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MERRICK, M. A., J. M. RANKIN, F. A. ANDRES, and C. L. HINMAN. A preliminary examination of cryotherapy and secondary injury in skeletal muscle. Med. Sci. Sports Exerc., Vol. 31, No. 11, pp. 1516–1521, 1999.The purpose of this study was to document the presence of secondary injury in skeletal muscle, to quantify it, and to determine whether it is altered by acute cryotherapy.Crush injuries to the triceps surae of 19 adult male Sprague-Dawley rats were either treated continuously with ice for 5 h (N = 10) or received no ice treatment (N = 9). After treatment, tissues were assayed for the reduction of triphenyltetrazolium chloride (TTC) to triphenylformazan (formazan red). TTC reduction is indicative of oxidative function and serves as an indicator of cellular damage.A significantly lower TTC reduction rate was seen in both cold-treated injured tissue (6.59 ± 1.01 μg·mg−1·h−1) and nontreated injured tissue (4.48 ± 0.79 μg·mg−1·h−1) compared with uninjured controls (ice group = 7.94 ± 1.49 μg·mg−1·h−1, no-ice group = 6.62 ± 0.75 μg·mg−1·h−1). These data indicate that crushing of muscle tissue produces injury measurable with the TTC reduction assay. Additionally, in crush-injured tissues, a significantly lower TTC reduction rate was seen in untreated tissues (4.48 ± 0.79 μg·mg−1·h−1) compared with ice treated tissues (6.59 ± 1.01 μg·mg−1·h−1), indicating that cryotherapy reduces the magnitude of secondary injury.From these data, it can be concluded that secondary injury occurs after primary crush injury and that secondary injury is retarded by acute treatment with 5 h of continuous cryotherapy.