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INTRODUCTION: Research investigating the correlation between impairment and key performance indicators in para-alpine skiing is needed for a future evidence based classification system (Tweedy and Vanlandewijck 2011). Only a little research in para-alpine skiing exists, especially in the standing classes LW5/7 and LW6/8 (impairment of one or two arms). The use of arms and poles affects performance in alpine skiing[OM1]  but how underlying biomechanical parameters as kinematics and kinetics are related to performance has to the authors knowledge not been studied before.

PURPOSE: The purpose of this study was to further the understanding of slalom skiing with two ski poles, one pole or without poles (c2, c1, c0) by investigating the biomechanical differences (kinematics and foot plantar pressure) for able-bodied athletes.

METHODS: Ten able-bodied right-handed junior skiers on national level were tested in three conditions - c0, c1, c2, while skiing a slalom course (28 gates, 62 m vertical drop). 3D kinematic data were collected at 200 Hz by 12 inertial motion units (Myomotion, Noraxon Inc, USA) placed on head, trunk, pelvis, arms and legs. Ski-time was measured with timing gates (XS Crystal Synchronization, Brower Timing Systems, USA) and kinetics were measured with pressure insoles (Pedar, Novel GmbH, Germany) placed inside each ski boot. Normal ground reaction force (nGRF) and relative force time integrals (relFTI) were calculated according to Melai et. Al (2011). Kinematics and plantar pressure were analysed over three right and left turns and averaged for each condition. Right turn and left turn were distinguished at the time point where the shank was standing vertical.

RESULTS: Time analysis showed that time increased with the use of less ski poles, mean difference between c1c2 of 1.27 ± 1.69 s (p=0.001) and between c0c1 of 0.73 ± 1.95 s (p=0.003[OM2] ). Kinematic analysis showed that different approaches were used to attack a slalom gate in condition c1 and c0, for example slalom-attack, giant slalom attack or opposite arm attack. Interquartile range and median of the body angles [OM3] differed between conditions, e.g. lower median (indicate less deviation from anatomical  basic position[OM4] ) in c0 and mostly lower than in c1 and c2. Furthermore, relFTI was related to the turning side (right or left turn) and showed largest asymmetry for condition c1.

CONCLUSION: Reduced balance due to missing ski pole/s lead to compensatory movements in the upper body and asymmetry in foot plantar pressure. This reduced the ability for a controlled turn. Whether or not only reduced balance or also the skiers low experience of skiing with reduced number of poles influenced the performance remains unclear.

REFERENCES

Melai, Tom, T. Herman IJzerman, Nicolaas C. Schaper, Ton L.H. de Lange, Paul J.B. Willems, Kenneth Meijer, Aloysius G. Lieverse, and Hans H.C.M. Savelberg. 2011. ‘Calculation of Plantar Pressure Time Integral, an Alternative Approach’. Gait & Posture 34 (3): 379–83. https://doi.org/10.1016/j.gaitpost.2011.06.005.

Tweedy, S. M., and Y. C. Vanlandewijck. 2011. ‘International Paralympic Committee Position Stand--Background and Scientific Principles of Classification in Paralympic Sport’. British Journal of Sports Medicine 45 (4): 259–69. https://doi.org/10.1136/bjsm.2009.065060.