Four kinds of complex alloyed steel have been tested under uniaxial strain conditions within strain rate range of 215÷550 m/s. The kinematics of straining was studied by using SEM and optical microscopy of post-shocked specimens. The cross-section of targets is found to contain the mesoscopic rotational structures of complex configuration. Besides the free surface velocity, interference technique used allows the mean particle velocity profile and velocity variance to be registered in every shock loading. The spall strength is theoretically and experimentally found to be maximum at the strain rate where velocity variance equals to velocity defect. This condition means that local strain rate at the mesoscale equal to macroscopic strain rate. T hat strain rate corresponds to maximum density of rotations at the mesoscale.