People with neuromuscular diseases have very limited muscle force. Many of them rely on mobile arm supports to move their arms. Most of these supports incorporate gravity balancers, i.e., spring-loaded mechanisms that achieve a constant total potential energy, thus eliminating any preferred position. The springs and the mechanism topology and dimensions are designed to exactly or approximately balance the weight of the user’s arm. Quasistatically, the mechanism, once statically balanced, can thus be moved virtually without operating energy. In case of change of effective arm weight, e.g., due to picking up an object or putting on a coat, the support mechanism should ideally be readjusted. In all available support mechanisms, this adjustment is associated with considerable mechanical effort, while clearly this application would benefit greatly from an energy-free adjustment. This paper will present an arm support that includes a novel design concept to adjust spring-based static balancers with no need for external energy. This concept will be explained, and several variants will be shown. Subsequently, the application of this concept in a mobile arm support will be described in detail, including preliminary clinical trial results.