Final answer:
The lower leg muscles involved in walking are controlled by the lumbar and sacral levels of the spinal cord, where the central pattern generators for walking are located.
Step-by-step explanation:
The rhythmic flexion and extension of lower leg muscles involved in walking are primarily controlled by the lumbar and sacral levels of the spinal cord. These areas contain the networks of neurons known as central pattern generators (CPGs) that are responsible for the generation of rhythmic muscle contractions for walking. The lumbar plexus arises from the lumbar spinal nerves and enervates the pelvic region and the anterior leg, while the sacral plexus comes from the lower lumbar and sacral nerves, giving rise to the sciatic nerve, which extends through the hip joint and gluteal region into the upper posterior leg.