help me understand sarcopenia, I have read the wiki twice

The title is the whole question — help me understand sarcopenia, I have read the wiki twice — but here is why I am asking.

Some lean mass loss accompanies weight loss in any deficit. Resistance training and adequate protein intake are the two interventions with the best evidence for limiting the proportion.

On comparing yourself to composition figures from trials.

Published composition data comes from supervised populations with structured protocols, standardised scanning, and analysis populations that have been defined in advance. Your two scans at a local clinic, taken in different states of hydration, are not the same measurement.

Use your own baseline. The question worth asking is whether your own trajectory is going the way you want given what you are actually doing, and the honest answer usually requires measuring protein rather than estimating it and being truthful about training frequency. Neither of those is advice — a programme and a target are things to work out with somebody who knows your history.

How to make a DEXA comparison mean anything.

Same machine, same clinic, same protocol. Same hydration and fasting state, as far as you can manage. At least three to four months apart, because the measurement error is large relative to short-term change. Three scans rather than two, because the first pair cannot distinguish a trend from noise.

Do less than that and you have two numbers with an offset of unknown size, which people then react to by rebuilding a training programme. The free alternative — a few tracked lifts and a monthly waist measurement — is directionally informative, costs nothing, and is far harder to over-interpret.

Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.