Regional Hypertrophy

The answer depends entirely on the metric, and the right one flips the result.

§ 2.1 — Absolute lbs is the wrong metric; proportional growth is the right one

Hypertrophy is better measured proportionally. Arms are much smaller than the trunk, so they can't add as many absolute pounds, and grading by pounds quietly penalizes them. As a share of each region's own baseline:

• Arms grew the most, +14.1%, on the most volume (46.5k lb).
• Trunk grew +7.8% at middling volume.
• Legs grew the least, +5.4%, on the least volume.

Ranked by proportional growth, the order matches the training-volume order exactly (Spearman +1.0). Ranked by absolute pounds, the trunk looks like the winner and the correlation flips to −0.5, purely because the trunk is bigger. The takeaway is to pick the metric that matches the question.

Variables on this page

• Lean Δ % — proportional lean change, 100 × lean_delta / lean_t0 (the hypertrophy metric).
• ± band % — the 95% precision band expressed as a share of baseline (larger for small regions like arms).
• Volume / Sets — Σ (weight × reps) and working-set count in the window.
• Lean Δ (lbs) — the absolute change, kept only to show why it misleads.

What this does and doesn't show

With the right (proportional) metric, the most-trained region also grew the most, a clean training signal the absolute view hid. It doesn't prove causation. There are only three regions and about 11 logged days, and the hydration/glycogen confound still applies. Glycogen also loads preferentially into trained muscles, which pushes proportional growth in the same direction, so part of arms' +14% is probably trained-muscle water rather than fiber. Read it as directional.