[Biomechanical considerations of impact forces and foot stability in running]

The interaction between "man-shoe and surface" is presented as a model to discuss the complexity of human locomotion. Only if the physiological system "man" interacts positively with the physical requirements of shoe and surface quality running will become effective and economical. Especially during the early ground contact phase the hardness of the shoe construction determines the height of the vertical impact load. These adaptations have consequences in the emg amplitudes during the stretch activation phase of the contact. Comparing various jogging shoes with altered construction properties it can be shown that the "hardness" of the shoe material is well adapted by the variation in the emg amplitude. The influence of the amount of pronation on the impact forces has been confirmed in a separate study. Increased pronation resulted in an increased emg amplitude in the extensor muscles whereas activation in the flexor muscles was decreased. By means of different shoe and insole constructions it is possible to adjust the "man-shoe-surface" interaction to an optimum to carry loads by muscles, joints and ligaments and to avoid overuse and injuries.