Table 1.

Infant Growth Metric Descriptions and Interpretations

Growth Metric	Technical Description	Interpretation	Symbol	Units	Equation
Infant Slope	Slope of the tangent line at the 1st inflection point (a growth rate constant)	Proxy of overall infant growth rate	β1	[kg/months]	6
Infant Peak Growth Velocity	Peak instantaneous velocity on the 1st logistic curve	Peak instantaneous growth rate in infancy	PGV	[kg/months]	8, first terma
Age at Infant PGV	Age at the 1st inflection point and when instantaneous growth rate peaks	Infant growth tempo; how early or late the peak infant growth rate occurs	δ1	[months]	6
Infant Weight Plateau	Asymptote of the 1st logistic curve; an intermediate weight, and starting point for the 2nd logistic curve	Intermediate plateau in weight at the end of the infant growth spurt	α1	[kg]	6
Infant Growth Spurt Duration	Time required to growth from 10% to 90% saturation on the 1st logistic curve (a function of β1)	Time it takes to complete 80% of infant growth; Age when 90% of the infant growth is attained	Δt1	[months]	10a
Curve 2 Saturation	The %saturation of the 2nd logistic curve when the first logistic curve is at 50% saturation (age = δ1)	Measure of how well-defined the infant growth spurt is from the 2nd spurt; we define ≤10% as sequential spurts, >10% as overlapping	S2	[%]	9

^aAssumes sequential growth spurts (S₂≤10%) where the 2^nd logistic term has negligible contribution