Effects of marathon fatigue on running kinematics and economy

The influence of marathon fatigue on both running kinematics and economy was investigated with 8 subjects. The measurements included a treadmill test at 3 steady submaximal speeds performed before and after the marathon. One complete left leg cycle was videotaped at 100 Hz from the left side at each speed. The analysis included contact time (braking and push-off') and flight time as well as displacements and angular velocities of the left hip and knee. This analysis was complemented by the measurements of the electromyographic (EMG) activity of the gastrocnemius muscle at each running velocity, and energy expenditure (E) of the last 30.s at the 2 slowest speeds. The results revealed significant increases of E at these 2 speeds, but the changes were not related to kinematic changes, which were greatly individual. However, the relative duration of the push-off phase was significantly increased at the 2 slowest speeds, and the gastrocnemius muscle presented higher integrated EMG values in the respective braking (NS) and push-off phases at the 2 fastest speeds. This might indicate a loss of tolerance to impact during the belt contact. The results failed, however, to demonstrate that running kinematics and running economy are interrelated when fatigue progresses. It is also possible that observed kinematic changes might reflect some adaptation to fatigue more than real failure to compensate for it.