Fig. 6

Myofribrillar function, muscle fiber ultrastructure, and optimal muscle length following lengthening contractions in the TA muscle from mdx mice and effect of prior cardiotoxin injection. a Calcium maximally activated force of skinned muscle fibers (myofibrillar function) after nine lengthening contractions. b, c Representative images of electron microscopy from mdx mouse illustrating the absence of morphological alterations following nine lengthening contractions (c) as compared to before lengthening contractions (b). d Force drop following nine lengthening contractions in mdx mice, muscles were stretched to try to obtain a new optimal length (L0). e Force drop following lengthening contractions in the cardiotoxin-treated (freshly regenerated) mdx muscle. C57 mice were also shown. f Maximal force before lengthening contractions (initial) in mdx muscle treated with cardiotoxin. C57 mice were also shown. 0LC before lengthening contractions, 9LC after nine lengthening contractions, 9LC + newL0 muscles were stretched to try to obtain a new optimal length (L0) after nine lengthening contractions, Cardio muscle injected with cardiotoxin 3 weeks before, a significantly different from before lengthening contractions (p < 0.05), b significant difference between strains (p < 0.05), c significantly different from 9LC (p < 0.05), d significantly different from C57 (p < 0.05). n ≥ 20 per group for a; n = 7–10 per group for d–f