To our knowledge, this study is the first to analyze air drag and lift in snowboard. Until now, modeling of BA and slopestyle jumps were performed using cDA values from alpine skiing. This study showed that cDA issued from alpine skiing studies (ranging from 0.25 to 0.5 m2 for giant slalom,34Meyer F. Le Pelley D. Borrani F. Aerodynamic drag modeling of Alpine skiers performing giant slalom turns. and 0.15 m2 for downhill discipline35Barelle C. Ruby A. Tavernier M. Experimental model of the aerodynamic drag coefficient in alpine skiing.) underestimated the true cDA for BA and slopestyle.Due to the current lack of any comparable data and the fact that regular apparel is most frequently worn during elite level competitions36Wolfsperger F. Meyer F. Guillaume S.G.M. Towards more valid simulations of slopestyle and big air jumps. (observations of 163 athletes at FIS World Cup at Seiser Alm 2018; Fig. A2), we are convinced that the models derived in this study provide a useful contribution to improve the understanding and modeling of in-run mechanics in slopestyle and BA. For skiers and snowboarders, wearing regular fit apparel, posture-dependent formulations were deduced for cDA and cLA. The speed dependency of cDA was largely significant in the individual models, but not consistent in direction, and had smaller effect than apparel and posture. For skiers in mid and extended posture the cDA was mostly negatively related with speed, which corresponds to findings on alpine skiers,37Elfmark O. Reid R. Bardal L.M. Blockage correction and Reynolds number dependency of an Alpine skier: a comparison between two closed-section wind tunnels. whereas for snowboarders all significant relations of cDA with speed, were positive. This discrepancy might be caused by the different inflow (frontal vs. lateral) affecting the Reynolds Number range or slight changes of posture at higher speeds.37Elfmark O. Reid R. Bardal L.M. Blockage correction and Reynolds number dependency of an Alpine skier: a comparison between two closed-section wind tunnels. As speed effects were small compared to the other factors influencing cDA in the in-run, these were neglected in our model.15McNeil J.A. Hubbard M. Swedberg A. Designing tomorrows snow park jump.,19Schindelwig K. Platzer H.P. Mössner M. et al.Safety recommendations of winter terrain park jumps into airbags. We suggest that course builders use the posture-dependent models (Eqs. (3), (4), A1 and A2) to simulate an average in-run, and the individual, apparel and posture-dependent data (Fig. 3, Tables A1 & A2) as estimates for extreme aerodynamic coefficients. Course builders need to build jumps that allow for a certain range of speed at take-off, with a critical lower limit of take-off speed. However, this lower limit is not sharp, since it changes with external conditions and user groups. Therefore, a certain range is needed to compensate for headwind, snow conditions and differences in mass between sexes and snow friction between snowboards and skis. If in-run speed is at the low end, athletes have some capacity to compensate for this by pushing off at the start and reducing air drag by choosing a low posture during the in-run. This study shows that the capacity to compensate for limited speed in the in-run is substantially smaller for snowboarders than for skiers as the range of cDA for realistic postures is about tripled for skiers compared to snowboarders and minimum cDAs of skiers are approximately 0.1 m2 smaller than of snowboarders. The reason for this difference may be that snowboarders' balance setting allows them to manipulate hext only in a small range compared to skiers. In addition, squatting does not lead to overlapping of body segments, and consequently does not affect the frontal area as it does in skiing. However, snowboarders should be aware that upper body orientation has a strong influence on the cDA, and can be used to reduce air drag when speed is critical. As more and more high-level competitions are held using the same course for males and females, ski and snowboard course construction should pay particular attention to snowboarders' limited ability to compensate for head winds and elevated snow friction using alterations in body posture. However, this study also shows that athletes can substantially reduce air drag with their choice of apparel, if take-off speed is critical: Wearing wide fit apparel compared to slim fit increased cDA as much as changing from the mid to the extended posture for skiers and changing to the extended rotated posture for snowboarders (Fig. 2).

For modeling of the flight phase, this study contributed the first values for drag and lift. For compact posture holding a grab, we recommend using rounded averages over all tested inflow directions for cDA and cLA of 0.44 m2 and 0.09 m2 for skiers, and 0.40 m2 and 0.04 m2 for snowboarders. Although the results show distinct differences depending on the inflow direction, we consider averaging from 0° to 180° is reasonable, as athletes mostly aim to rotate full numbers of semi twists.

The limitations of the test design included the small number of athletes, the lack of small and female athletes as well as a rather rough quantification of the apparel fit. The number and choice of athletes was constrained by the financial means for wind tunnel testing and the fact, that the athletes tested in the wind tunnel were included in a second study on snow friction, where the individual air drag values from wind tunnel testing were applied to distinguish air drag and snow friction for these athletes. Although the tested athletes did not represent the overall population of slopestyle and BA athletes, the test efficiency was kept as high as possible within the study's financial limits.