assuming a 71.8 ~ water content

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of LBM, the K content was found to be 2-3 and 2.2 g/kg LBM for boys and girls, respectively (Table 8). Cureton et al. (1975) found a K content of 2.76 g/kg of LBM in 49 boys where LBM was computed from body density using Brozek's equation for percentage fat (Brozek et al., 1963). While there is insufficient evidence to establish the potassium content of LBM in prepubuscent children, it would appear that the data of Cheek (1968) may underestimate the potassium content for the following reasons: (1) the water content of the boys is higher than other studies (.17=65.2% of body weight), (2) low values of body fat content are obtained in children using 2.3 and 2.1 g/kg LBM, e.g., in our study 12 % for boys and 6~o for girls and (3) the water content of LBM may be higher than 7 1 . 8 % (Heald et al., 1963 estimated the water content of the LBM to be 7 9 . 5 % in 12 year old boys). Recalculation of the K content of LBM in boys was made from the data of Cheek (1968) to show the effect of overestimating the total body-water and underestimating the water content of LBM (Table 8). In the present study the best skinfold predictors of LBM were side, abdomen and calf rather than triceps and subscapular as found in a previous sample (Lohman et al., 1975). However, only an additional 1.3 ~o of the variation in LBM could be accounted for by the three sites over the use of triceps. The SEE in both studies was remarkably close. Two circumferences (forearm and chest) and height and weight were also found to account for nearly as much variation in LBM as weight and three skinfolds (87.2 % versus 89-7 %). Also two body widths (wrist and shoulder) and height and weight accounted for 8 7 . 4 % of the variation in LBM. These findings suggest that in children of this age group, LBM can be estimated from circumferences or widths (SEE = 1.9 kg) almost as accurately as from skinfolds ( S E E = 1.7 kg) when height and weight are known, an important application for field studies where skinfold calipers are not always available. The most precise estimate of LBM was found using weight, two skinfolds and two circumferences (90.6% variation accounted for in LBM). Part of the remaining variability is associated with the measurement of LBM by whole-body 4°K counting. An estimate of this error (standard deviation) for the mean of two measurements on separate days is 0-9 kg LBM using data collected on 154 subjects (Lohman et aL, 1975). In addition to this 0.9 kg technical error, there is biological variation in the K content of LBM from child to child. This biological variation has been estimated to be 3-0 % on a fat-free dry basis in young growing animals (Lohman, 1971), Assuming a similar percentage variation in the K content of LBM in children, a 0.8 kg L B M error (standard deviation) would occur if LBM was estimated from body potassium. Combining both technical and biological sources of error gives an estimated total error of 1.2 kg in LBM. Thus, at best, the predictability of LBM cannot exceed 1.2 kg or 95 % of the variation accounted for in LBM (R 2 x 100) even if anthropometric variables were perfectly related to LBM. It would appear that anthropometry can predict LBM with error of estimate between 1 • 7 and 1.9 kg, somewhat short of theoretical expectations (1.2 kg). Two possible reasons for the observed larger error are: (1) external body measures are not perfect indices of LBM and (2) potassium content as measured by 4°K is somewhat more variable than 3 . 0 % in the LBM of children. Similarly, the theoretical error for percentage fat can be calculated. For a child weighing 33.4 kg with a LBM of 25.4 kg, the theoretical error from 4°K measurement is 4 . 1 % fat. This calculation is based on the 1.2 kg error in LBM above and thus a 1-2 kg error in fat weight which is estimated as the difference between body weight and LBM. Also a 0.7 kg error is assumed for variation in body weight associated

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with changes in water content (2% of body weight, Siri, 1961), thus giving a total error of 1.4 kg fat or 4 . 1 % fat when expressed as a percentage of body weight. Comparing the within age-group regression coefficients with those estimated from the total group, it would appear that one regression equation can adequately be derived from the 7-11 year old sample. Much of the observed variation among age groups appears to be due to sampling error. Considerably larger sample sizes will be needed in each age group to test adequately whether such differences in regression coefficients in this sample of girls are not significantly different from those of boys. In general, for both samples, weight, forearm circumference and chest circumference are positively related to LBM and two skinfolds are negatively related. Our best anthropometric sites, forearm and chest circumference and side and abdomen skinfolds, were only slightly more accurate in estimating LBM than the sites used by other investigators (Parizkova, 196I b; Lohman et al., 1975; Carter, 1972). Thus, investigators who estimate LBM in children can use anthropometric dimensions (skinfolds, circumferences and/or widths) with considerable success, as has been shown to be the case in college-age adults (Wilmore and Behnke, 1969, 1970; Katch and McArdle, 1973). Further ~nvestigations are needed to test the validity of the equations developed to other populations of children.

Acknowledgments This research was conducted in co-operation with the Physical Fitness Research Laboratory, Department of Physical Education, University of Illinois. We wish to express appreciation to the staff for their contribution to the study.

