Forward acceleration of the centre of mass during ski skating calculated from force and motion capture data

Abstract

The purpose of this paper was to present and evaluate a methodology to determine the contribution of bilateral leg and pole thrusts to forward acceleration of the centre of mass (COM) of cross-country skiers from multidimensional ground reaction forces and motion capture data. Nine highly skilled cross-country (XC) skiers performed leg skating and V2-alternate skating (V2A) under constant environmental conditions on snow, while ground reaction forces measured from ski bindings and poles and 3D motion with high-speed cameras were captured. COM acceleration determined from 3D motion analyses served as a reference and was compared to the results of the proposed methodology. The obtained values did not differ during the leg skating push-off, and force-time curves showed high similarity, with similarity coefficients (SC) [0.90 in the push-off and gliding phases. In V2A, leg and pole thrusts were shown to contribute 35.1 and 65.9% to the acceleration of the body, respectively. COM acceleration derived from ground reaction forces alone without considering the COM position overestimated the acceleration compared to data from motion analyses, with a mean difference of 17% (P \ 0.05) during leg push-off, although the shapes of force-time curves were similar (SC = 0.93). The proposed methodology was shown to be appropriate for determining the acceleration of XC skiers during leg skating push-off from multi-dimensional ground reaction forces and the COM position. It was demonstrated that both the COM position and ground reaction forces are needed to find the source of acceleration.

Drag Area, Frontal Area and Drag Coefficient in Cross-Country Skiing Techniques

“…This can be done by roller skiing on a treadmill in a wind tunnel [6], where the roller skis and ski poles are equipped with sensors to register resultant forces during the push-off phases. In order to calculate the overall propulsion and the separate propulsive forces produced by arms and legs, a high-speed 3D motion analysis system can be used to provide data like ski angle, edging angle, incline angle and center of mass position together with pole and leg forces [8]. Also, with knowledge of the rollers skis' rolling resistance and the gravity force, the residual force FD can easily be calculated.…”

Arm swing during skating at different skiing speeds affects skiing mechanics and performance

“…On the contralateral side, vertical and anterior‐posterior (along the ski) GRFs were collected (force binding 2). The force bindings and used procedures for calibration with special devices are described and pictured elsewhere . The anterior‐posterior component of GRF at the swing assisted push‐off side could not be directly derived and had to be estimated from data collected on the contralateral side using methods described in Göpfert et al …”

“…3D motion was recorded (100 Hz) with the Vicon Nexus motion capture system (Vicon, Oxford, UK) consisting of a 16 camera setup (T‐Series T40S) installed on a wooden frame at the ceiling inside the ski tunnel . The marker placement consisted of the Full Body Plug‐In Gait marker setup completed by markers on both trochanter major, mid sternum and mid spine as well as three markers on each ski.…”

“…Data were transmitted wireless (WLS‐9163; National Instruments, Austin, TX, USA) to a receiver‐card of a portable computer with a custom made data collection software (Labview 8.5; National Instruments). Participants wore a waist‐bag on the middle of the back with a total weight of 2590 g containing the necessary measurement equipment . An analogue trigger signal was simultaneously recorded by both data collection systems prior to each trial and used as sync peak for synchronizing data from force binding and motion capture data.…”

“…Centre of mass position was calculated from 3D motion capture data using the XC‐model . Further scripting (Body Language; Vicon) was used to determine the COM of the arms and the right and left arm's COM respectively.…”