Myosin isolated from IFMs of wild-type transgenic control (PwMhc2) and R146N lines was assessed for ATPase parameters (N = 5): (A) Ca-ATPase activity, (B) basal Mg-ATPase activity (C) actin-activated Mg-ATPase activity (Vmax), (D) actin affinity relative to ATPase (Km) and (E) catalytic efficiency (Vmax/Km). Actin sliding velocity (F) was determined using the in vitro motility assay, with at least 30 filaments tracked per myosin preparation (N = 3). For all parameters, mean ± S.D. values are given. These were assessed for statistically significant differences by Student’s t-tests. *p<0.05, **p<0.01, ***p<0.001, ns, not significant.