PHYS-42 · Principle

Same plan as my friend, much smaller gain. Am I a non-responder?

One block cannot say. In trials of untrained adults most of the spread between people after one block was test noise, the less fit gained more, and flat results mostly moved with more training.

How the body works, agreed across the reviews below; a study entry shows what one experiment measured.

well supported, with open questions namedApplies to everyoneWell supported — gains are larger in the less fit and grow with dose, and in controlled trials most of one block's spread is measurement error; contested — whether true trainability differences exist: no strong evidence…

Practical Application

Same plan as my friend, much smaller gain. Am I a non-responder? One block cannot say. In trials of untrained adults most of the spread between people after one block was test noise, the less fit gained more, and flat results mostly moved with more training.
What it means for training: forecast from the group range (SYNTH-93); after a flat block that was done, change one lever and judge it over 2-3 blocks (practice, SYNTH-42).
What it does not mean: labels such as "non-responder" or an athlete type (SYNTH-13), or that everyone gains the same.

Mechanism

A change is true response plus error and daily variation; only a spread wider than a control group's shows true differences (REF-430).
In 24 controlled trials most of the spread in VO2max change was measurement error (REF-1274); in 42 adults who repeated a block, individual change barely reproduced (REF-498); HERITAGE had no control arm, so its spread includes noise (REF-429).
Gains are larger at lower starting fitness (REF-465); in adults not described as trained, flat results vanished with more sessions (REF-996, uncontrolled).
Sex: alike on identical intervals (REF-1243); untrained men gained more on matched endurance training (REF-1281); one relative forecast for both (SYNTH-93).

Common misreading

"HERITAGE shows half of us cannot respond."

Backs

SYNTH-04 "expect responders and non-responders" (a spread, not a class) · SYNTH-42 "One block is one noisy point" · SYNTH-93 "Never call an athlete a non-responder from one block"

Sources

Renwick et al. 2024 REF-1274 · Paper ↗
Atkinson & Batterham 2015 REF-430 · Paper ↗
Bouchard et al. 1999 REF-429 · Paper ↗