The dorsal longitudinal muscles (DLMs) of homozygous flies are not parallel, but appear contorted. A mesh of F-acting aggregates is seen in the DLMs and no sarcomere organisation is seen.

Ultrastructural analysis shows that indirect flight muscles of homozygous flies lack a filament lattice and lack sarcomere structure; thick, but not thin filaments are visible, and irregular electron-dense structures (Z-bodies) similar in appearance to Z-discs are seen as bands scattered among the thick filaments.

Ultrastructural analysis shows that indirect flight muscles of heterozygous flies have poor myofibrillar structure and filament bundles appear to cross from one array to the next.

The indirect flight muscles of homozygous animals have wiggly fibres before 78 hours after puparium formation (APF). After 78 hours APF, wiggly and detached fibres are seen. At eclosion, a partial hypercontraction phenotype (bunched fibres) is seen and flies more than 2 days old show a hypercontraction phenotype of the fibres.

Heterozygotes rarely exhibit free myofibril fibres and if present they are cut, fragmented, torn and gapped. Indirect flight muscle fibres are wavy in homozygotes and normal in heterozygotes.