Estimating bodyfat: RFM

[quark]

There's a new formula for estimating bodyfat, relative fat mass, or RFM:

MEN: 64 – (20 x height/waist circumference) = RFM

WOMEN: 76 – (20 x height/waist circumference) = RFM

https://www.sciencealert.com/new-accura ... mass-index

What do you think?

[michael]

That formula will punish the muscular.

Imagine you gain 20 pounds of muscle with no waist increase. The formula doesn't think your body fat changed.

[TimK]

Sweet, I just need to get my waist measurement down to 26" and I'll be 10% bodyfat. Here come the shredz!

ETA: I'm 5'11. According to Google, Frank Zane was 5'9" and had a 29" waist, which works out to 16.4% BF... so yeah. This might have some clinical validity as a screening tool (like BMI) but it seems pretty worthless to anyone that's in to fitness/lifting and want's to estimate their BF%.

UNLESS the poorly written article has misled me and the number you get is not supposed to equal your BF%.

[mbasic]

I'm over 27% ... fuck!

[michael]

I'm sure the living skeletons at r/fitness will love it.

[quark]

That formula will punish the muscular.

Imagine you gain 20 pounds of muscle with no waist increase. The formula doesn't think your body fat changed.

The Navy method is based on the difference between waist and neck sizes, so if you gain 20 pounds of muscles with no waist or neck change, it doesn't think your body fat changed either.

Both RFM and Navy are better than BMI, which is just height and weight, so 20 pounds of muscle is the same as 20 pounds of fat.

Are there any formulas you prefer?

[michael]

That formula will punish the muscular.

Imagine you gain 20 pounds of muscle with no waist increase. The formula doesn't think your body fat changed.

The Navy method is based on the difference between waist and neck sizes, so if you gain 20 pounds of muscles with no waist or neck change, it doesn't think your body fat changed either.

Both RFM and Navy are better than BMI, which is just height and weight, so 20 pounds of muscle is the same as 20 pounds of fat.

Are there any formulas you prefer?

I like the YMCA formula best. Modified YMCA is better for lifters.

[michael]

I have a Skulpt which actually seems quite accurate.

[quark]

I like the YMCA formula best. Modified YMCA is better for lifters.

Men:


Where A is weight and B is waist

Women:


A) Total Body Weight, B) Wrist Circumference, C) Waist (at navel), D) Hips (at the fullest point), and E) Forearm Circumference.

All in inches and pounds.

[JohnHelton]

RFM doesn't seem to work for me. 8% higher than both Navy and YMCA. (Both Navy and YMCA are higher for me than a water displacement test, but they are close.) Height and waist size are not enough variables. If you are a pencil neck with a gut and are 6'0" tall, then you will have the same BF estimate as a jacked dude with the same size waist (thick with muscles) that is also 6'0". Navy compensates by looking at neck size. YMCA compensate by incorporating body weight.

[TimK]

RFM doesn't seem to work for me. 8% higher than both Navy and YMCA. (Both Navy and YMCA are higher for me than a water displacement test, but they are close.) Height and waist size are not enough variables. If you are a pencil neck with a gut and are 6'0" tall, then you will have the same BF estimate as a jacked dude with the same size waist (thick with muscles) that is also 6'0". Navy compensates by looking at neck size. YMCA compensate by incorporating body weight.

It seems like a much better formula would be possible utilizing a combination of height, weight, neck size, and waist measurement (why not hips too while we're at it). I wonder why someone hasn't figured this out yet.

[JohnHelton]

I am actually blow away by how close the estimates between YMCA and Navy are. I've have a bunch of historical data and can run the results against each other. They are always within 1% of each other for me. Thus, I'll choose YMCA going forward since I don't have to worry about neck measurements. The fewer measurements, the better.

[quark]

For me, ymca and rfm are the same, while navy is about 5 percentage points lower.

There has to be some research into the various methods. If memory serves, there's a thread here in twhich someone reported on their small scale test for uni.

Anyone use or like caliper measurements?

[TimK]

I don't put stock in any of these personally. I just track my BW and use waist measurement changes as a proxy for BF% changes. If my waist measurement is the same as it was some time in the past but I'm significantly heavier then I take that as evidence that I have gained muscle. If I'm the same weight but smaller waist, I must have a lower BF%. And ultimately looking in the mirror tells me what I really want to know better than a calculated number. I've thought about getting a DEXA scan done but only if I get pretty lean first, and then only do it again like once a year or something like that to measure long term progress.

[quark]

@TimK That sounds very sensible.

I track BW and waist. My current general plan: If waist size is reasonable, increase BW slowly. If waist size becomes too large (measured or visible), decrease BW until it's reasonable again.

Nonetheless, it would be interesting to know BF%, even if I'm not sure what I'd do with the information.

[JohnHelton]

BF% numbers are all wrong, no matter the source. Using the same technique is more important so that you can compare values on a relative basis. I understand that DEXA will give you higher values. Of course that is fine if you then always use DEXA as your measuring stick. I'm fine with my imprecise waist measurements. I still can't see my abs. If I ever get to that point...then I still won't know my actual body fat. I will only know that I can now see my abs. Which would be pretty cool even if it doesn't last.

[michael]

I am actually blow away by how close the estimates between YMCA and Navy are. I've have a bunch of historical data and can run the results against each other. They are always within 1% of each other for me. Thus, I'll choose YMCA going forward since I don't have to worry about neck measurements. The fewer measurements, the better.

Exactly my experience.

[TimK]

BF% numbers are all wrong, no matter the source. Using the same technique is more important so that you can compare values on a relative basis. I understand that DEXA will give you higher values. Of course that is fine if you then always use DEXA as your measuring stick. I'm fine with my imprecise waist measurements. I still can't see my abs. If I ever get to that point...then I still won't know my actual body fat. I will only know that I can now see my abs. Which would be pretty cool even if it doesn't last.

Right, that's why I just track waist measurement & BW. If I take those and plug them into a formula, it doesn't really give me any new or better information.

[michael]

Right, that's why I just track waist measurement & BW. If I take those and plug them into a formula, it doesn't really give me any new or better information.

I think the formula is useful.

It gives you a better idea of how much fat/muscle you are losing/gaining on a cut/bulk.

[TimK]

Right, that's why I just track waist measurement & BW. If I take those and plug them into a formula, it doesn't really give me any new or better information.

I think the formula is useful.

It gives you a better idea of how much fat/muscle you are losing/gaining on a cut/bulk.

So does comparing the changes in your weight and waist measurement though. Or looking in the mirror/taking progress photos. I don't know, it just seems like the formulas are just taking a couple of rough-but-useful measurements and converting them into a number that gives a false sense of precision. I guess if you want to boil everything down to a single number, it's fine.