HARMONIC ASYMMETRY UNDER CHANGING TERRAIN GRADIENT IN CROSS-COUNTRY SKIING

Abstract

Aim. This study aims to conduct a comparative analysis of harmonic asymmetry indicators of cyclic movements in cross-country skiing under changes in terrain gradient. Materials and methods. The study involved 3 Masters of Sport and 5 Candidates for Master of Sport in cross-country skiing. Testing was performed on slopes with inclination angles of 0–1°, 6–7°, 8–9°, and 10–13°. The intervals were performed at three intensity levels (low, middle, and high) using the one-step skating technique. Angular velocity was assessed using a WitMotion sensor. Data were processed using Python 3.12. The angular velocity data from the sensor relative to the Z-axis were filtered to remove high-frequency noise using a low-pass filter. All measurements were segmented into individual swings (cycles). For each swing, the following para­meters were obtained: 1) oscillation amplitude, 2) oscillation period, and 3) the duration of positive angular velocity. Asymmetry was then calculated as the ratio of positive angular velocity duration to total swing time. Results. The trend of increasing asymmetry was more pronounced during high-intensity efforts on slopes compared to flat terrain. On 0–1° terrain, oscillation range (2X amplitude) averaged ~1000°/s, with asymmetry ~60%. As slope angles increased, the number of swings with asymmetry >50% increased, while the number with asymmetry < 50 % decreased. Conclusion. The study indicates that swing asym­metry shifts toward higher values with steeper terrain under identical intensity. Flat terrain exhibited a higher concentration of asymmetry values above 50% compared to slopes. These findings suggest a promising approach for measuring power output in cross-country skiing, analogous to potentiometer-based devices in cycling and rowing.