Ergonomic analyses of downhill skiing

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Abstract
The purpose of this study was to provide electromyographic feedback for (1) pedagogical advice in motor learning, (2) the ergonomics of materials choice and (3) competition. For these purposes: (1) EMG data were collected for the Stem Christie, the Stem Turn and the Parallel Christie (three basic ski initiation drills) and verified for the complexity of patterns; (2) integrated EMG (iEMG) and linear envelopes (LEs) were analysed from standardized positions, motions and slopes using compact, soft and competition skis; (3) in a simulated ‘parallel special slalom’, the muscular activity pattern and intensity of excavated and flat snow conditions were compared. The EMG data from the three studies were collected on location in the French Alps (Tignes). The analog raw EMG was recorded on the slopes with a portable seven‐channel FM recorder (TEAC MR30) and with pre‐amplified bipolar surface electrodes supplied with a precision instrumentation amplifier (AD 524, Analog Devices, Norwood, USA). The raw signal was full‐wave rectified and enveloped using a moving average principle. This linear envelope was normalized according to the highest peak amplitude procedure per subject and was integrated in order to obtain a reference of muscular intensity. In the three studies and for all subjects (elite skiers : n=25 in studies 1 and 2, n = 6 in study 3), we found a high level of co‐contractions in the lower limb extensors and flexors, especially during the extension phase of the ski movement. The Stem Christie and the Parallel Christie showed higher levels of rhythmic movement (92 and 84%, respectively). The second initiation movement of the Stem Turn produced 74% repetitive rhythmic patterns. In addition, its coordination pattern was more complex. Systematic differences were noted between the racing, soft and compact skis. The comparison of LE patterns and of iEMG while skiing through flat and excavated, but identical slaloms (slope and distance), indicated no significant differences. These data suggest that (1) the Stem Turn demands a higher level of neuromuscular ability than the other two drills and it should therefore only be introduced in the training of more advanced skiers ; (2) on average and for the slope inclinations investigated (11° and 27°), the soft ski showed the least EMG activity, indicating that it allows better control of the overall ski movements; and (3) the excavated snow conditions in slalom competitions were not a disadvantage to the athletes.