Statically-balanced technology is often used to compensate partial or full gravity force exerting on a mechanism in order to reduce the effort of driving the mechanism. Since such compensation is static, when a statically-balanced mechanism is used for dynamic applications, it will still have impedance (mechanical resistance to input motion) because the mechanism still subjects to the inertia forces although the gravity force has been compensated. Such a dynamic effect is undesirable for many applications, especially for those required to physically interact with humans and hence, the impedance property needs to be fully understood and possibly minimized in the design and/or operation of a statically-balanced mechanism. This paper studies the impedance property of passive statically-balanced mechanisms. Based on the study result, optimization strategies are proposed in order to optimize the operation of a statically-balanced mechanism. The strategies are then applied to a spring-based reduced-gravity simulation mechanism to figure out an optimal set of configurations in the workspace where the mechanism has the lowest impedance and the highest zero-gravity simulation fidelity.