Indirect flight muscles of Mhc^DA1/Mhc^DA1, Mhc¹⁰/Mhc¹⁰ organisms fail to assemble properly and worsen with age: In late-stage pupae, myofibrils are distorted with some disruptions of thick and thin filament packing, M- lines are poorly formed and Z-lines are diffuse. In 2h-old adults, more severe filament irregularities are present, with gaps between thick and thin filaments, aberrant filament alignment. In 2d old adults, adjacent myofibrils tend to merge.

Indirect flight muscles of 2h and 2d old Mhc^DA1/+, Mhc¹⁰/+ show essentially normal myofibrils with occasional filaments missing from myofibrils that display similar to control M- and Z-lines. These muscles show decreased power output, slower kinetics and enhanced stiffness compared to controls.