Female flies expressing Mhc^E701K in a homozygous Mhc¹⁰ background completely lack flight ability. Two day old flies are unable to beat their wings, and a "wings-up" phenotype is present. The jump ability of two day old females is also severely reduced compared with controls.

Myosin isolated from the indirect flight muscles of flies expressing Mhc^E701K in a homozygous Mhc¹⁰ background has significantly reduced catalytic activity compared to control myosin. CaATPase, MgATPase, and actin-stimulated MgATPase activity (V[[max]]) and catalytic efficiency (the ratio of V[[max]] / actin affinity relative to ATPase (K[[m]]) ) are all reduced. K[[m]] is increased. The actin sliding velocity stimulated by mutant myosin is significantly reduced compared to that of control myosin.

Myosin isolated from the indirect flight muscles of flies expressing Mhc^E701K in a Mhc¹⁰ mutant background has an increased propensity to aggregate compared to control myosin. The mutant myosin molecules have collapsed heads that frequently pack into aggregated clumps reminiscent of wild-type motors exposed to elevated temperatures. Only 22.5% of myosin exhibit the normal two headed structure.

The indirect flight muscles of female flies expressing Mhc^E701K in a Mhc¹⁰ mutant background exhibit ultrastructural defects that become progressively worse with age. During the late pupal stages M-lines and Z-discs are distinguishable, but the myofibrils show disruption of integrity and lack the round shape seen in controls. In two hour old flies the myofibrils show loss of visible M-lines, with decreases in myofibril integrity and hexagonal packing. By two days old the myofibrils show severe ultrastructural deterioration, with broken and streaming Z-discs and a loss of thick filaments and M-lines. The fibers show sarcolemmal membrane invaginations and protrusions and contain rimmed vacuoles fused with additional membranes. Cyclical spiral membranes are seen that are reminiscent of the sarcolemmal inclusions found in human skeletal myopathy.