Final answer:
The body maintains balance through multiple systems, with the diagonal line being the most active visually. The midsagittal plane divides the body into equal right and left halves, which is crucial for balance but not represented by a diagonal line.
Step-by-step explanation:
The body maintains balance in all planes through a complex interplay between different systems, predominantly the vestibular system in the inner ear, the eyes, and the muscular system. However, when discussing the planes themselves, a diagonal line typically exhibits the most dynamic qualities according to visual perception principles, as it suggests motion or potential for change in balance. Contrastingly, a midsagittal plane divides the body into equal right and left parts, whereas a coronal plane would separate the ventral and dorsal (front and back) sections of the body, and a transverse plane creates a cross section by cutting perpendicular to the body's long axis.