Modeling stability and change in strength development: a study in adolescent boys.

The purpose of this study was to investigate stability and change in different expressions of strength development in adolescent boys using structural equation modeling. Three models were used: Markov simplex to study stability or tracking, Wiener or random walk to investigate fanning-out or spread effects in change, and latent growth to study differences in individual pathways of change as well as group changes. In the Leuven Growth Study, 588 male subjects were followed for 6 years with a mean age of 12.7 years at the onset of the study. Vertical jump, arm pull, and bent arm hang were used to mark the following strength factors: explosive strength, static strength, and functional strength. All models were tested with robust estimation procedures based on the software EQS 6.0. Main results and conclusions are as follows: 1) all strength factors showed moderate to high tracking, with low values of instability in relative position of the subjects in their developmental channels; 2) the fanning-out effect is not obvious, although some evidence showed a spread effect in functional and explosive strength; 3) there are marked interindividual differences in developmental pathways of strength manifestations; 4) strength development is linear and also has some curvilinearity, something akin to a breaking effect; 5) linear trend is negatively correlated with initial status and the leveling-off effect is also negatively correlated with the linear change. Copyright 2003 Wiley-Liss, Inc.