INTRODUCTION: There is a diversity of opinion among coaches as to where in a turn cycle skiers gain and lose speed. Knowing more about in which phases of the turn cycle a skier accelerates could lead to different technical and tactical approaches. The purpose of this study was to describe the time course of VCOM through a turn cycle. METHODS: In April 2006, the performances of 6 male members of the Norwegian Europa Cup team were analyzed through 2 turns during a race Simulation in Slalom. Skier 3-D positions were determined from 4 panning cameras and calibration control points distributed near the course (Nachbauer et al., 1996). COM turn radius (RCOM) at each time point was calculated as the radius of the arc passing through the 3 previous points, the current point, and the 3 following points. Instantaneous VCOM was calculated using first central differences. The turn cycle was divided into two phases based on RCOM: The turn phase (TP) and the straight phase (SP). TP start and end points were defined as the time points when RCQM decreased below 15m and increased above 15m, respectively. RESULTS & DISCUSSION: In examining the ensemble average of VCOM for the 12 analyzed turns (Figure 1), a cyclic pattern of positive and negative acceleration is readily apparent. The mean accelerations (± SD) in the SP and TP were 2.33 m/s2 (± 0.20) and -1.86 m/s2 (± 0.54), respectively. The results show a surprisingly strong relationship between the time course of VCOM and the turn cycle. Based on this knowledge, two approaches could be taken to improve performance: Reduce braking forces by skiing a longer, more carved TP, or shorten the TP and maximize the benefits of acceleration in the SP. CONCLUSIONS: The results of this study indicate that SP is where skiers increase VCOM and, conversely, TP is where VCOM is decreased. To what extent the same pattern will occur for turns with differing radii, or in turns on slopes of different inclinations, is yet to be determined.
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