Introduction: Classical cross-country skiing (CSS) can be performed using three main techniques: diagonal stride (DS), double poling (DP), and double poling with kick (DK). In CSS, the mechanical external work (Wext) was recently estimated by Pellegrini et al. (2014) in skiers while they roller skied on a treadmill at 14 km/h (and a 2° slope) and found to be: 0.87, 0.70 and 0.79 J/m/kg for DS, DP and DK, respectively. In that paper, external work was calculated based on the kinetic and potential energy changes of CoM at each stride and by taking into account the work done to overcome frictional forces; however, in that study, the effects of air resistance (drag) on Wext was not investigated. The aim of this study was to estimate air resistance (at this slope and speed and in these three techniques) based on intracyclic measures of frontal area (as recently proposed by Gatta et al. 2015 in swimming). Methods: Four cross-country skiers (3M/1F) were asked to roller ski at 14 km/h (and a 2° slope) on a treadmill (H/P, Saturn 300/100r, Cosmos, Germany) using DS, DP and DK techniques. All trails were video-recorded with a camera (Elixim Casio, 100 Hz) positioned behind the skier. The ImageJ software was utilized to calculate frontal area (A) in five "positions" during the cycle (DS = left propulsive phase; rolling phase; right propulsive phase; rolling phase ; left propulsive phase; DP = pole contact; pole propulsion; propulsive phase; rolling phase; pole contact; DK = pole contact and propulsion; left propulsive phase; rolling phase; right propulsive phase; pole contact). Drag force was calculated by means of the pressure drag equation: Fd = 0,5·A·Cd·p·v2; where Cd = 1, p = 1.18 and A = average frontal area. Results: Average frontal area was 0.930±0.056, 0.987±0.139 and 0.928±0.134 m2 in DS, DP and DK, respectively. The intra-cyclic variations in A were 6.0±3.8, 12.5±6.5 and 6.7±1.7 % in DS, DP and DK. Fd was 7.46±0.45, 7.93±1.11 and 7.45±1.07 N in DS, DP and DK, respectively. Discussion: This is the first study (to our knowledge) that attempts to estimate drag resistance in CCS based on measured values of frontal area. The larger intracyclic variations were observed in DP (12.5%) whereas small differences were observed in the other two techniques (6-7%). In % of total external work (Wext + Fd) air resistance was of about 9-14%, in all techniques. This indicates that Fd could not be neglected when external mechanical work is calculated in this form of locomotion.
© Copyright 2016 21st Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Veröffentlicht von University of Vienna. Alle Rechte vorbehalten.