BF% Scales

[cheesesteak]

I only have access to one at the gym. It's the kind you stand on, enter your sex and age, then squeeze handles for 5 seconds and it does your reading.

When I first joined I was 241lbs, 31.1% bf. Recently I was 216lbs, 27.7% bf.

Too me that seems inaccurate for that much weight loss to only yield 4% bf loss.

Is this machine just bunk? I don't have access to anything else.

[Ritch]

Those are the worst! I knew a guy who was skinny fat and tested below 10%...

[cheesesteak]

Phew! I guess after I lose enough weight to be satisfied I'll put up some pics and let you guys guesstimate. I just want to get down low enough where I can start to bulk. I figure with 2lbs per week (hopefully) in 18 weeks I should be good.

[steve_d]

I don't know how they work, but they are completely useless. I once tested at 16% on the scale, then I drank 2 litres of water, and then it jumped to 20%.

[agingtechie]

My bath room scale has the body fat thing in it. I find that it is very dependent on body hydration. The scale uses an electric current to measure your body's electrical resistance and guesses at your body fat based on your weight. I find that my scale is only good for weight in the morning and BF% at night when I am more hydrated.

Do you take the reading before or after your workout? If you do a hard and sweaty work out your body will be less hydrated and you will get a higher reading.

I think it is better to go with a fat caliper.

On the plus side the Gym scale is telling you that you are going in the right direction.

[Memo]

I tried one in a gym once, that print your goal.

The thing said 5"5 150lbs bf%8 goal: you should loose 16 pound

I was mindblown

[Bigtred]

Those scales are pre adjusted for the AVERAGE PERSON, not someone who's training. Chances are the BF% was wrong in the first place and now that you've put on a bit more muscle mass, it's even more wrong

[nitrous]

ya if they cant come up with something thats accurate they shouldnt allow it to be sold in the market

[baza]

My bath room scale has the body fat thing in it. I find that it is very dependent on body hydration. The scale uses an electric current to measure your body's electrical resistance and guesses at your body fat based on your weight. I find that my scale is only good for weight in the morning and BF% at night when I am more hydrated.

Bingo.

[gsxr750]

^^ Ditto. Same thing, BF % fluctuates over 5-10% depending on time of day.

Invest in some calipers, they're cheap and accurate

[Doryphorus]

There are actually pretty major issues with body composition calculations in general... First off they don't account for different tissue/bone density --> There was actually a study published in 1982 where the author tested several members of a professional football team and they came out with negative bodyfat, likely due to increased bone density related to the amount of weight bearing exercise done by football players compared to "average joe". Unfortunately, all I've got saved in my notes is the table in question and the author/year (Adams et al., 1982) but no title.

Other than dissection, there are no direct methods of measuring body composition. There are only indirect methods which are split into 2 groups:

Type II indirect: Based on quantitative assumptions such as the density of fat and fat free mass, as well as the assumption that all fat free mass has a water content of 73.2%, and that the residual volume of air left in a person's lungs after a maximal exhalation is the same in every case, as is the volume of gas/mass of contents trapped in their gastrointestinal tract (used in densitometry, where the subject exhales maximally, submerges themselves fully and then is weighed and the volume of water displaced is measured). Examples of this type include 40K counting (counts levels of a potassium isotope in the body to determine fat free mass --> the assumption that the isotope is distributed evenly throughout fat free mass is made), densitometry (eg. Underwater weighing), and total body water calculations.

Type III doubly indirect: These methods are calibrated against a Type II method, even though the Type II methods have never been proven accurate, and have obviously flaws in their reasoning. The 2 most commonly used examples of these methods are Bioelectric Impedence Analysis(BF scales), and skinfold measurements. In fact, as of 1991, none of the methods currently used to calculate body composition had been tested in humans, and only 8 human cadavers had ever been dissected to directly determine body composition, tissue density etc. The results were never compared to indirect (non-dissection) methods used on living subjects.

