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Mikko Virmavirta and Paavo V. Komi

This study measured the takeoff forces exerted by jumpers during the 70-m ski jumping competition of the 1988 Winter Olympics in Calgary. Instrumentation consisted of four force plates installed under the snow of the takeoff platform. The results indicated that the greatest force was already exerted 149±9 ms before the release. The second force peak appeared closer to the edge of the takeoff platform. The correlations between the variables measured in this study were generally weak but some were considered important. The official approach velocity of the first round and relative maximum force as well as the mean relative force during the whole takeoff sequence of the second round correlated to length of jump. The mean relative forces at the end of takeoff and for the whole takeoff sequence were significantly higher among the best jumpers. It is concluded that although the force analyses among the jumpers do not reveal conclusive interrelationships, the fast development of the takeoff forces may be an important prerequisite for successful ski jump performance.

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Mikko Virmavirta and Paavo V. Komi

Electromyographic (EMG) activities of gluteus maximus (GL), vastus later-alis (VL), vastus medialis (VM), tibialis anterior (TA), and gastrocnemius (GA) were measured telemetrically from four world-class athletes during the entire ski jumping performance. Integrated electromyographic activities (IEMG) were calculated from the different phases of jump. TA and GA showed alternate activation during the curve, suggesting that maintenance of the inrun position is a process requiring continuous active control. VL and VM were observed to contribute mostly to the entire takeoff phase whereas GL became strongly active within the last 4 meters of the takeoff. GA was slightly but continuously active during the inrun and showed only a small increase during takeoff. The quick lifting of the skis, as evidenced by the activation of TA, does not seem to allow effective use of GA at the end of the takeoff. Strong continuous activity of the knee extensors and TA dominated the midflight phase whereas the activation of GL and GA increased toward the end of the flight.

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Mikko Virmavirta and Paavo V. Komi

The Paromed Datalogger® with two insole pressure transducers (16 sensors each, 200 Hz) was applied to study the feasibility of the system for measurement of plantar pressure distribution in ski jumping. The specific aim was to test the sensitivity of the Paromed system to the changes in plantar pressure distribution in ski jumping. Three international level ski jumpers served as subjects during the testing of the system. The Datalogger was fixed to the jumpers’ lower back under the jumping suit. A separate pulse was transmitted to the Datalogger and tape recorder in order to synchronize the logger information with photocell signals indicating the location of the jumper on the inrun. Test procedure showed that this system could be used in ski jumping with only minor disturbance to the jumper. The measured relative pressure increase during the inrun curve matched well the calculated relative centrifugal force (mv2 · r‒1), which thus serves a rough estimation of the system validity. Strong increase in pressure under the big toes compared to the heels (225% and 91%, respectively) with large interindividual differences characterized the take-off. These differences may reflect an unstable anteroposterior balance of a jumper while he tries to create a proper forward rotation for a good flight position.

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Mikko Virmavirta, Juha Kivekäs, and Paavo Komi

The effect of skis on the force–time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

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Anton Arndt, Gert-Peter Brüggemann, Mikko Virmavirta, and Paavo Komi

This study was concerned with identifying important flight characteristics of the ski jump at the end of the early flight phase and describing how these characteristics developed from the run-in through the takeoff and during the early flight phase. The K90 individual competition of the 1994 Olympic Winter Games was analyzed. The 2-D data (takeoff) were collected by a high-speed video camera, and the 3-D analysis (early flight) used an algorithm whereby two cameras followed the jumpers through the early flight phase. Center of mass (CM) velocities at takeoff and after early flight and CM heights at these positions had no significant linear correlations with total distance. Only small differences in these parameters were distinguished between better and poorer performers. Significant differences between jumpers were identified in angular parameters at takeoff and in early flight. A combination of five defined flight angles yielded an R 2 value of .84. It was found that the complex movement sequences involved in ski jumping were therefore more important in their contributions to optimal flight position than the ballistic properties of the ski jumper reduced to a single point model.