measurement
Somatotype
William Sheldon's body-type classification (ectomorph, mesomorph, endomorph) — loosely correlated with training responses.
Somatotype is a mid-20th-century body-classification system that persists in fitness culture. Modern evidence shows body type is a tendency, not a fixed metabolic cage — individuals of any type can gain muscle or lose fat with the right inputs. Differences in BMR between types are small (<5%). Useful as loose heuristic, weak as a plan.