References Alien, T. H., Anderson, E. C., and Langham, W. H. (1960). Total body potassium and gross body composition in relation to age. Journal of Gerontology, 15, 348-357. Allen, T. H., Peng, M. T., Chen, K. P., Huang, T. F., Chang, C., and Fang, H. S. (1956). Prediction of total adiposity from skinfolds and the curvilinear relationship between external and internal adiposity. Metabolism, 5, 346-352. Boddy, K., King, P. C., Womersley,J., and Durnin, J. V. (3. A. (1973). Body potassium and fat-free mass. Clinical Science, 44, 621-625. Boileau, R. A., Massey, B. H., and Misner, J. E. (1973). Body composition changes in adult men during selected weight training and jogging programs. Research Quarterly, 44, 158-168. Brozek, J., Grande, F., Anderson, J. T., and Keys, A. (1963). Densitometric analysis of body composition: Revision of some quantitative assumptions. Annals of New York Academy of Science, 110, 113-140. Carter, J. E. L. (1972). The Heath-Carter somatotype method. San Diego, California: Department of Physical Education, San Diego State College: Cheek, D. B. (1968). Human Growth: Body composition, cell growth, energy and intelligence. Philadelphia: Lea and Febiger. Cureton, K. H., Boileau, R. A., and Lohman, T. (3. (1975). A comparison of densitometric, potassium-40 and skinfold estimates of body composition in prepubescent boys. Human Biology, 47, 321-336. Flynn, M. A., Woodruff, C., Clark, J., and Chase, (3. (1972). Total body potassium in normal children. Pediatric Research, 6, 239-245. Forbes, (3. B. (1972). Growth of the lean body mass in man. Growth, 36, 325-338. Forbes, G. B., and Amirhakimi, G. H. (1970). Skinfold thickness and body fat in children. Human Biology, 42, 401-418. Forbes, (3. B., Schultz, F., Cafarelli, C., and Amirhakimi, G. H. (1968). Effects of body size on potassium-40 measurement in the whole body counter (tilt-chair technique). Health Physics, 15, 435-442. Forbes, (3. B., and Hursh, J. B. (1963). Age and sex trends in lean body mass calculated from K 4° measurements: with a note on the theoretical basis for the procedure. Annals of New York Academy of Science, 110, 255-263. Friis-Hansen, B. (1961). Body-water compartments in children: Changes during growth and related changes in body composition. Pediatrics, 28, 169-181.

