[Treadmill versus field trial. Movement analysis and pressure distribution in the athletic shoe]

Our current knowledge on interactions between runner and runningshoe is mainly based on treadmill measurements. In order to reveal stress load and adaptation on playing surfaces it was necessary to develop a combined measuring device out of 3-D video motion analysis and portable pressure measurement system. By means of a motor driven cart moving parallel to the subject with comparable position of cameras to the treadmill test it was possible to set up an identical trial for track and field. 12 subjects (male, age 24-32, size 9) were tested at a speed of 2.8 m/s. The varying conditions were treadmill and grass and two different constructed running shoes. 200 cycles and over 1000 steps were analyzed. The quantitative analysis of 37 parameters describing the contact phase was performed using the wilcoxon test for paired samples.-A qualitative comparison of running styles was introduced by using angle-angle-diagrams (knee and ankle by 3-D data) similar to those first described for 2-D by P.R. Cavanagh in 1973. It showed a huge interindividual variability under same conditions. Comparing the angle-angle-diagrams for the four different running conditions it was possible to classify them into three characteristic groups: non-adaptors, surface-adaptors and shoe-adaptors. Comparing track and field to treadmill measurements significant differences were found for the knee at impact: On treadmill the initial knee angle was 4.6 degrees more extended at a 13% higher angle velocity and a 30% higher angle deceleration (sig. p less than 0.05). A 7.3% higher impulse was found on grass at a 5.9% higher step length. No difference in maximum pressure was found. These results show that adaptation is performed mainly by the knee. Changing the motion pattern the knee seems to be capable of homogenizing the different stress loads to the foot. Comparing the running shoes significant differences were found in the motion of the ankle: a controversial behaviour was found to be on treadmill and grass. The pressure data revealed significant differences for the treadmill test to be in the heel area, for grass in the arch area. This points to an--up to now--unknown importance of the arch on unplain surfaces that are obviously influenced by the construction of the shoe and are not accessible by treadmill tests. The described different behaviour of shoes in treadmill and track and field tests points out the reduced validity of single treadmill tests.(ABSTRACT TRUNCATED AT 400 WORDS)