OBJECTIVE: To determine the comparative rate of resolution of a contusion resulting from mechanical trauma to skeletal muscle, as a function of one of four exercise regimens.

DESIGN: Randomized control trial. The four exercise regimens were: running with its onset immediately after injury, running with a 72 hr delay after injury, swimming with immediate onset, or swimming with a 72 hr delay. Control did not exercise.

SETTING: Small-animal laboratory.

PARTICIPANTS: Male Sprague-Dawley rats.

INTERVENTION: A small animal traumatizing machine applied to the biceps femoris.

MAIN OUTCOME MEASURES: The rate of contusion resolution was determined by a manual count of erythrocytes, leukocytes and collagen fibers in the contusion, and the data were analyzed using analysis of variance.

RESULTS: Exercise of any type produced a greater decline in erythrocyte count (28.2% after 32 days vs. control) than no exercise. Immediate onset of any of the exercise regimens after injury resulted in a greater decline in erythrocyte count (32.7% after 32 days vs. control) and in leukocyte count (17.3% after 32 days vs. control) than delayed onset. Running with either immediate or delayed onset of exercise after injury produced a greater decline in erythrocyte count (36.2% after 32 days vs. control) than swimming. Running with its onset immediately after injury produced the greatest overall rate of decrease in erythrocyte count (44.8% after 32 days vs. control), and the second greatest overall rate of decrease in leukocyte count (15.0% after 32 days vs. control).

CONCLUSIONS: Running with immediate onset is the regimen of choice. Any of the given exercises is preferable to no exercise, immediate onset of exercise is preferable to delayed onset, and running is preferable to swimming.

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