State v. Lara
In State v. Lara, 183 Ariz. 233, 234-35, 902 P.2d 1337, 1338-39 (1995), the Arizona Supreme Court explained that the requirement that an act be "voluntary" is simply a codification of the common law requirement of actus reus, a requirement grounded in the principle that a person cannot be prosecuted for his thoughts alone, and that the voluntary act requirement does not modify the mens rea required for the offense.
The court therefore concluded that expert testimony that the defendant suffered from a brain disorder that caused him to fly into a rage "as if by reflex" was insufficient to support a voluntary act instruction. Id.
The court stated that the statutory requirement that the conduct include "a bodily movement performed consciously and as a result of effort and determination" simply means that the defendant engage in "a determined conscious bodily movement, in contrast to a knee-jerk reflex driven by the autonomic nervous system." See id.