How do body comp scales interpret glycogen?
 

This is just for pure curiosity. I don't think you can do anything with this. But I'll get to that. I have a Withings and it gives weight and % water, % fat, % bone, % muscle.

Alright. A big contributor to day to day weight swing is water and glycogen usage and storage. I'm curious how something like a Withings interprets liver and muscle glycogen. Will that fall under water weight, muscle, or fat. I can rule out bone as bone % stays identical on every reading, as I would hope it to!

I weigh sometimes after a workout. Just notice the % for water doesn't do what I'd expect. I simply rehydrate after workouts as necessary without a scale. So wouldn't change that, just curious.

Mostly they guess. It's not something that can be directly measured. Your weight is about the only thing that it can tell you as result of direct measure. Everything else is a result of some indirect measurement and comparing that to some study of what it was for a group of people that may not be you.

Typically it's accurate to some degree. But leaves lots of room for argument if you are going to compare your results with another.

I have a similar scale. I notice that the day after maybe a 2 hour workout, if I did not adequately replace carbs, my weight the next morning is down by a pound or so. If I do have an after-workout carb drink, my weight doesn't change as much, maybe down by .2. I assume that most of that weight change difference is due to glycogen replacement, i.e. mostly water. My water percent bounces around so much that I confess I haven't paid too much attention to it. I think my muscle percent is more reflective of my glycogen balance.

I only pay close attention to my scale numbers when I weigh myself first thing in the morning. If I weigh myself later in the day, all my numbers are different, especially my muscle number will be way up. Maybe more blood in the muscles increases the scale number? I don't bother weighing myself before and after a workout.

Tell you what . . .I'm doing a somewhat glycogen-depleting workout this morning. I'll weigh myself naked before and after, before my "after" drink, and post the results.

One can't compare one's numbers with anyone else's, but comparing the changes in numbers might be interesting.

I've noticed roughly the same. I was assuming the glycogen was wrapped up in the water %.

I've had some instances of workouts where the fat % drops a solid 1 to 1.5% and the water % goes up by 1 to 1.5% while my bone and muscle isn't too changed. Was just curious about that.

I really just pay attention to the trend line in their app. If that's where I want to be. Making sure fat % and muscle % go the desired directions. Overall weight doesn't bother me too much as I'm not a pro.

I got the scale because of knowing about how water weight can toss your perception, and because from Nov thru Dec I drank a ton of red wine and had a lot of pastries with my coffees. So put on a bit of fat.

I did the workout, though I got interrupted in the morning and had to quit halfway through. I did the other half, which was identical to the first half, in the afternoon. Both were about 45'. Results were that my weight dropped about 1/2 lb. both times - I only drank about 4 oz sports drink each time and was riding at 58° with a box fan. The other numbers changed a little bit between before and after, but between the morning and afternoon reading pairs they either did not change or changed in the opposite direction, so probably just random variation. IOW a null result for your interest. IME though, if glycogen is being broken down, one doesn't pee out the water right away. Don't know why, but the peeing seems to come hours later, at least for me.

I was doing a 16' warmup, a 20' 53 rpm interval at 95% FTP but below AeT, and then a 10' cool down. During the 60% FTP normal cadence cool-down, it was like, "Where'd the chain go? Or is my PM broken?" :) Too bad I didn't get to do them both on the same ride, but this was interesting, too. Tomorrow it's 4 X 6 X 3 105% intervals, working up to 4 X 8.

I think this got it.

I actually weighed my normal mid-later day weight after a ravaging 1:20 on the TT bike on Tuesday. But, my water % on the scale had gone WAY up. Then after a lot of pee that evening and a solid night time pee, the weight during my normal after breakfast weigh in the next morning was down. Water weight % back to normal. But, glycogen not likely restored yet as I am NOT a big breakfast person any longer.

Some yogurt and a black coffee if I'm not riding early in the day. I simply found the "eat now so you don't eat a lot later" did not work for me. If I ate a good breakfast just to go sit at work, I still would eat the same lunch, same dinner, same evening snack with Netflix.

