INTRODUCTION: A ski competition event has a ski jumping, Alpine skiing, and cross country skiing. All events are exercise modality of a lower limb by a Stretch - shortening cycle. Bosco et al. designed extra load jump test (called Bosco Jump) as conditioning evaluation in a ski event and physical ability test. This test evaluation is jumping height uses extra load on the shoulder with jumping by counter movement. Bosco jump is a test event applied by many sports events that used exercise for a Stretch - shortening cycle. The purpose of this study is investigated effect of a power products component by increase of extra load in Bosco jump by exercise for a stretching - shortening cycle. METHOD: These subjects were 13 male ski event athletes, 18-28 years of age. By this study, we used force platform (AMTI co.ltd) and derived an electrical signal of a floor reaction of a vertical direction and convert from analog to digital and stored it in a personal Computer. We calculated jumping height, peak power, a negative work and a positive work from data achieved by force platform. A jump movement carried different load (0, 10, 30, 50kg) with a barbell and we used reaction on force platform and randomly tried three times vertical jumping exercise, respectively. Duration of flight was used in calculating the change of bodily gravity. The highest amount of jump in three times trials were used to an analysis subject. During trials, put in enough rest to release of subject's fatigue. RESULTS: It was 48.4 ± 11.6cm at 0kg, and it was 41.5 ± 9.6cm at 10kg, and, in addition, it was 29.2 ± 7.1cm at 30kg, and jumping height for extra load was 21.4 ± 5.4cm at 50kg, Jumping height was declines with increase extra load. DISCUSSION: Figure 1. showed the mean and Standard deviation of peak power in extra load in the upper section. The statistical significant difference was not observed in power output by extra load (N. S.). In conclusion peak power may not be affected by extra load. However, as for force and the relations of velocity, it was thought that constitution rate of a force component and a velocity component induced into peak power output with increase of load because a significant correlation was found (p<0.001). CONCLUSION: Influence of a force component of power output increases with extra load, and effect of a velocity component decreases. Further it was admitted that contribution of a velocity component increased as it got closer to 0kg.
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