RSSThe Western Roman economy was highly urbanized, relying heavily on trade, specialization, and technological diffusion for its prosperity. This was all enabled by a high capacity state until the late 2nd c. CE or so. The collapse was gradual… then all at once.
The 5th c. CE wrought a rapid depopulation of the urban areas and an associated improvement in stature because of the subsequent reduction in disease. Per capita income likely fell with reduced trade and specialization (the archeological evidence strongly suggests a decline in the quantity and quality of consumer goods, disappearance of currency from common life, literacy all but disappeared, smaller buildings of lower-quality materials, etc.), but statures *rose* quickly and rapidly as indicated by human remains (less urbanization meant less disease). See Fig. 4: https://delong.typepad.com/rome.pdf
It is unlikely that the increase in stature was due to the health and vigor of the couple hundred thousand 5th c. CE Germanic arrivals (“New Romans” — ha!), as the incumbent Roman populations were likely in the several millions.
In much in the same vein (but reversed), as the UK and USA industrialized in the early 19th c., statures *declined* as those economies developed into higher per capita income urbanized ones. Statures don’t rise with improving per capita incomes until the late 19th c. because of urbanization effects.