The purposes of this study were to determine 1) how running kinematics varied across two different speeds (200 and 268m/min), 2) to what degree intense interval training sessions affected running mechanics and 3) whether these changes correlated to changes in running economy (RE). Eleven highly trained male endurance athletes (average VC^max = 72.5 ± 4.3 ml/kg/min) performed three intense interval running workouts of 10 x 400m at an average runnin g velocity of 357.9 ± 9.0 m/min, with a minimum of 4 days between runs. Recovery duration between trials was randomly assigned at 60s, 120s, and 180s. The following biomechanical variables were used to assess running kinematics during the last 3 minutes prior to and following each workout at speeds of 200 and 268m/min: maximum knee flexion in support (KFLEX), minimum knee velocity during stance (KVEL), maximum plantar flexion angle at toe-off (PFLEX), shank angle at heel strike (SANG), mean trunk angle during stride cycle (TANG), mean vertical oscillation of center of mass (VOSC), and stride cycle length (SL). Results of this study affirmed our hypothesis that speed significantly impacts on some kinematic variables (KVEL,SANG, SL), and to a degree has shown that pre and post test and recovery conditions creating a fatigued state altered 2 of the kinematic variables (KVEL and VOSC). However, none of the other kinematic variables measured were altered by speed or fatigue in any substantial way, nor were there any clear correlations between changes in running economy and mechanics. Whether the significant kinematic changes that occurred reflect adaptations to fatigue, rather than a failure to compensate for it, is not clear. The interrelationship between metabolic and biomechanical markers of training and performance appears to be complex and somewhat individualistic.