Model of normal prepubertal growth.

Growth over the short term is a highly complex non-linear process. Contrasting models of short term growth have been proposed which include periodic growth cycles versus abrupt growth spurts with intervening growth arrest ('saltation and stasis'). The variability of short term growth has been characterised from a study of 46 healthy prepubertal children measured three times a week over one academic year using a combination of descriptive statistical approaches and regression modelling. Growth in childhood over one year is represented by a biphasic process comprising three to six unpredictable growth spurts, each of mean length 56 days (range 13-155 days), separated by periods of stasis (less than or equal to 0.05 cm height increment over more than seven days), each lasting a mean of 18 days (range 8-52 days) and accounting for at least 20% of the period of observation. This is superimposed on strong seasonal trends in growth with a declining growth rate over the autumn months reaching a nadir in midwinter, followed by a growth spurt in the spring. Human growth over short periods is therefore a discontinuous, irregular, and unpredictable process.