Magnitude of Injury to the Extensor Digitorum Longus Muscles Following Single Lengthening Contractions at Different Temperatures In Vitro and In Situ
Dedhia, Manish M.
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.
v, 25 p.
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