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How accurate is the body composition at the gym?



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I had a body composition at the nutritionist a few months ago. It seemed accurate based on the findings. I have since lost some weight from 134.4 to 125.5 lbs. but I do NOT feel like I have bulked up muscle, just thinner overall. I am still doing the same basic exercises machines, I haven't even really went up on the resistance or reps. I only make it to the gym maybe once a week. I don't do free weights or heavy weight lifting etc.

Today I used a body composition scale at the local gym and it has my body fat at 15.5%. 3 months ago and 9 pounds heavier I had a body fat of 25% at the nutritionist office. It is 2 different machines so that's why I am questioning the accuracy. My BMI is now 22.4 so within the normal range but not low however according to the scale at the gym my body fat of 15.5% seems really low.

Any thoughts? I don't have plans to go back to the nutritionist so I can't compare the results.

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3 hours ago, 2Bsmaller18 said:

I had a body composition at the nutritionist a few months ago. It seemed accurate based on the findings. I have since lost some weight from 134.4 to 125.5 lbs. but I do NOT feel like I have bulked up muscle, just thinner overall. I am still doing the same basic exercises machines, I haven't even really went up on the resistance or reps. I only make it to the gym maybe once a week. I don't do free weights or heavy weight lifting etc.

Today I used a body composition scale at the local gym and it has my body fat at 15.5%. 3 months ago and 9 pounds heavier I had a body fat of 25% at the nutritionist office. It is 2 different machines so that's why I am questioning the accuracy. My BMI is now 22.4 so within the normal range but not low however according to the scale at the gym my body fat of 15.5% seems really low.

Any thoughts? I don't have plans to go back to the nutritionist so I can't compare the results.

You can ask a trainer or dietician about a healthy body fat range.

Only my opinion, Body composition scales are not 100% accurate. You can buy them online for home use. They are a guideline to work on goals. Are you using body fat %, muscle mass, bone density and Water weight to achieve new goals?

  • Maintain your weight
  • Lose weight
  • Lowering body fat
  • Raising body fat
  • building muscle

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I've read that they're not that accurate. They give you a ballpark figure, though. Methods such as Water weighing, skinfold calipers, and DEXAscans tend to be more accurate.

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The body fat scales measure impedance (electrical resistance) between your feet (or in the better ones, between your hands, too.) As such, they are sensitive to your body's Water content - hydration - so variations in your hydration will change the readings. On mine, there was a 4-5 point difference between first thing in the morning, when we tend to be dehydrated, and late afternoon, when we tend to be more fully hydrated. So, being consistent with time of day is important. There can also be a point of two difference day to day from simple hydration variations due to diet, activity, weather, hormones, etc. Of course, there can always be differences between scales (or any other measuring instruments.)

The most accurate way to measure body composition is via autopsy, but that has the undesirable side effect of having to be dead first. Next best is generally considered to be DEXAscan, which is pretty good, though there can still be differences between machines and even software loads (as it is dependent upon large population datasets.) Hydrostatic, or water dunking, (or the related BodPod, which uses air instead of water) is next best, but may be a bit quirky for us former fatties as the excess skin that we often have can create some errors in the results. The calipers are generally considered to be the least worst, as they are very dependent upon operator skill and experience to interpret the results, and given the problems of skin condition (excess) that we typically have, they are virtually worthless for us.

I have found that the scales work fairly well if you have one at home and use it consistently, same time each day. Given the day to day hydration variations that we can have, it is only good within a point of two. I found that using a moving average of daily measurements worked well - as I was losing, I may have seen BF readings in the 32's and 33's, after some time I would start seeing 31's and the 33's dropped away, so I was consistently in the 31-32 range, and so on. It couldn't reliably show may anything closer, but that's a pretty good ballpark. How much variation would one see if you did a DEXA or dunking every day (I suspect similar, but maybe a bit narrower bandwidth on the variation.) Using this method, the scale was pretty consistent with the water dunkings that I had done.

The way the scales are used in gyms and doctors' offices - read at month or more intervals - they are of limited value (even detrimental) as the variations from time of day and day to day hydration levels overwhelm whatever true changes have actually happened since the last reading. I played with the one in our surgeon's office when my wife was going through her surgery, and over the couple of weeks that we were in town for it, I had "gained" about 10 lb of muscle mass with no weight change. Right - from walking around the hospital and SF some every day!

For the OP, if you can, try to use their scale each time you go to the gym, preferably before working out and dehydrating yourself, and keep track that way. Your readings may or may not be "accurate" on an absolute basis, but relative to where you are now and in the future, it should give some useful insight into your progress,

Note, that mid teens BF% is quite lean for a woman (though about average, or "normal" for a man,) while mid 20's is "normal" for a woman. Mid teens was my target when I was in losing mode.

Good luck in further progress!

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