Effect of fatigue on leg kinematics and impact acceleration in long distance running

Abstract

The effect of fatigue on impact acceleration on the shank, stride rate, knee angle and hip vertical excursion was studied in 14 subjects in 30 minutes treadmill running above their anaerobic threshold (AT) speeds. Respiratory data were collected to determine the AT speed and to indicate the progressively developing fatigue. The following changes ( P<0.05) were obtained from the 1st to the 30th minute of running: average stride rate decreased from 1.46±0.05 to 1.39±0.03 seconds −1 ; average angle at maximal knee extension position increased from 13.8±3.1° to 17.2±4.2°; average knee flexion resulting from foot strike decreased from 13.6±6.3° to 8.1±3.0°; average hip vertical excursion between highest position to peak acceleration position increased from 5.1±1.5 to 6.2±1.2 cm. The average impact acceleration on the shank, measured by means of an accelerometer attached to the tibial tuberosity, increased from 6.9±2.9 to 11.1±4.2 g. It was concluded that the obtained kinematic changes due to fatigue were consistent with the substantially higher impact accelerations, increasing the risk of overload injuries in the shank.