Fatigue-induced changes in decline running

Objective. Study the relation between muscle fatigue during eccentric muscle contractions and kinematics of the legs in downhill running. Design. Decline running on a treadmill was used to acquire data on shock accelerations, muscle activity and kinematics, for comparison with level running. Background. In downhill running, local muscle fatigue is the cause of morphological muscle damage which leads to reduced attenuation of shock accelerations. Methods. Fourteen subjects ran on a treadmill above level-running anaerobic threshold speed for 30 min, in level and −4° decline running. The following were monitored: metabolic fatigue by means of respiratory parameters; muscle fatigue of the quadriceps by means of elevation in myoelectric activity; and kinematic parameters including knee and ankle angles and hip vertical excursion by means of computerized videography. Data on shock transmission reported in previous studies were also used. Results. Quadriceps fatigue develops in parallel to an increasing vertical excursion of the hip in the stance phase of running, enabled by larger dorsi flexion of the ankle rather than by increased flexion of the knee. Conclusions. The decrease in shock attenuation can be attributed to quadriceps muscle fatigue in parallel to increased vertical excursion of the hips.