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Old 04-22-10, 09:27 AM   #1
FlashBazbo
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Body Fat Percentage: What's going on?

I measure my weight, bodyfat, water % twice a day on a Tanita digital scale -- one of those most recommended on the BF. Like most cyclists, my weight tends to increase by a few pounds in the off-season and I get down to racing weight during the season. Over the course of the year, my weight may fluctuate as much as ten pounds.

But my bodyfat and water% don't fluctuate much at all.

This year, I have lost seven pounds -- at a rate of less than one pound per week -- but my bodyfat and water numbers are still pretty close to the same. I suspect my power is up quite a bit because my speed for a given heart rate is up (but I don't have a power meter to verify it).

What's going on? Am I doing something wrong with my training/nutrition? (Or are these scales just not that accurate?)
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Old 04-22-10, 11:22 AM   #2
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Well, I dunno. For relative body fat just a caliper skin fold test works pretty well. Shoot you can do it old pinch of a skin fold on you tummy on the lateral side just above the upper crest of the pelvis. If that is getting thinner, you probably have less body fat. Or you can buy a pair of calipers and do the 4 point skin fold test - a fold on the top of the quad (thigh), a fold on the back below the shoulder blade, a fold above the crest of the pelvis and a fold on the triceps.

Measuring body fat is pretty problematic and every test has problems. The water buoyancy test is awfully sensitive to how much air you have in your lungs, skin fold can be tricky and the impedence methods you mentioned have their problems. The only method I know of that is accurate is totally destructive to the subject.

If your flabby areas have shrunk, you are almost certainly leaner.
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Old 04-23-10, 10:25 AM   #3
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The impedence measurements can vary by 2-3% and they are very sensitive to hydration status.
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Old 04-23-10, 10:33 AM   #4
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Well, I dunno. For relative body fat just a caliper skin fold test works pretty well. Shoot you can do it old pinch of a skin fold on you tummy on the lateral side just above the upper crest of the pelvis. If that is getting thinner, you probably have less body fat. Or you can buy a pair of calipers and do the 4 point skin fold test - a fold on the top of the quad (thigh), a fold on the back below the shoulder blade, a fold above the crest of the pelvis and a fold on the triceps.

Measuring body fat is pretty problematic and every test has problems. The water buoyancy test is awfully sensitive to how much air you have in your lungs, skin fold can be tricky and the impedence methods you mentioned have their problems. The only method I know of that is accurate is totally destructive to the subject.

If your flabby areas have shrunk, you are almost certainly leaner.
GNC sells a plastic skin fold caliper for less than $15 if you really want to determine %
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Old 04-23-10, 10:41 AM   #5
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(Or are these scales just not that accurate?)
Bingo.
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Old 04-23-10, 11:09 AM   #6
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In addition to what other said, if you have lost weight and your BF% is the same, that means you have lost fat. e.g If you started at 175 lbs & 10% bf, you had 17.5 lbs fat. If you lost 7 lbs & still have 10% bf, you now have 16.8 lbs fat (10% 168). Probably not the answer you want because it would mean the rest of the weight loss is muscle weight. This assumes the numbers are accurate, which, as has been said, is questionable. I find the fit of my clothes & which hole in my belt I'm using tells me more than calipers. Plus trying to test bf% 2x a day is too much. Test every 2 weeks.
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Old 04-23-10, 11:36 AM   #7
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Plus trying to test bf% 2x a day is too much. Test every 2 weeks.
I have never figured out how fewer data points could be better.

The Tanita scale takes only a couple of seconds to do its thing. I never figured it to be deadly accurate -- but DID figure that it would give an idea of trends over time.

And, Chinarider, you clearly understand my concern. If these readings mean I'm losing muscle mass, I need to do something differently.

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Old 04-23-10, 02:12 PM   #8
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I have never figured out how fewer data points could be better.

The Tanita scale takes only a couple of seconds to do its thing. I never figured it to be deadly accurate -- big DID figure that it would give an idea of trends over time.

And, Chinarider, you clearly understand my concern. If these readings mean I'm losing muscle mass, I need to do something differently.
The problem with testing 2x a day is that there is so much normal variation, that hour to hour or day to day changes are meaningless (that applies to weight also). It is the long term trend that matters.

As far as whether the readings mean you're losing muscle mass, the mirror may be the best indicator of that. If you're on a severely calorie restricted diet and doing a lot of cardio, you could be. If you're eating enough and doing some strength work, you may have lost a little, but I doubt enough to approach 7 lbs. If you did, you'd be able to see it. Sometimes we get too high tech. I think a mirror, tape measure and your belt can tell you more than a BF% scale & calipers.
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Old 04-23-10, 03:04 PM   #9
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What's going on? Am I doing something wrong with my training/nutrition? (Or are these scales just not that accurate?)
Those scales are BS
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Old 04-26-10, 05:10 AM   #10
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After having done some additional research (and paying closer attention to my urine -- TMI), it appears that I've been burning a good deal of protein/muscle in my workouts. The problem? Too little carbohydrate before/during/after workouts. I need to shift protein calories to carbohydrate calories and eat them closer in time and before my workouts.

I'll try to make the shift and see how it goes.

It's entirely possible that I've been staying close to bodyfat proportional on my way down in weight. My heart is more fit, but it's kind of discouraging that I've likely been consuming muscle.
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