For the scales like you described, the first issue is WHAT is being measured. When you hold the handles, a small current travels from one handle through your UPPER body to the other handle. When you stand on the scale, a current passes from the sensor on one foot through your LOWER body to the sensor on the other foot. There are whole body BIA machines, where an electrode is placed on the hand and the foot, but even still assumptions such as uniform tissue density and cross sectional area (try flexing your pecs/arms while you're holding it, or lift the thing above your head instead of holding it in front of you when you do it and see what happens), and uniform hydration levels (why BF% fluctuates throughout the day) are made. Basically, the body is broken down and examined like a bunch of cylinders placed on top of each other to make a body, one for each segment (foot, lower leg, thigh, torso etc)

In the case of skinfold measurements, assumptions are made such as constant skinfold patterning/adipose tissue deposits throughout the body --> for example, a tendency for adipose tissue to shift from the limbs to the trunk, presence of secondary sexual adipose tissue on the upper arms, hips and thighs of females. Also, constant skinfold compressibility is assumed when it is known that there are differences in skin thickness, tension/elasticity, and adipose tissue composition among individuals. Constant tissue density is also assumed, such as assuming the density of fat free mass is 1.100g/mL even though individuals were measured to have densities of 1.057g/mL for a subject with osteoporosis, and 1.189g/mL for a subject with osteosclerosis (higher than normal bone density). It has also been shown that a mere 6 weeks of bed rest can cause a 2% loss in bone mineral. Another assumption is that there is a constant ratio of external:internal adipose tissue, even though it has been shown to vary with levels of obesity, as well as in extremely lean individuals, and has been shown to decline with age. Lastly, there is an assumption that there is a constant fat content of adipose tissue. In skinfold measurements, what is actually being measured is adipose tissue, not fat. Adipose tissue does contain fat, held in adipocytes, however the size and number of adipocytes varies between individuals (I’m sure some of you have heard that when you develop new fat cells they’re with you for life, and when you become lean they just shrivel up. This is what I’m referring to.).
To date, it is accepted that there is a +/- 3-5% BF error inherent in skinfold bodyfat measurements. The important thing to notice about this statement is the %BF. This means that if you are measured to 10% BF +/- 5% BF, it’s not 9.5-10.5%BF, it’s 5-15% body fat.

Although the assumptions I talked about may seem trivial, consider this: A subject has a whole body density of 1.07g/mL, and the estimated body fat is 12.7%. If his fat free density is actually 1.12g/mL rather than the assumed 1.100g/mL, then his body fat become 19.1% by the same equation. Similarly, if his fat free density is only 1.08g/mL instead of 1.100g/mL, his calculated body fat is 4.7%.

I know the few of you who made it this far into my rambling will be skeptical about how old the studies are I’m referring to. However, next time you go get your skinfolds measured, ask which formula they are using. Likely it’ll be the Siri equation (1956), the Brozek (1963), the Yuhasz (1974) or the Durnin & Womersley (1974) which are all much older than the studies used.
For anyone interested, PM me and I’ll send you .pdf copies of the studies.

For everyone else, here’s the titles/authors. Not a proper bibliography I know, but it’s almost midnight and I’m not writing a proper paper.

Heymsfield et al., 1997. HUMAN BODY COMPOSITION: Advances in Models and Methods

Ward, 2004. Anthropometric Prediction of Percentage Body Fat

Martin and Drinkwater, 1991. Variability in the Measures of Body Fat. Assumptions or Technique?

Clarys, Martin and Drinkwater, 1984. Gross Tissue Weights in the Human Body By Cadaver Dissection

[Doryphorus]

Apologies in advance for the length of the reply. I'm a 4th year biomedical physiology/kinesiology major and just happened to have an entire course on exactly this subject last spring, and I figure if I can't use/share what I learn, there's no point in learning it!

[tiramisu]

That said calipers are much better than a kick in the head and bodyfat scales are entirely useless.

[cheesesteak]

Well I guess thinking all this time I had 161lbs of LBM was dumb. ****ing scale, false hope.