Ski Position during the Flight and Landing Preparation Phases in Ski Jumping Detected with Inertial Sensors

Abstract

Ski movement plays an important role during landing preparation, as well as in the whole ski jumping performance. Good landing preparation timing and correct ski position increase the jump length and reduce the impact forces. Inertial motion units (IMUs) placed on the skis could constitute a promising technology for analyzing the ski movements during training. During regular summer trainings, 10 elite athletes (17 ± 1 years) performed jumps while wearing IMUs and wireless force insoles. This set-up enabled the analysis of a possible correlation between ski movements and ground reaction force (GRF) during landing impact. The results showed that the pitch during the landing preparation is the most influential movement on the impact kinetic variables since it is related to the angle of attack, which affects the aerodynamics. The ski position at 0.16 s before landing did not influence the kinetics because the athlete was too close to the ground. During the impact, the roll angle did not correlate with GRF. Moreover, each athlete showed a different movement pattern during the flight phase. Concluding, the combination of IMUs and force insoles is a promising set-up to analyze ski jumping performance thanks to the fast placement, low weight, and high reliability.

Landing in Ski Jumping: A Review About its Biomechanics and the Connected Injuries

“…Therefore, it was not possible to recommend if one of the two landings guarantees lower GRF. In addition, the distribution of the force on the front and the rear foot during telemark seemed to be case specific [3,4] and, in general, asymmetry between the two feet was found for 81% of the parallel landing and 50% of telemark, differently from what suggested by the FIS ICR regulations. In general, the telemark landing has been positively and negatively criticized [23], being biomechanically safer than the parallel leg landing.…”

“…), while (2. ) shows the end of the landing [3] landing coincides with the minimum of the kinetic signal following the second normal GRF peak after the impact, corresponding with the end of the eccentric phase 1 .…”

“…In addition, the longer the time of the braking action and the longer the elastic properties of the skis are acting on the ski jumper, helping to decrease the GRF [23]. As a result, the lower the landing speed with which the athlete impacts the ground, the lower is the load on his/her musculo-skeletal system [3,4,17]. The athlete should find a good compromise when exploiting the aerodynamics to have longer jumps and to break down the speed that ranges between 80 km/h and 85 km/h while approaching the landing on a normal hill [50].…”

“…Regarding the duration of the two phases, studies show how the landing preparation starts round about 0.4-0.5 s before the landing impact, when the main movements of the ankles and hips happen [17], followed by the ski pitch around 0.16-0.36 s before the impact [3]. Finally, the athlete starts moving the knees around 0.16 s before the impact [17].…”

“…7 Simulation of the ground reaction force acting during the impact when landing at different length by an average athlete and on the normal hill of Oberstdorf, Germany (see foonote 1). The red line stays for the Pareto frontier for the jump length vs. touchdown impact force athlete [4,9] or, as an alternative, on the skis [2,3,18]. Thanks to the fast post-processing of the data and to a complementary dedicated software interface, a visual and objective feedback can be provided to the jumpers soon after the end of the training [5] (Fig.…”