I gained 13.6 pounds of muscle in four months. Probably not.

I got my fifth DEXA scan yesterday. The number was on the iPad before I’d swung my legs off the table: lean mass 252.6 lbs, up from 239.0 in January. Plus 13.6 pounds of lean tissue in four months.

I lift five days a week and ate in a surplus the whole time, so some of that is real. But I’m 35 and a half, several years into serious training, and not on anything. Thirteen-plus pounds of muscle in a quarter is not how the body works at this stage. So before I believed the number, I went looking for where it came from.

Start with what the report actually measures. It says “Lean Mass,” and right below, in grey, it tells you what’s in that bucket: Muscle Mass, Organs, Blood and Stomach Contents. It never says how those split. The thing I care about — pounds of contractile skeletal muscle — isn’t a number the machine reports.

Glycogen is the big confound. Trained muscle stores roughly 15–18 g of glycogen per kg, and every gram drags about three grams of water with it. Topped off, at my size, that’s plausibly 4–6 lbs of glycogen and bound water sitting inside the muscle, and DEXA reads all of it as lean mass. The two scans weren’t matched, either: January I went in fasted, after a low-carb day; May I went in fed, mid-training-week, pre-workout carbs on board. If my muscle was more depleted in January than in May — it almost certainly was — then four or five pounds of the “gain” is plumbing, not tissue.

Then the noise. DEXA is good, not perfect. Reproducibility studies on the Lunar Prodigy put lean-mass variance at ±1–2 lbs on back-to-back scans, and it widens across months as positioning, hydration, and machine drift stack up.

So here’s the 13.6, itemized honestly:

• ~4–5 lbs — glycogen + bound water (optimistic)
• ~1–2 lbs — measurement noise
• ~1 lb — organ/blood/gut shifts at this size
• ~5–7 lbs — new muscle, best case

Five to seven pounds of real muscle in four months at 35 is still aggressive — that’s territory the literature reserves for younger, less-trained lifters. My honest guess is 2–4. And 2–4 lbs of actual muscle in four months is a good bulk. It’s just not the number on the report — the one I almost posted before I did the math.

The trend tells it cleaner than any single scan:

Two ~14-lb jumps, two boring scans in between. The boring ones — +5.2 over nine months, +3.2 over three — match both the literature and my actual lifting numbers. The jumps line up exactly with the scans I walked into hydrated, fed, and post-training-week. The real pattern isn’t “ten pounds of muscle a quarter, then plateau.” It’s “a couple pounds of muscle a quarter, and the rest is signal noise the DEXA faithfully logs as muscle.”

I start a twelve-week cut tomorrow, and the next scan settles it — fasted, low-carb day, matched to January. If lean drops 6–8 lbs while fat drops 15, that’s the glycogen-and-water tax coming due, and what’s left is what I built. If it drops 12+, the +13.6 was almost all smoke.

I don’t know which it’ll be yet.