Some types of expertise benefit from anatomical changes from practice during critical developmental periods:
For example, ballet dancers’ ability to turn out their feet, and baseball pitchers’ ability to stretch back with their throwing arm are linked to practice overload at around 8- to 11-years-of-age, when the children’s bones are in the process of being calcified (Ericsson & Lehmann, 1996).
More generally, early and extended training has been shown to change the cortical mapping of the brain area controlling fingers of string players (Elbert et al., 1995) and the flexibility of fingers (Ericsson & Lehmann, 1996). Also interesting is the recent finding that intense music practice influences the development of myelin around nerves in critical brain regions. The development of white matter (myelin) occurs in different brain regions at different ages (Bengtsson et al., 2005). Even the famous ability to name musical notes in isolation — ‘the gift for perfect pitch’ (Simonton, 2005, p. 312) — is linked to a very early developmental window of opportunity. It is most easily acquired between ages 3 and 5 years during early music instruction, when children encode stimuli in absolute terms (Levitin & Rogers, 2005). At older ages music students encode musical tones in relation to other tones and thus acquire relative pitch, finding it far more difficult to acquire absolute pitch.
Importantly, these differences in adult abilities are explained with critical periods, rather than with genetic differences between individuals. There are interesting examples of late starters, who attempt to attain the physical adaptations of the early starters but are not able to do so and where the training of the late-starting adults may lead to injuries (Pieper, 1998).