The purpose of this investigation was to examine the influence of running velocity, stride characteristics, training background, gender, and caliber of a runner on the changes in ground contact time during a 400-m run. Thirteen male and 4 female sprinters ran a 400-m time trial on the track, and 8 male sprinters and 6 male endurance athletes ran a simulated 400-m trial at constant velocity on the treadmill. A special shoe insert was placed in the track spike to determine contact time, and a video camera was used to determine split times for each 40 m. Two threshold points were identified during the 400-m run, with the first occurring when the running velocity began to decrease. The threshold points were affected by the individual running strategy and reflected fatigue-induced changes in the running velocity; they also were independent of gender, training background, and caliber of an athlete.
Ari Nummela, James Stray-Gundersen, and Heikki Rusko
Antti P. Leppävuori, Matti Karras, Heikki Rusko, and Jukka T. Viitasaio
A new method was developed for measuring the distribution of real time ground reaction forces under the snow ski. A platform composed of 20 separate beams was buried in snow under the ski track. Vertical, cross horizontal, and longitudinal horizontal force components were measured with strain gauge bridges separately on each beam, and the results were recorded with a data logger at 90 Hz. The test results for two types of skating skis are described. Anomalous behavior was observed in horizontal force components, where negative force values were recorded on some sections of the ski at the end of the initial kick phase. This suggests that some parts of the ski edge pushed in the opposite direction from the kicking force. This is interpreted to be due to a sharp bending along the bottom edge of the ski. It is concluded that the method could be used to measure 3-D dynamic forces under snow.