Magnitude of Injury to the Extensor Digitorum Longus Muscles Following Single Lengthening Contractions at Different Temperatures In Vitro and In Situ
Dedhia, Manish M.
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Extensor digitorum longus (EDL) muscles from 17 male CD-1 mice were studied at 25º C. Data collected in vitro at 25º c were compared with data previously collected at 35º c by others. I tested the hypotheses that 1) the amount of injury produced by single-lengthening contractions performed in situ does not differ compared with contractions performed in vitro, 2) following single-lengthening contractions, the EDL muscles are injured to a lesser degree at 25 °c than at 35º C. The EDL muscles were injured in vitro by activating the muscle to contract to 85% of maximum force and then lengthened with isovelocity ramps. The muscles were passively shortened 5% of fiber length (Lf) and then lengthened to 50% and 75% of Lf at velocities of 0.5, 1.0, 2.0, and 3.0 Lf/second. The magnitude of injury was assessed immediately afterward by the deficit-in-force compared to the contralateral controls. The amount of power absorbed was calculated by a computer. For the in vitro protocol, injury to the EDL muscles was observed during both the 50% and 75% length changes at each velocity. At 25º c, the magnitude of injury to the EDL muscles after single-lengthening contractions of 50% of Lf at 0.5 Lf/second, were similar for the in situ and in vitro protocols. At different temperatures, greater injury to EDL muscles was observed at 35 °C than at 25 °C. Although mechanical factors are likely involved to the immediate injury to the fibers, the greater injury at a higher temperature suggests chemical factors may also be involved.