Limiting factors in ski jumping take-off

The present study was designed to examine the factors which may hinder the execution of an effective take-off in ski jumping. Emphasis was placed on neuromuscular system of jumpers with special interest on balance of take-off under simulated laboratory and wind tunnel conditions. The test procedure for the Paromed Datalogger® used in the present study showed that this system could be used to measure pressure distribution under feet in ski jumping with only minor disturbance to jumper. The good fit between the measured relative pressure increase and the relative calculated centrifugal force during the inrun curve served as a rough indication of the validity of the system. Especially anteroposterior balance of jumper could be examined with the datalogger system. The results of this study showed that differences in plantar pressure and EMGs between the differently-sized jumping hills were smaller than expected. It seems that ski jumping training on small hills does not disturb the movement patterns for bigger hills and that it could also be helpful for special take-off training at low speed. The simulated and real ski jumping take-offs differed significantly in plantar pressure and muscle activation patterns. The centrifugal force due to the curvature of the inrun in real jumping hill conditions caused extra pressure under the fore and rear parts of the feet and therefore higher activation in all muscles. For the jumper, adequate sensory perception of this extra pressure and its release while entering the take-off table is obviously very important. The aerodynamic lift generated by the wind tunnel conditions brings simulated ski jumping take-off closer to field jumping conditions and helps the jumpers to perform take-off in the split second on the take-off table more effectively than has hitherto been believed possible. The reduced take-off time with higher rate of force production and minor changes in EMG emphasises the explosiveness of the ski jumping take-off