INTRODUCTION: Competitive alpine skiing is a sport that occurs between 40 and 150 km/h. At that speed, there are many details that could go unnoticed by coaches, especially when the differences between skiers are fractions of a second. Small differences in turn cycle structure translates into better performance on the turn. However, the influence on performance along a ski run (linked curves) has not been investigated yet. The aim of this study was to assess the influence of turn cycle structure on the performance of elite alpine skiers using an inertial measurement unit (IMU) in different slalom (SL) course settings. METHODS: An IMU device was attached to the lower back of skiers. Four 10-gate SL courses were set: a flat-turned (FT), a steep-turned (ST), a flat-straighter (FS) and a steep-straighter (SS). Five elite alpine skiers (21.2 ± 3.3 years, 180.2 ± 5.6 cm, 72.8 ± 6.6) completed several runs at maximum speed for each SL course. A total of 77 runs were obtained. The skiers` performance was evaluated with the total time of each run calculated through a validated Magnet-Based Timing System (M-BTS). For each run, the acceleration signal on the Y-axis (lateral axis) was used to identified two main phases within the ski turn: Initiation (INI) and steering (STE) phases. By fusing the accelerometer information with the M-BTS, that provides the position of the gates on the magnetometer signal, it was possible to divide the STE phase by the turn`s gate position leading to the steering phases into (STEIN) and out (STEOUT ) of the turn. For each run, the times corresponding to the same phase were added together, so the total time was decomposed into three partial times: INI time, time of STEIN and time of STEOUT. The two steering times were added together to obtain STEIN+OUT time. Statistical analyses were performed to assess the influence of turn cycle structure (partial times) on the total descent time. Pearson`s linear correlation coefficient was used to calculate correlation. A Linear Mixed Model (LMM) was implemented for each partial time, where the skier corresponded to the random factor, the total time variable was the response variable and the partial time variable was the xplanatory variable. RESULTS: Fast total times correlate with a longer INI time in FT, a shorter STEOUT time in the FT and FS and a shorter STEIN+OUT time in the FT and SS courses. The LMM used for the analysis revealed that in the FT-course for each second increase in the INI time, the total time is reduced by 0.45 s, and for every one-second increase in the STEOUT and STEIN+OUT times, the total time increases by 0.48 s and 0.31 s, respectively. CONCLUSION: Regardless of the SL set up, similar characteristics were observed in turn cycle structure for the fastest runs. To enhance descent performance, the skier should lengthen the INI time and shorten the STEOUT and STEIN+OUT time. Future studies could use an IMU to detect turn phases and analyze them using the other built-in sensors.
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