The purpose of this study was to identify the characteristics of the ground reaction force (GRF) production within the elite ski jumpers. We measured the GRF exerted perpendicular to the take-off platform during take-off motion in the actual ski jumping situation. Twelve ski jumpers of the Japanese national ski team took part in this study. We calculated the following variables; the maximum force (F_max1) during 10-6.2 m before the take-off edge and the maximum force (F_max2) during 6.2-0 m before the edge. Then we calculated a quotient of F_max2 to F_max1 (F 2/F 1). We calculated the maximum value of vertical velocity of the center of gravity (V_max). We also calculated the minimal value of vertical displacement of the center of gravity (DCG_min) and its time duration from the edge (T 1).

F_max1, F_max2 and F 2/F 1 had no significant correlation with Vmax. These results would suggest that the elite jumpers could attain almost the same velocity by their own take-off style. F 2/F 1 was positively correlated with T 1 and negatively correlated with DCG_min respectively. These results suggest that the force produced on the latter part of the take-off platform such as F_max2 had some influence on the counter movement and the timing of beginning of the take-off movement.

This study showed new system for evaluating swimming power. This system was able to evaluate swimming force and power by only measuring swimming velocity. The purpose of this study was to show the usefulness of this new system for swimming training, and to verify the system for estimating swimming power.

The body of equipment for estimating swimming power (EESP) was made from wood, and was shaped like a kickboard. The body of EESP floated and the resistant part was attached to the underside of the board in the water. The resistant part was altered for the measurement of different levels of load. The subjects were eight female competitive swimmers, who swam 25 m front crawl as fast as they could under two conditions. One condition was free swimming, the other condition was semi-tethered swimming with EESP.

When the EESP was towed with an electorical towing machine that evaluated velocity and force simultaniously, the relationship between towing velocity and force on each load was a significant second order relation (r > 0.99, p < 0.001).

The relationship between swimming force and velocity was a significant linear relation (r = -0.97±0.02), when subjects swam with towing EESP. The swimming velocity on a 25 m sprint tended to increase significantly with the increase of swimming power (r = 0.87, p < 0.01). The results indicate that this system is able to estimate swimming power by only evaluating swimming velocity during use of EESP.