During which stage of development are default patterns for movement established?

The correct answer is the embryonic stage, as it is during this period that the foundational framework for movement patterns begins to take shape. In the embryonic stage, critical neural development occurs, and early motor patterns start to develop in response to both genetic programming and environmental influences. The formation of motor patterns is heavily influenced by the nervous system's maturation, which primarily takes place in utero.

As the embryo develops, fundamental pathways for movement-related functions are set up, which will later facilitate more complex movement as development continues. The groundwork laid during this stage ultimately influences later stages of movement development, making it a crucial period for establishing these default patterns.

In contrast, infancy is centered around refining and practicing the movement patterns that were established earlier, adolescence involves further maturation and growth, and young adulthood emphasizes the exploration and optimization of these skills rather than their initial establishment.