Bioimpedance and hydration: why the number moves posts 61–71

Lean mass in these measurements includes water, so a change in hydration appears as a change in lean mass.

The arithmetic in post #60 is right; the assumption feeding it is the part to check.

Neither method is capable of detecting the month-to-month changes that people report detecting month to month.

Adding a source would improve this post and I do not have one to hand.

Two people in this thread mean different things by bioimpedance and hydration and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.

Post #64 describes the usual case. This is about the unusual one.

Photographs under fixed lighting and posture are a genuine record and are the hardest of these to standardise.

Somebody will have a better source than mine, and I hope they post it.

Adding the measurement that post #64 says would settle it.

Where a facility reports a precision figure for its own machine, that number is more useful than any published average.

It is a small point and it changes the answer, which is an awkward combination.

Bioimpedance is considerably less precise and is strongly affected by hydration state, which is why readings move overnight without anything having changed.

Percentage body fat is a ratio, so it changes when either component changes. A rising percentage during weight loss is arithmetic before it is physiology.

On post #67 — agreed on the reasoning, with one qualification.

The version of bioimpedance and hydration that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.

Nobody has said the unglamorous part of bioimpedance and hydration yet, so: most of the variation is explained by things that are boring to write about and easy to check.

Standardise the conditions: same time of day, same hydration, same recent training, same machine. Most of the variability is protocol rather than physiology.