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Predicting the maturity offset and age at Peak Height Velocity (PHV)
This is an excerpt from Growth, Maturation, Physical Activity, and Sport-3rd Edition by Robert M. Malina.
The original sex-specific equations for the prediction of maturity offset, defined as the time before PHV, include CA, height, weight, sitting height, and estimated leg length among the predictors (Mirwald et al., 2002). Modified offset prediction equations include CA and height in girls and either CA and sitting height or CA and height in boys (Moore et al., 2015). Maturity offset is subtracted from CA at the time of prediction to provide an estimate of predicted age at PHV. A more recent equation for boys based on CA, height, weight, and estimated leg length predicts a maturity ratio; CA divided by the maturity ratio provides an estimate of age at PHV (Fransen et al., 2018).
The majority of studies that have applied the prediction equations to date have used the Mirwald et al. (2002) equations. A question of relevance is the accuracy of the predictions compared to observed ages at PHV based on longitudinal records of height. The validity of the Mirwald et al. maturity offset prediction equations was evaluated in three longitudinal series for which age at PHV of individual boys and girls was known (Malina and Kozieł, 2014a, 2014b; Kozieł and Malina, 2018; Malina et al., 2016, 2021b);. The samples used in the development of the prediction equations were followed between 1964 and 1999, whereas those in the three validation studies were followed between 1960 and 1990. All samples were of European ancestry (White). Mean ages at PHV and the range of ages at PHV in the samples used to develop the maturity offset prediction equations and in the three validation studies overlapped those in longitudinal studies of European and North American youth between the 1960s through 1990s, and all are included in the summary of ages at PHV in table 7.8 (see also Malina et al., 2021b).
Results of the three studies in samples of girls 8 through 16 years of age and of boys 8 through 17 or 18 years of age were consistent in showing major limitations of the prediction equations. As expected, predicted maturity offset increased with CA at prediction. The trend with CA was likely related to the predictors in each equation (i.e., sitting height and estimated leg length, height, and weight), each of which increases with CA. Correlations between CA and predicted maturity offset with the Mirwald et al. (2002) equations were, for example, 0.97 in girls and 0.95 in boys in the longitudinal Fels sample (Malina et al., 2016). Predicted ages at PHV, estimated as CA minus predicted maturity offset, also increased, on average, with CA at prediction, and the increase occurred through the CA range beyond observed ages at PHV in the longitudinal validation samples.
Because age at PHV was known in the longitudinal studies, CA at prediction minus observed age at PHV provided an estimate of actual maturity offset at each observation. Variation in predicted maturity offset within each CA group was consistently reduced compared to variation in observed ages at maturity offset (Kozieł and Malina, 2018; Malina et al., 2021b). Variation in predicted ages at PHV was also reduced compared to variation in observed ages at PHV in each sample. Variation in predictions among youth classified as early, average, and late maturing on the basis of observed ages at PHV is considered in chapter 8.
Application of the modified maturity offset prediction equations (Moore et al., 2015) in two of the longitudinal series provided similar results (Kozieł and Malina, 2018; Malina et al., 2021b). However, variation in predicted maturity offset and in turn predicted age at PHV was reduced with the modified equations compared to the original prediction equations.
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