So, unless I'm riding early day I don't do the whole "nice breakfast" any longer. It wound up just being about 300cal a day of "filler".

My bedtime snack is 15g whey protein in water. That's worked surprisingly well. This morning's weigh-in found my weight unchanged, water up, muscle and fat both down from yesterday morning. My numbers change substantially between arising and afternoon workout, when muscle and bone have both gone up. - breakfast and lunch nutrition. I haven't been looking at the scale before and after workout, but I'll try to remember to do that. Might be informative - or maybe not. Can't tell without looking.

My bone % never moves. Always identical.

Try it first thing in the morning, then after a workout. Mine goes up .2 - .3 and for no conceivable reason other than that my scale gets bone and muscle a bit confused.

These scales essentially just run an electric current through you and measure the resistance don't they? Maybe some passive electrical too.

I've wondered how much moist feet one day versus dry feet another day change readings. However even though I have a scale that does similar stuff, I tired of using those functions long ago and never got interested enough again to try out the moist vs dry feet thing. I just use the scale to weigh.

Maybe even one moist and one dry to throw another twist at it?

Understand I'm not discounting how accurate they may be, but like a lot of other things they are relying on generalizations from indirect measurements.

Yes. Each of these components has a known conductivity and I'm pretty sure the body is modeled as a set of parallel impedances. I'd be willing to bet that glycogen content doesn't affect the conductivity of muscle much.

Incidentally, you don't necessarily pee out the water bound in glycogen, nor the water formed in the metabolism of carbohydrate to water and CO2. It goes into the plasma just like any water you drink and if you're working out, it leaves the body as sweat and respiratory water as much as urine.

https://tanita.eu/body-composition-scales/

Water content changes muscle conductivity. My muscle percent between when I get up and later in the day goes up 1 or 2 percent. Similarly after exercise and my thighs are still pumped, it also goes up. However if I don't recover the lost glycogen, the next mourning my muscle percent number will have gone down 1 or 2 percent from the previous morning as well as my weight dropping 1 - 1.5 lbs.. I doubt that's from dehydration since I pee a few times in the night no matter what. OTOH if I do recover the glycogen, neither my morning weight nor muscle percent will have changed. It helps to have paid attention to one of these scales for many years. Whether that's glycogen being measured or simply the water content of the glycogen really doesn't matter. It does get measured.

How do you know how much glycogen you’ve synthesized?

How do you know how much glycogen you’ve synthesized and why would it vary?

Well, one can tell one's low on glycogen if one just can't move the bike normally - assuming there's no other good reason, like lack of recent exercise or really sore muscles on the bike. Glycogen synthesis normally varies with quantity of carbs ingested, though when on a carb-restricted diet, gluconeogenesis will occur to some extent. As that banana's guy says, "Carb the F up!"

OTOH, if you want to know how one can tell exactly how many calories/kg of glycogen, both muscle and liver, one has on board, I don't think one can without doing some very specific and rather odd workout(s). There was that old thing about glycogen depletion as part of a glycogen maxing effort before an event, but even then, one wouldn't really know, too much other stuff gets in the way. However, since some of us do have body comp scales, one could look at one's weight and body comp which one had before an exceptionally good ride and try to duplicate that. And in fact, that's what one does. I think that's what the OP was wishing to discuss.

I am not interested in trying to do this. I was referring specifically to your statement seeming to imply that you knew if you had “recovered the lost glycogen” or not.

I see. It's simply having a strong ride, for which the forecast is having normal numbers on the scale in the morning. Learned correlation. A long time ago, I tried to do a 40 mile moderate pace "recovery ride" after a particularly hard ride the day before. That's the only time I ever had a liver glycogen bonk. I thought I did well to make it home alive. So that's the limiter on the other end. I didn't have the scale then.

