A public safety expert called by the defense says George Zimmerman's physical capabilities were inferior to those of 17-year-old Trayvon Martin.

Former police officer Dennis Root was called as a witness Wednesday by defense attorneys.

Root testified that Martin was in better physical shape than Zimmerman, and that the neighborhood watch volunteer wasn't any athlete.

Zimmerman is pleading not guilty to second-degree murder, claiming he fatally shot Martin in self-defense during a struggle.

[Associated Press]