Trypan blue positive myofibers increased with time following a single bout of repeated muscle stretches.
Med Sci Sports Exerc 2004 May; 36(5)(Suppl 1):S289
PURPOSE: To examine the early time course of muscle injury following a single bout of 50 repeated stretches by using different markers for cell damage. METHODS: Sprague Dawley rats (n = 6) were injected with Evans blue or Trypan blue 24 hrs before the stretch-injury protocol. The injury protocol consisted of a single bout of 50 stretches to activated plantar flexor muscles with an inter-stretch rest time of 40 seconds using a manual stretching protocol. The distal part of the medical gastrocnemius muscles were removed at 0, 1, 6, and 48 hrs post-injury, sectioned and stained. Injured myofibers were visualized using the autofluorescence of the dyes and were counted. Some samples were stained for albumin, W3/13 or double-labeled for laminin and desmin using immunohistochemical techniques. Computer-montages of the entire muscle sections with laminin staining were used for counting the total number of myofibers. RESULTS: Approximately 1 percent of the myofibers contained dye immediately after the stretching protocol. At 1 hr post-injury, the number of dye-positive fibers had doubled but not all were positive for albumin. Immdediately following the stretching protocol (0 hr), some of the injured myofibers were devoid of desmin but positive for laminin; these muscle samples did not contain any W3/134 cells. However, at 1 hr post-injury, a few W3/13 positive cells were visible and at 6 hrs were numerous. CONCLUSIONS: Following a single bout of repeated stretches, evidence of myofiber injury was present which increased with time even after the stretching protocol had ended but before the arrival of large numbers of W3/13 positive cells. The mechanisms producing myofiber injury appear to continue during the recovery period but before any marked inflammatory response has occurred.
Muscles; Physiology; Physiological-function; Physical-reactions; Injuries; Muscle-tissue; Tissue-culture
Medicine and Science in Sports and Exercise
West Virginia University, Morgantown, West Virginia