Introduction and Purpose: Unique activation strategy of eccentric contraction predisposes the muscle to damage. Type II muscle fibers are more susceptible than type I to muscle damage, so it seems that Velocity interferes in mechanical stress and thus muscle damage. The purpose of this study was to compare slow versus fast contraction velocity of acute eccentric exercise induced knee extensor muscle damage on running economy and metabolic responses in trained females.
Materials and Methods: Sixteen trained young females randomly assigned into two groups: high velocity contraction eccentric exercise (240°.s-1) and low velocity (60°.s-1). In order to induce muscle damage subjects in high and low velocity groups performed 20 and 5 sets of 15 eccentric contractions respectively, with a load equal to 150٪ of the maximal voluntary isometric torque (MVC) of knee extensors with dominant limb. Muscle damage indicators (MVC) was recorded before, 1 and 48 h after eccentric exercise and running economy (submaximal Steady-state vo2) and metabolic responses were recorded at 60, 70, and 80% of pre-determined  vVO2max, 24 h before and 48 h after eccentric exercise.
 
Results: Muscle damage indicators changed significantly in both groups (p<0.05) in a way suggestive of muscle damage. There was no significant difference for muscle damage indicators, running economy and metabolic responses at three different intensities of running between groups.
Conclusion: Four-fold difference in contraction velocity of eccentric exercise induced muscle damage was not sufficient to induce a difference in muscle damage, running economy and metabolic responses when the tension duration was equalized.