Abstract
This study used wireless technology to investigate joint kinematic characteristics of the four alpine skiing disciplines. Knee and hip angles were measured in 20 national team alpine skiers during 253 ski runs under FIS regulation, including: 85 Slalom (SL), 123 Giant Slalom (GS), 29 Super Giant Slalom (SG), and 16 Downhill (DH). Data were analyzed by outside (OL, n = 2,087) and inside leg (IL, n = 2,015). The proportion of concentric and eccentric phases (extension and flexion respectively for the knee extensors) as well as the proportion of the quasi-isometric phase defined between ±20°.s−1 depended on the discipline in interaction with the IL/OL (p < 0.001). The results showed a lower knee quasi-isometric duration on OL in SL (11%) than other disciplines (DH: 38%; SG: 42%; GS: 34%, p < 0.001, d > 1.8), suggesting a highly dynamic style. Quasi-isometric mode was significantly longer on OL than IL in GS (34 vs. 20%, p < 0.001, d = 1.16) and SG (42 vs. 28%, p < 0.001, d = 1.11) but was significantly longer on IL than OL in SL (19 vs. 11%, p < 0.001, d = 0.64). Thus, GS and SG showed similarities, with a significantly faster knee eccentric mean angular velocity on IL compared to OL (GS −58 vs. −54°.s−1, SG −52 vs. −45°.s−1, p < 0.001, d ≥ 0.22) whereas SL showed an opposite pattern (−72 vs. −89°.s−1, p < 0.001, d = 1.10). The quasi-isometric phase was overlooked in previous studies but is crucial to consider. The current data may be used to train the outside and inside leg specificities incorporating discipline-specific contraction modes and exercises.
Highlights
The muscular work of the skier was historically described at slow angular velocity during knee flexion and extension phases (Berg et al, 1995)
Quasi-isometric mode was significantly longer on outside leg (OL) than inside leg (IL) in Giant Slalom (GS) (34 vs. 20%, p < 0.001, d = 1.16) and Super Giant (SG) (42 vs. 28%, p < 0.001, d = 1.11) but was significantly longer on IL than OL in SL (19 vs. 11%, p < 0.001, d = 0.64)
The hip concentric velocity on OL was higher in SL than GS (p = 0.020, large effect d = 1.12) and tended to be higher in SL than DH (p = 0.094, large effect d = 2.34), without differences on IL (p > 0.382, d ≤ 1.56, FIGURE 2 | 2D distribution of the knee angular position (y-axis) and velocity (x-axis) for Slalom (SL), Giant Slalom (GS), Super Giant (SG), and Downhill (DH)
Summary
The muscular work of the skier was historically described at slow angular velocity during knee flexion (eccentric work of the knee extensors) and extension phases (concentric work of the knee extensors) (Berg et al, 1995). Alpine Skiing Joint Kinematic of parabolic skis (carving) (Raschner et al, 2001). These developments have brought this eccentric predominance into question as quasi-isometric and concentric components have been described during carved turns (Kröll et al, 2015a; Minetti, 2016). It was suggested that the bi-articular rectus femoris maintained a nearly constant length in female practicing recreational ski whereas the vastus lateralis lengthened during the first phase of inside leg (IL) turn (eccentric work), shortened during the edge change phase (concentric work) and contracted isometrically on the subsequent outside leg (OL) phase (Kröll et al, 2010). The evolution in the joint kinematic aspects of the ski turn with ski carving has been described in Giant Slalom (GS) (Kröll et al, 2015a) but never in the speed disciplines
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