Effects of marathon running on running economy and kinematics

The present study was designed to investigate interactions between running economy and mechanics before, during, and after an individually run maratho n. Seven experienced triathletes performed a 5-min sub-maximal running test on a treadmill at an individual constant marathon speed. Heart rate was mo nitored and the expired respiratory gas was analyzed. Blood samples were dr awn to analyze serum creatine kinase activity (S-CK), skeletal troponin I ( sTnI), and blood lactate (B-La). A video analysis was performed (200 frames . s(-1)) to investigate running mechanics. A kinematic arm was used to det ermine the external work of each subject. The results of the present study demonstrate that after the marathon, a standardized 5-min submaximal runnin g test resulted in an increase in oxygen consumption, ventilation, and hear t rate (P < 0.05), with a simultaneous decrease in the oxygen difference (% ) between inspired and expired air, and respiratory exchange ratio (P < 0.0 5). B-La did not change during the marathon, while sTnI and S-CK values inc reased (P < 0.05), peaking 2 h and 2 days after the marathon, respectively. With regard to the running kinematics, a minor increase in stride frequenc y and a similar decrease in stride length were observed (P < 0.01). These r esults demonstrate clearly that weakened running economy cannot be explaine d by changes in running mechanics. Therefore, it is suggested that the incr eased physiological loading is due to several mechanisms: increased utiliza tion of fat as an energy substrate, increased demands of body temperature r egulation, and possible muscle damage.