CATCH-UP in LINEAR GROWTH
Group of children
at age 2
Length deficit at age 1
Catch-up in linear growth requires that children grow faster (at a higher velocity) than expected for their age and sex.
Play age 2
A cycling analogy illustrates this: for the blue cyclists who have fallen behind (children with growth retardation) to catch up to the green cyclist (the growth standard), the blue cyclists must pedal faster than the green cyclists. By covering a greater distance (gaining more height in centimeters) between age 1 and age 2, the blue cyclists narrow the gap with the green cyclist (the growth deficit shrinks).
Reset to age 1
Since the blue cyclists (the treated children) may still be cycling slower than the green cyclist (the growth standard), the gap between them may still have grown over time. Consequently, a positive impact on linear growth of an intervention does not imply that catch-up growth has occurred. Even if the treatment group improved relative to the comparison group, the height deficit of the treatment group relative to the standard may have widened.
For a nutrition intervention to have an impact on linear growth, children with growth retardation receiving the treatment must gain more height in centimeters than children who do not receive treatment (the comparison). In terms of the cycling analogy, the blue cyclists must cycle faster than the red cyclists, thus creating a gap between both groups between age 1 and age 2.
Length deficit at age 2
Impact at age 2