Introduction
Typically, a simple
and reasonably accurate method of assessing changes in body composition
have included skin fold measurements. The seven point skin fold
method is used by many exercise consultants who seek a relatively
accurate, simple, and inexpensive measurement of body composition.
Clients who engage in exercise or dietary manipulation can receive
immediate feedback so timely modifications can be made to their
program. Dependent upon the expected rate of change in body composition,
clients can be measured every month or so. If the rate of change
is expected to be rapid, as with dieters, body composition can
be sampled more frequently, e.g.. weekly. Caution should be exercised
in interpreting data when tests are performed frequently, since
measurement error, or variability may exceed an actual change
in body composition. In which case, the general trend of the
results can be noted or additional tests can supplement body
composition data, such as waist circumference measurement or
other girths. When performed as recommended, the whole process
of the measuring body composition with the seven point skin fold
method and calculating the absolute amount of fat and lean body
weight can be time consuming, especially with many clients. In
this study, in effort to save time and reduce test variability,
two other tests that predict body composition were compared with
seven point skin fold method and are discussed.
The subcutaneous fat comprises of approximately one half the
total fat in the body. By the end of World War I, anthropologists
realized the feasibility of measuring subcutaneous fat. By 1930,
researchers developed an instrument to measure selected sites
on the body with relative accuracy. (Katch and McArdle, 1983)
The thickness of a double layer of skin and
the fat beneath it is measured with the special caliber that
exerts a constant tension on the site. Skinfolds must be taken
at precise standard locations if the results are to be reliable
and used for comparative purposes. (Katch and McArdle, 1983)
Lohman and Roche made recommendations on techniques to derive
skin fold readings based upon a variety of methods used in the
literature throughout the years. Reliability and validity of
the many sites were reported in predicting body density. (Lohman
and Roche, 1998)
Katch and McArdle express that population specific equations
only accurately predict body fat (BF) for a subject that is similar
to the population that the formula was derived from. According
to Katch and McArdle, the major drawback with the skinfold technique
lies in extensive expertise, one must have in taking readings
accurately and with consistency. Katch and McArdle claim that
with research purposes, the investigators usually has already
performed several thousand skin folds. (Katch and McArdle, 1993)
Body Composition Formulas
Jackson and Pollock describe certain limitations associated
with population specific formulas and linear regression models
in attempting to estimate BF from skin fold measurements. They
noted that with a sample of men of different age, the slopes
of the regression lines were the same, but the intercepts were
significantly different. In addition, the slopes of the regression
lines were not parallel between young adult men and extremely
lean world class runners. Furthermore, research has shown a curvilinear
relationship exists between skin fold measurements and body density
(BD). Jackson and Pollock proposed that this nonlinear relationship
may be the reason for the differences in slopes and intercepts.
They develop several formulas based upon a quadratic relation
and the function of age. (Jackson and Pollock, 1978)
The following formula is one of Jackson and Pollock's that
has been used widely in research:
 BD= 1.11200000  0.00043499(X) + 0.00000055(X)(X)  0.00028826
(A)

 X = Sum of chest, axilla, triceps, subscapular, abdomen,
suprailium, and thigh skin folds (mm).
 A = Age in years.
This formula had a correlation of .915 when compared to hydrostatic
weighing to estimate body density. The standard error of estimate
was .008 expressed in body density and a standard error of estimate
of 3.5 when expressed in % BF using the following equation by
Siri (1961):
 % Fat = [(4.95/BD)  4.5] 100
The absolute amount of fat and lean body weight (LBW) can
be calculated using the body weight of the individual.
Behnke and Wilmore have developed several formulas to estimate
BD and LBW based upon anthropometrics they obtained from 133
college age men. The anthropometrics used in the predictive formulas
included skinfolds, diameters, and circumferences. The authors
noted that the correlation coefficients for estimating LBW was
higher that for estimating BD, although the standard error of
estimate was higher in estimating lean body weight. It seems,
though, an oversight was made in their comparison of the standard
error of estimates of the two different types of formulas. The
formulas that were used to estimate LBW were expressed in kilograms,
whereas the formulas used to estimate BD were expressed as grams
per milliliter. A direct comparison needs to be made to compare
the standard error of estimate for the two different types of
formulas. They did, though, caution the use of these formulas
until further studies could either confirm or refute their validity,
since the population used to derive data was of a specific population.
(Behnke and Wilmore, 1969)
The following formula offered by Behnke and Wilmore seems
to offer some savings of time in the way of data collection and
calculation:
 LBW= 10.260 + 0.7927(wt)  0.3676(s)