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Heald, F. P., Hunt, E. E., Jr., Schwartz, R., Cook, C. D., Elliot, O., and Vajda, B. (1963). Measures of body fat and hydration in adolescent boys. Pediatrics, 31, 226-239. Katch, F. I., and McArdle, W. (1973). Prediction of body density from simple anthropometric measurements in college-age men and women. Human Biology, 45, 445454. Lohman, T. G., Boileau, R. A., and Massey, B. H. 0975). Prediction of lean body mass in young boys from skinfold thickness and body weight. Human Biology, 47, 245 262. Lohman, T. G. (1971). Biological variation in body composition. Journal of Animal Science, 32, 647 653. Michael, E. D., and Katch, F. I. (1968). Prediction of body density from skinfold and girth measurements of 17-year-old boys. Journal of Applied Physiology, 25, 747-750. National Center for Health Statistics. (1972). Skinfolds in 6 to 11 year old children, United States. Vital and Health Statistics. PHS Pub. No. 73-1602, Series 11, No. 120, Public Health Service. Washington, D.C. : U.S. Government Printing Office. National Center for Health Statistics. (1973). Selected body measurements of children, 6-11 years, United States. Vital and Health Statistics. PHS Pub. No. 73-1602, Series 11, No. 123, Public Health Service. Novak, L. P. (1966). Total body water and solids in six-to-seven-year-old children: Differences between sexes. Pediatrics, 38, 483-489. Oberhausen, E., Burmeister, W., and Huycke, E. J. (1965). Das Wachstum des Kaliumbestandes im Menschen gemessen mit dem Ganzkorperzahler. Ann. Paediat. 205, 381-400. Parizkova, J. (1961 a). Age trends in fat in normal and obese children. Journal of Applied Physiology, 61, 173-174. Parizkova, J. (1961 b). Total body fat and skinfold thickness in children. Metabolism, 10, 794-807. Siri, W. E. (1961). Body composition from fluid spaces and density: Analysis of methods. In Techniques for Measuring Body Composition, ed. Brozek, J. and Henschel, A., Washington, D.C.: National Academy of Sciences. Steinkamp, R. C., Cohen, N. L., Siri, W. E., Sargen, T. W., and Walsh, H. E. (1965). Measures of body fat and related factors in normal adults. Journal of Chronic Diseases, 18, 1279-1288. Twardock, A. R., Lohman, T. G., Smith, G. S., and Breidenstein, B. C. (1966). The Illinois animal science counter: performance characteristics and animal radioactivity measurement procedures. Journal of Animal Science, 25, 1209-1217. Wilmore, J. H., and Behnke, A. R. (1969). An anthropometric estimation of body density and lean body weight in young men. Journal of Applied Physiology, 27, 25-31. Wilmore, J. H., and Behnke, A. R. 0970). An anthropometric estimate of body density and lean body weight in young women. American Journal of Clinical Nutrition, 23, 267-274. Young, C. M., Sipin, S. S., and Roe, D. A. (1968 a). I. Density and skinfold measurements. Body composition of preadolescent and adolescent girls. Journal of the American Dietetic Association, 53, 25-31. Young, C. M., Bogan, A. D., Roe, D. A., and Lutwak, L. (1968b). Body composition of pre-adolescent and adolescent girls. IV. Body water and creatinine excretion. Journal of" the American Dietetic Association, 53, 579-587. Address correspondence to: M. H. Slaughter, 306 Huff Gymnasium, University of Illinois at Urbana-Champaign, Champaign, Illinois, 61820, U.S.A. Zusammenfassung. Diese Arbeit wurde geplant, um die Berechenbarkeit der fettfreien KSrpermasse (LBM) aufgrund von Mal3en nach der 4°K-GesamtkSrper-Spektrometrie Hautschichtdicken, Umf~inge und Knochenbreiten bei 7- bis 12-J~hrigen zu vergleichen. Die MeBstellen ftir die Hautschichtdicken waren Rficken, Oberarm, Seite, Taille, Bauch und Wade; fiir die Umffinge Unterarm, Oberarm (gebeugt), Handgelenk, Hf~fte, Wade und Brust (ausgeatmet); ffir die Knochenbreiten Handgelenk, Knie, Ful3gelenk, Ellbogen, Schulter und Htifte. Bei einer Gruppe von 163 Knaben bestimmten 3 Hautschichtdicken und das K6rpergewicht 89,7% der Variation der LBM, 2 Umf~inge, die KSrperhShe und das Gewicht 87,2% und 2 Knochenbreiten, die K6rperh6he und das Gewicht 87,4%. Bei Kombination aller MaBe in eine Analyse ergaben sich ftinf Wesentliche Variablen: K6rpergewicht, Hautschichtdicke an Seite und Magen und O b e r a r m - u n d Brustumfang; der resultierende Determinationskoeffizient betrug 90,6%, nur geringftigig hSher als bei KSrpergewicht und 3 Hautschichtdicken. Die wesentlichen Variablen der kombinierten Analyse wurden dann benutzt, um LBM bei ffinf getrennten Altersgruppen bei Knaben und einer Stichprobe von 44 M~idchen zu berechnen. Im allgemeinen beeinflul3ten KiSrpergewicht, Oberarm- und Brustumfang die LBM positiv und Seitenund Bauch-Hautschichtdicken negativ. Die Regressionskoeffizienten ffir jede MeBstelle waren in den Altersgruppen nicht signifikant unterschieden. LBM kann mit betr~ichtlichem Erfolg gesch~itzt werden aus Hautschichtdicken, Umf~ingen oder Knochenbreiten, wie dies auch for Erwachsene im Studentenalter gezeigt werden konnte.

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R6sum6. Cette 6tude a 6t6 conque de faqon 5. comparer le pouvoir de pr6diction de la masse corporelle maigre (LBM), telle que mesurde par spectrom6trie du 4°K du corps entier, 5. partir de plis cutands, de p6rim~tres et de largeurs osseuses chez des enfants de 7 ~t 12 arts. Les plis cutan6s ont 6t6 pris au dos, au bras, au flanc, b. la taille, 5. l'abdomen et au mollet; les p6rim~tres 6taient ceux de l'avant-bras, du bras (fl6chi), du poignet, du mollet et de la poitrine (en expiration); les largeurs osseuses comprenaient le poignet, le genou, la cheville, le coude, les 6paules et les hanches. Dans un groupe de 163 garqons, trois plis cutan6es et le poids assumaient 89,7% de la variation de la LBM, et deux largeurs osseuses, la taille et le poids assumaient 87,4% de la variation de la LBM. La combinaison de routes les variables mesur6s dans une m6me analyse fournit cinq variables significatives: le poids, le pli cutan6 du flanc, le pli cutan6 de l'abdomen, le pdrim~tre de l'avant-bras et le pdrim~tre thoracique avec un coefficient de determination de 90,6%, seulement un peu sup6rieur qu'avec le poids et trois plis cutan6s. Les variables significatives de l'analyse combin6e ont 6t6 ensuite employ6es pour pr6dire la LBM dans cinq groupes d'~.ge de garqons et un 6chantillon de 44 filles. En g6n6ral, le poids et les p6rim6tres de l'avantbras et du thorax contribuaient positivement h la LBM tandis que les plis cutan6s du flanc et de l'abdomen contribuaient n6gativement. Les coefficients de r6gression pour chaque site ne diff6~aient pas significativement entre les groupes d'~ge. La LBM peut 6tre estim6e chez l'enfant ~t partii" de plis cutan6s, de p6rim6tres ou de largeurs osseuses avec un succ~s consid6rable, comme cela s'est montr6 6tre le cas chez des adultes de l'~tge de coll6giens.