Performance Analysis in Ski Jumping with a Differential Global Navigation Satellite System and Video-Based Pose Estimation

Abstract

This study investigated the explanatory power of a sensor fusion of two complementary methods to explain performance and its underlying mechanisms in ski jumping. A differential Global Navigation Satellite System (dGNSS) and a markerless video-based pose estimation system (PosEst) were used to measure the kinematics and kinetics from the start of the in-run to the landing. The study had two aims; firstly, the agreement between the two methods was assessed using 16 jumps by athletes of national level from 5 m before the take-off to 20 m after, where the methods had spatial overlap. The comparison revealed a good agreement from 5 m after the take-off, within the uncertainty of the dGNSS (±0.05m). The second part of the study served as a proof of concept of the sensor fusion application, by showcasing the type of performance analysis the systems allows. Two ski jumps by the same ski jumper, with comparable external conditions, were chosen for the case study. The dGNSS was used to analyse the in-run and flight phase, while the PosEst system was used to analyse the take-off and the early flight phase. The proof-of-concept study showed that the methods are suitable to track the kinematic and kinetic characteristics that determine performance in ski jumping and their usability in both research and practice.

Experimental Validation of Real-Time Ski Jumping Tracking System Based on Wearable Sensors

“…In comparison with a recent study, which uses dGNSS and achieves a better accuracy of smaller than [ 15 ], the advantage of the investigated system is that it is unobtrusive in contrast to the backpack and antennas at the helmet needed for the dGNSS.…”

“…These studies incorporate the use of inertial measurement units (IMUs) [ 13 , 14 ], force insoles or differential Global Navigation Satellite System (dGNSS) [ 15 ]. The latter has the disadvantage of being obtrusive since antennas on the helmet and a backpack have to be attached to the ski jumpers.…”

Kinematic Determination of the Aerial Phase in Ski Jumping

“…In each data collection, the same dGNSS method was applied, in which the head trajectories of the athletes were captured using a dGNSS with a receiver (Alpha-G3T, Javad, CA, USA) in a backpack and an antenna (G5Ant-2AT1, Antcom, Torrance, CA, USA) mounted on the helmet, as shown in Figure 2. The antenna mounting point can be considered a reasonable representation of the athlete as a point mass as soon as the ski jumper has reached a steady posture, but not during the take-off and landing phases [35].…”

“…Measurements with dGNSS are extensively used and validated in alpine skiing for position, velocity, and acceleration-related parameters [29][30][31][32][33], but have rarely been used in ski jumping [34]. However, a recent study has shown the possibilities dGNSS provides to efficiently collect data from the start of the inrun to the landing [35]. The use of this method allows measurement of the trajectory with ±0.05 m global position accuracy [36].…”

“…The use of this method allows measurement of the trajectory with ±0.05 m global position accuracy [36]. As long as carrier phase kinematic double difference ambiguities can be fixed, the position accuracy of geodetic receivers and high antenna quality is such that velocity and acceleration, derived from position-time information, can be used to describe the aerodynamic forces during the glide [35].…”