Many properties of languages, including sign languages, are not uniformly distributed among items in the lexicon. Some of this nonuniformity can be accounted for by appeal to articulatory ease, with easier articulations being overrepresented in the lexicon in comparison to more difficult articulations. The literature on ease of articulation deals only with the active effort internal to the articulation itself. We note the existence of a previously unstudied aspect of articulatory ease, which we call reactive effort: the effort of resisting incidental movement that has been induced by an articulation elsewhere in the body. For example, reactive effort is needed to resist incidental twisting and rocking of the torso induced by path movement of the manual articulators in sign languages. We argue that, as part of a general linguistic drive to reduce articulatory effort, reactive effort should have a significant effect on the relative frequency in the lexicon of certain types of path movements. We support this argument with evidence from Italian Sign Language, Sri Lankan Sign Language, and Al-Sayyid Bedouin Sign Language, evidence that cannot be explained solely by appeal to constraints on bimanual coordination. As the first exploration of the linguistic role of reactive effort, this work contributes not only to the developing field of sign language phonetics, but also to our understanding of phonetics in general, adding to a growing body of functionalist literature showing that some linguistic patterns emerge from more fundamental factors of the physical world.