Dexamethasone and recovery of contractile tension after a muscle injury.

Muscle strains, frequently the result of a lengthening contraction, sometimes are treated with corticosteroids. We tested whether an injection of dexamethasone administered soon after muscle injury would minimize inflammation and facilitate the recovery of contractile tension. We applied one eccentric contraction on the tibialis anterior of 76 rats, which were randomly assigned to one of three groups: sham-injured plus dexamethasone, injured plus vehicle, and injured plus dexamethasone. Electrophysiology, histology, and reverse transcription-polymerase chain reaction were used to study the relation between contractile tension, inflammation, and the expression of inflammatory molecules. The single eccentric contraction led to a reversible muscle injury characterized initially by reduced contractile tension and inflammation. The dexamethasone injection reduced the expression of interleukin-1beta and transforming growth factor-beta1 compared with injured vehicle-injected controls and led to a transient improvement of contractile tension 3 days after the injury. No adverse effects were seen for as much as 3 weeks after the dexamethasone injection. The data indicate that one dose of dexamethasone administered soon after muscle strain may facilitate recovery of contractile tension without causing major adverse consequences in this experimental model.

The contribution of contractile pre-activation to loss of function after a single lengthening contraction.

PURPOSE: Some muscle injuries are the result of a single lengthening contraction. Our goal was to evaluate the contributions of angular velocity, arc of motion, and timing of contractile activation relative to the onset of joint motion in an animal model of muscle injury using a single lengthening contraction. METHODS: The intact tibialis anterior (TA) muscle of rats was activated while lengthened, preceded by a maximal isometric contraction of 0, 25, 50, 100, or 200 ms. The lengthening contraction was performed at two different angular velocities (300 or 900 degrees/s) and through two different arcs of motion (90 degrees or 45 degrees). RESULTS: Muscle contractile function, as measured by maximal isometric tetanic tension, was significantly decreased only when the TA was activated at least 50 ms prior to the motion, regardless of angular velocity or arc of motion. CONCLUSION: The data indicated that the duration of an isometric contraction prior to a single lengthening contraction determined the extent of muscle injury irrespective of two different angular velocities.