Elastic distortion of the actomyosin complex is fundamental to force generation by muscle. In isometric contraction, actin and myosin filaments cannot respond to the rotation of the light-chain (LC) binding domain during the myosin power stroke. Instead, the myosin head, and actin and myosin filaments become elastically distorted, thus generating muscle force. Despite this fundamental relevance of elastic distortion, it remained unclear which structural element of the myosin head domain becomes elastically distorted. It was hypothesized that the LC binding domain itself becomes elastically distorted. We addressed this question by studying functional effects of three naturally occurring familial hypertrophic cardiomyopathy (FHC)- related missense mutations in the myosin head domain (Arg723Gly, Arg719Trp and Ile736Thr) in human soleus muscle fibers. The mutations are located in the converter domain of the myosin head which forms a link between LC domain and catalytic domain. Two mutations located near the long -helix of the LC domain increased active force and resistance to elastic distortion (fiber stiffness) in contraction, relaxation, and rigor, while cross-bridge cycling kinetics were unchanged. A mutation near the converter surface did not affect any of these parameters. Increased resistance to elastic distortion by mutations in the converter domain implies that the converter is the part of the myosin head where most elastic distortion occurs while other parts act more like rigid bodies. Our data show the potential of using FHC-related mutations in the myosin head domain to assign functional features like elastic distortion to particular subdomains of the myosin head.