Okay, thanks

These types of scales are not really made for giving good quality snapshot numbers. The technology behind them is not that accurate. As has been mentioned above, they send a current through your body and measure resistance. Differences in resistance are due to water content in the body. Muscle has more water then fat. So a higher water percentage equates to more muscle mass. The calculations also use height (don't give yourself two extra inches like in your Tinder profile :)), and - I think - age. So the scales measure two things: weight & electrical resistance. All of the other numbers the scales give you are just the results math formulas.

Some of the detailed numbers and analysis mentioned in this thread above are difficult to get in a laboratory much less from a $100 bathroom scale.

Any one single measurement on any of these scales is pretty much worthless if you are expecting accurate numbers. And comparing numbers between just-rolled-out-of-bed and right after hard workouts on the same day may be interesting but is not what these scales are designed to do. I did some research about getting a scale last year and everything I read suggested taking your weight at the same time every day and the best time to do that is when you wake up, after emptying your system, and before eating or drinking anything. Due to the six to eight hours of sleep and fasting that will give a more consistent measurement from day-to-day. Waiting until later in the day will likely skew results based on what you've eaten & drunk and what exercise or other activities you've done each day.

Does that make these scales a waste of money? Not at all. Over time you'll see trends in the numbers to help see if your fitness and health plans are working. Maybe you are trying to lose, maintain or gain weight, or trying to get more lean, or adding muscle mass at a faster rate than fat mass. Over the course of several weeks the numbers from these scales should show the trend. Personally, I use my scale every morning I'm at home and log the numbers in a spreadsheet. I also keep a seven day rolling average of those numbers and pay most attention to the trend of those 7 day averages.

Having dropped 48 pounds since Jan 1, 2020 (based on seven day rolling averages of course) the numbers and trends from my scale have been additional confirmation that my exercise and diet plans are working. That's in addition to how my clothes fit, blood pressure, my performance biking, running, lifting weights, and just looking in the mirror. I don't care if the fat or muscle ##s the scale gives me are spot on accurate this morning. But I can see that they've changed in the right direction compared to two months ago. And by looking at the rolling averages I can see whether I've been consistent or jumping around over time (happy to say I'm usually consistent although there was a definite blip following my birthday weekend earlier this month :thumb:)

Following on what telebianchi wrote, if the scale just makes two measurements - conductivity and weight - then it cannot possibly determine accurately five outputs (your total weight, percentage bone, percentage fat, percentage muscle, percentage water). Mathematically, this is what would be called an underdetermined problem. To convert just 2 measurements, it must have some generalized algorithms that determine internal correlations between these supposedly independent variables. Those correlations are presumably taken from models based on laboratory measurements that are good generalizations, but may not apply to you.

HOWEVER, it is possible that the electrical conductivity measurement is not a single scalar, but something more sophisticated, i.e.,something like an oscilloscope, which would give conductivity in a frequency domain. If there were experimental data that showed that different materials (fat, water, etc.) had not only different conductivities, but also different phase response, then what I wrote in the paragraph above would not be accurate. I don't know if the scales are that sophisticated nor do I know that the materials have conductivities with distinct frequency dependence. Maybe one of you know.

MinnMan EE? My degree is electrical engineering and I agree with your assessment.

My gym has a fancy machine that we stand on and hold handles with our thumbs on a spot on the grips with our arms straight and away from our sides. This machine produces a lot of metrics including muscle density right and left side.

Per instructions, I wet my feet before running the test. The body fat and weight measurements seem about right and correlate to what I see in the mirror and how my clothes fit.

If the device applied five different frequencies, spectral analysis would be the ticket to differentiate composition; otherwise, rider needs to consistent when measuring WRT hydration, time of day, glycogen levels, etc

Not EE. Just a good background in physical science.

These scales measure impedance, and my guess is that they do so using a variety of frequencies. One has to stand there and wait a bit for the response.

They are obviously not accurate in the technical sense, but their comparative accuracy is useful once one has a few weeks of observations to interpret.