Body composition is the only non-performance measurement among the physical fitness components. Body composition is the proportion of fat-free mass to body fat. Fat-free mass is made of the body’s non-fat tissues which include bone, muscle, water, connective tissues, teeth, and organs. A small amount of fat is needed for the body to function properly. This is know as essential fat. In males, this is about 3% to 5% of total body weight. While in women, this is about 8% to 12% of total body weight. Other body fat is stored as adipose tissue, which is under skin and around the viscera.
While most people still like to use weight as a guage for fitness, it is actually the percentage of body fat that most people should pay attention to. Both the ACSM and the NSCA publish recommended norms for body fat percentage. Charts are presented below:
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ACSM Body Composition
Chart (1)
(image from http://healthypoints.info/) |
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| NSCA Body Composition Chart (1) |
We can actually use
these norms to compute ideal body weight or mass from the ideal body fat
percentage. Mcadle, Katch and Katch (2) and Wilmore and Costill (3) present two
approached to computing ideal body mass.
The first step to both approaches is
to get the fat free weight. Before doing that, you have to be able to determine
the amount of body fat you have. The gold standard in getting body fat would be
hydrostatic weighing (2, 3). However, due to the difficulty in finding equipment
needed, the most practical and available would be getting the skinfolds using a
body fat calliper. Most personal trainers and strength and conditioning coaches
will be trained in using this method. There are several skinfold sites that are
used to determine body fat. In addition, which sites to be tested will be the
decision of the trainer. Information on the different sites is available
elsewhere on the web. Once the skinfold sites have been measured, several formulas
are available to derive the %BF. How to take skinfold measurements and
computations is a different subject matter for the future.
Another option is bioelectrical impedance analysis (BIA). Several machines are available on the market that measure body fat, weight, and resting/basal metabolic rate (RMR/BMR). Such machines are easy to use and are available in some gyms. If it’s available in your gym, have one of the trainers or staff take your body fat, weight and RMR.
Once the body composition, or relative body fat, is determined and compared to the charts above, one can now compute ideal body weight. Compute first for the fat-free mass (FFM), which is weight multiplied by the relative body fat. For example, if a person has 28% body fat and weights 75 kgs, calculate first the fat weight:
= 21 kg
= 54 kgs
Another option is bioelectrical impedance analysis (BIA). Several machines are available on the market that measure body fat, weight, and resting/basal metabolic rate (RMR/BMR). Such machines are easy to use and are available in some gyms. If it’s available in your gym, have one of the trainers or staff take your body fat, weight and RMR.
Once the body composition, or relative body fat, is determined and compared to the charts above, one can now compute ideal body weight. Compute first for the fat-free mass (FFM), which is weight multiplied by the relative body fat. For example, if a person has 28% body fat and weights 75 kgs, calculate first the fat weight:
Fat weight = Weight x relative
body fat
= 75 kgs x 28%
Subtract the fat weight from the
weight to get the fat free weight:
Fat Free Weight = Weight
– Fat Weight
= 75kgs – 21kgs
After computing for the FFM, we can
compute for ideal body weight. Let’s start with Mcardle et al’s formula to
compute ideal body weight (2):
If, in the above example, the person
is a female aged 27, we can check the range
of her ideal body fat using the chart used by the NSCA presented above. In this
case, the ideal average body fat range is between 24% and 26%. We can compute
the range of the desirable body mass:
Goal Body Weight with 26% body fat =
54 kgs / (1.00 – 0.26)
= 54 / .74
= 72.97 kgs or 73 kgs
Goal Body Weight with 24% body fat =
54 kgs / (1.00 – 0.24)
= 54 kgs / 0.76
= 71.05 kgs
or 71 kgs
From the above calculations, using
Mcardel, Katch and Katch’s formula, the ideal body weight for the a 27 year-old
female weighing 75 kgs with 28% body fat, is between 71 kgs and 73 kgs.
Another method, and similar in
computation is the one presented by Wilmore and Costill (3). The computation
for fat free weight is the same as above. Let’s use the same example given, 27-year-old
female at 75 kgs with 28% body fat, the computed fat free weight is 54 kgs.
Again, using the NSCA chart, we plug
in the values for her age, 24% and 26% respectively.
Goal
BF% = 26%
Goal fat –free mass = 100% - Goal
BF%
= 100 – 26
= 74%
Goal weight at 26% BF = Current
fat-free weight / Goal fat-free weight
= 54 / 0.74
= 72.97 kgs or 73 kgs
Weight loss goal at 26% BF =
Current body weight – Goal body weight
= 75 kgs – 73 kgs
= 2
kgs
Computing also for the lower BF%, we
have the following computations:
Goal BF% = 24%
Goal fat-free mass = 100% - Goal BF%
= 100 – 24
= 76%
Goal weight at 24% BF = Current
fat-free weight / Goal fat-free weight
= 54 /
0.76
= 71.05 kgs or 71 kgs
Weight loss goal at 24% BF = Current
body weight – Goal body weight
= 75 kgs – 71 kgs
= 3.95 kgs or 4 kgs
Both methods presented above produce
the same figures as shown. Which method to use to compute desirable body weight
will be up to the trainer. Using the
computations allows the trainer to present to their potential clients a more
concrete goal in terms of achieving desirable body weight, along with the ideal
percentage of body fat for their given age and gender.
Bibliography:
- Earle, Roger W. and Thomas R. Baechle “NSCA Essentials of Personal Training” 2004
- Mcardle, William D., Frank I. Katch, and Victor L. Katch “ Exercise Physiology: Nutrition, Energy, and Human Performance 7th edition” 2010
- Wilmore, Jack H. and David L. Costill “Physiology of Sport and Exercise 2nd edition” 1999
