When young guys who already work out do a lot of high-volume weight training for 6 weeks, their muscles grow mostly because of fluid and non-contracting parts inside the muscle cells, not because they’re building more of the actual muscle-building proteins — and this change sticks around for over a week after they stop training.

Even if you do a lot of heavy weight training for 6 weeks, your muscle fibers don’t actually get more of the main building proteins—so the idea that your muscles grow by diluting those proteins with extra fluid probably isn’t right.

When young guys who haven't lifted weights before do strength training for 10 weeks, their muscle fibers grow in a way that makes them stronger, not just bigger with extra fluid. It's like building real muscle instead of just puffing it up.

Even though muscles get bigger after 10 weeks of weightlifting, the individual muscle fibers don’t necessarily get thicker — the growth might come from how the fibers are arranged, not from each one swelling up.

How long you lift weights—up to 6 months—doesn’t seem to change the number of muscle fibers you have, according to this claim.

After about 10 weight workouts, your muscles don’t just look puffy from water anymore—they actually start getting bigger because the muscle fibers themselves are growing.