acquired measures for many children can follow a size percentile rather closely
when graphically plotted, the actual biology of growing does not occur at the rate
inferred from the graphic curve. Indeed, rather than slowly accruing at less than a
millimeter each day, total body length in infancy can increase by more than 1 cm in
a day, followed by an interval lasting days to weeks during which no further
increase occurs (Lampl et al. 1992 ). The documentation of the stepwise pattern by
which growing occurs requires attention to methodological details for valid and
accurate high-frequency measurement acquisition and unbiased data analysis
(Lampl 2012 ). Saltatory growth is the pattern of normal growth documented across
developmental ages in endochondral and intramembranous bone among species
fromfish to rats, rabbits, lambs, and children (Goldsmith et al. 2003 ; Hermanussen
1998 ; Hermanussen et al. 1992 ; Noonan et al. 2004 ; Thalange et al. 1996 ; Caino
et al. 2006 ). Traditional approaches of infrequent data collection and analytic
approaches based on curvilinear modeling simply did not direct attention to this
avenue of investigation in earlier decades. The details of how children grow were
revealed only after time-intensive anthropometric data collection protocols were
initiated (Lampl and Johnson 1997 ) with careful attention to errors of measurement
(Lampl et al. 2001 ), in concert with analytic methods that did not default to con-
tinuous functions or impute data in lieu of actual measurement (Lampl 2012 ).
With these new approaches, the prospective documentation of growing indi-
viduals on a daily timescale has revealed an array of phenotypic and molecular
biomarkers. Growth in length/height occurs by quantum jumps of up to 20 mm and
head circumference expansion by similar saltations on the order of 1–5mmina
24-h interval, after pauses of 1 day to a number of weeks depending on the age of
the individual (Lampl et al. 1992 ; Caino et al. 2006 , 2010 ; Lampl and Johnson
2011b). Studies aiming to identify biomarkers of these growth events include the
work of Tillmann et al. ( 2000 ), quantifying urinary growth hormone (uGH) , uri-
nary insulin-like growth factor-1 (uIGF-1) , free pyridinoline (fPYR) , and free
deoxypyridinoline (fDPYR) as biomarkers of growth. Our own work has focused
on biomarker recovery from urine and feces, which is advancing the understanding
of time-specific correlates of saltatory growth events in terms of steroid hormones
(Thompson et al. 2010 , 2011 ; Thompson and Lampl 2013 ). Clarifying the mech-
anisms of normal saltatory growth is a basic science challenge. This is needed not
only for better understanding of normal and abnormal growth in general, but will
provide a fundamental explanatory model for the everyday experience of parents
and their children.
The Subjective Experience of Growing
“My legs really, really hurt.”An estimated 10–30% of children between the ages of
three and twelve awaken in the night with musculoskeletal pains localized primarily
to their shins, knees, and ankles. Generations of grandparents have comforted
children’s moans with the comment that these are“just growing pains”and they
54 M. Lampl et al.