 wt = Body weight (Kg)
 s = Abdominal skinfold (mm)
This formula had a correlation of .931 when compared with
hydrostatic weighing. The standard error of estimate was 2.977
expressed kilograms. It must be noted, though, that misleading
comparisons may be made in comparing the correlation of data
derived from formulas to that of hydrostatic weighing in different
studies. This is because hydrostatic weighing in itself has a
standard error of estimate.
Katch and McArdle recognize that circumferences may be taken
with ease, achieving accuracy with little practice. They recommend
to record measurements in centimeters for added precision. In
addition, an average of two measurements at the same site was
advised. They also noted that pulling the tape too tight would
compress the underlining soft tissue making the measurement inaccurately
smaller. (Katch and McArdle, 1983)
A simple formula using an abdominal circumference is offered
by Behnke and Wilmore:
 LBW= 44.636 + 1.0817(wt)  0.7396(c)

 wt = Body weight (Kg)
 c = Circumferences of Umbilicus Abdomen (cm)
This formula had a correlation of .938 when compared with
hydrostatic weighing. The standard error of estimate was 2.815
expressed in kilograms.
Methods, Data, and Statistical
Analysis
To examine the new formulas explored above, seven male subjects
were included for testing. All subject desire LBW gains and a
reduction of BF. All but one subject engaged in weight training
and supported a larger than average musculature. The anthropometrics
necessary to complete all three formulas discussed above were
collected and calculated. Only two subjects have more than one
set of data.
Subjects 
Percent Body Fat 
Seven Site 
Abdominal Skinfold 
Abdominal Circumference 
WY 
22.68 
25.17 
17.18 

24.62 
19.55 
11.65 

24.62 
29.02 
18.57 

10.31 
15.62 
12.78 

8.94 
15.50 
12.48 

6.93 
13.81 
11.52 
AR 
14.92 
19.89 
15.47 
BM 
7.93 
14.10 
12.77 
CT 
25.17 
28.91 
19.52 

22.55 
27.50 
18.08 
AF 
23.6 
30.50 
21.50 
B 
15.59 
21.60 
19.89 
KM 
7.73 
14.58 
13.78 
The data were compiled and analyzed using both Ttest (LSD)
and Tukey's Studentized Range (HSD). These tests were used to
determine the relationship between all three formulas. Both tests
indicated a significant difference between the single abdomen
skin fold and the other two methods. No significant difference
was found between the seven site skin fold method and the abdominal
circumference method.
Ttest
 Critical Value of T= 2.04
 Least Significant Difference= 3.8147
Tukey's Studentized Range Test
 Critical Value of Studentized Range= 3.486
 Minimum Significant Difference= 4.6047
Ttest & Tukey's Studentized
Range Test
 Alpha= 0.05
 df= 30
 MSE=22.67761
* Means with same letter are not significantly different.
Method 
T Grouping 
Tukey 
Mean 
N 
AB SF 
A 
A 
21.212 
13 
7 Site 
B 
B 
16.583 
13 
AB CR 
B 
B 
16.168 
13 
Conclusions
A closer analysis of individual data shows a general trend.
It seems that the abdominal skin fold method overestimates BF
when compared to the seven point method. The abdominal circumference
method, on the other hand, underestimates BF when the subject
is above average BF according to the seven site method. This
"cut off" seemed to be somewhere within 15.59 % BF
and 22.68 % BF. When BF was 15.59 % and lower, according to the
seven site method, the abdominal circumference method overestimated
BF. It can be seen how a greater than normal musculature of the
midsection could falsely decrease the LBW calculation, therefore
increasing the % BF calculation. The overestimation of BF on
some calculations and an underestimation of BF on others is most
likely responsible for the seemingly high correlation with the
seven point method shown above. Despite the ambiguity of the
abdominal circumference method, it was thought to be more reliable
than the seven site skinfold with those individuals above 22.68
% BF. It is known that more obese individuals pose a greater
threat to the reliability of skinfold measurements. (Lohman and
Roche)
It became evident only after the first few calculations that
the trial formulas were not applicable to the population tested
in this study. As mentioned before, Behnke and Wilmore's formula's
were derived from average age college students. The subjects
used in this study were, probably at best, average age college
students with excessive muscle mass.
Bibliography
Behnke, A.R., Wilmore, J.H. An anthropometric estimation of
body density and lean body weight in young men. Journal of
Applied Physiology. 27: 2531, 1969.
Jackson, A.S., Pollock, M.L. Generalized equations for predicting
body density. British Journal of Nutrition. 40: 497504,
1978.
Katch, F.I., McArdle, W.D., Nutrition, Weight Control,
and Exercise. Lea & Febiger: Philadelphia. PA, 1983.
Lohman, T.G., Roche, A.F. & Martorell, R. (eds.). Anthropometric
Standardization Reference Manual. Human Kinetics Books: Champaign,
IL ISBN O873221214. 1998.

