DMD tissues exhibit contractile weakness. (A) Schematic representation of tissues before film release, at baseline stress, and at peak stress. (B) Representative images of healthy (i and ii) and DMD (iii and iv) tissues at baseline (i and iii) and peak stress (ii and iv). Blue rectangles represent film length. The red bar represents the tracking of the film edge. The yellow arrows represent the distance between the projected film length and the unstressed film length. The yellow bars represent the change in projected film length from baseline stress (top bar) to peak stress (bottom bar). (C) Representative stress trace of a healthy and DMD contraction in response to 23-Hz stimulation. n = 1 film for each condition. (D) Baseline stress is plotted for the healthy and DMD conditions on D3 and D6. (E) Peak stress is plotted for the healthy condition on D3 and D6 and the DMD condition on D6. For the DMD condition, no contraction was observed on D3. (F) Dynamic stress is plotted for the healthy condition on D3 and D6 and the DMD condition on D6. For the DMD condition, no contraction was observed on D3. Data points represent the mean ± SEM. For all stress measurements (D–F): for the healthy D3 condition, n = 11 films, 3 chips; for the healthy D6 condition, n = 10 films, 3 chips; for the DMD D3 condition, n = 12 films, 2 chips; for the DMD D6 condition, n = 14 films, 3 chips. **, P < 0.05 relative to both conditions on either day. *, P < 0.05 relative to the DMD condition on D6. Error bars represent median ± SEM.