CC BY
32UDC 796.922
Biomechanical characteristics of v1 skate technique of elite Nordic combined skiers
PhD N.B. Novikova1 G.G. Zakharov1 Dr.Biol. A.V. Voronov2
1St. Petersburg Scientific Research Institute of Physical Culture, St. Petersburg
2 Federal Scientific Center for Physical Culture and Sports, Moscow
Corresponding author: [email protected]
Abstract
Objective of the study was to analyze the V1 skate ski double poling competitive techniques of the world Nordic combined elite.
Methods and structure of the study. We analyzed the video recordings of ski techniques of 20 Nordic combined skiers, who had demonstrated the best results in the ski race by the Gundersen method at the world championship. We determined the speed of movement, stride length and frequency, angular and spatial characteristics of ski technique in the 10 km pursuit race, as well as the dynamics of indicators on the four distance laps.
Results and conclusions. The study found the following specifics of the skate ski double poling techniques of the leading Nordic combined competitors: the lower leg to the surface angle is kept under 60° to facilitate the body center of mass push forward at the sub-squatting moment; asymmetric double poling move by arms and legs to maintain the run speed by rather a wider stride than special kick-off efforts; shoulders are turned when leaning on the poles towards the support leg for the stride effectiveness at some sacrifice for the poling effort efficiency; relatively even pace on the distance with the speed acceleration on the last lap mostly due to the pace being increased; and the cross-country skiing race time was found largely determined by the run speed on ascends and stride on every lap. The study data and findings are recommended to be taken into account by the Russian Nordic combined training system updating projects. Further comparative studies of the world strongest Nordic combined competitors' racing techniques are recommended.
Keywords: Nordic combined, V1 skate ski double poling, kinematics, biomechanics, ski jumping, cross-country skiing, body center of mass.
Background. Nordic combined events include different cross-country skiing formats with the athletes' positions determined by the prior ski jumping results. Traditionally, special attention is given to the ranking ski jumping events, whilst the cross-country skiing techniques are rated second and, hence, still under-explored [1]. Traditional cross-country skiing training in Nordic combined largely mimics modern crosscountry skiing techniques in spite of the fact that the Nordic-combined-specific motor skills and fitness requirements are significantly different from the classical cross-country skiing.
As reported by some Scandinavian researchers, annual training time of highly skilled Nordic combined
competitors average 836 hours with 52%, 3% and 5% of the low-, moderate- and high-intensity crosscountry skiing and 40% of the strength, speed and ski jumping skills trainings [3]. Most of the Nordic combined and cross-country skiing trainings are kept within Intensity Zone I as required by the popular 75-5-20 "polarized training" system [4]. It should be noted that total aerobic trainings in the modern cross-country skiing sport average much higher than in the Nordic combined: 646 hours versus 435 hours.
Russian sources provide little if any data on the training workloads of the Nordic combined elite. Thus Ser-geev et al. report the total cyclic training workloads varying under 60% for the cross-country skiing elite, with the
Table 1. Averaged skate ski double poling technique biomechanics of the top-20 Nordic combined competitors on the 10 km pursuit cross-country skiing scoreboard, n=20
Lap Value Speed, m/s Stride, m Cycle time, s Pace, cycles/ min Kick-off time, s
1 Average 2,95 3,40 1,16 51,99 0,32
S 0,25 0,19 0,07 2,92 0,04
2 Average 3,04 3,45 1,14 52,80 0,31
S 0,25 0,18 0,05 2,56 0,04
3 Average 2,88 3,20 1,12 54,10 0,31
S 0,24 0,22 0,08 4,13 0,04
4 Average 3,33 3,40 1,03 58,80 0,29
S 0,43 0,25 0,11 6,67 0,04
low-intensity and short aerobic workloads estimated at only 23-40% of the cyclic training workloads [2].
Furthermore, Nordic combined training systems assign much time to the ski jumping trainings with a special stringent requirements to the body mass indices and diets. Presently the valid FIS rules set a low-limit threshold for the body mass index - and this is only one of the reasons why the cross-country skiing techniques in Nordic combined have their specifics. We believe that an analysis of the crosscountry skiing techniques biomechanics of the world Nordic combined elite may be helpful for the national Nordic combined training systems excelling purposes.
Objective of the study was to analyze the V1 skate ski double poling competitive techniques of the world Nordic combined elite.
Methods and structure of the study. The study data were collected at the 2019 World Championships in Seefeld (Austria). In the Individual Gundersen cross-country skiing event, the athletes run 10 km (four 2.5 km laps) pursuit in free style, with the starting numbers and time disadvantages ranked according to the ski jumping scores. We captured the cross-country skiing techniques on the key 370 m long 4°ascend by a Sony HDR730 video camera fixed on top of the slope perpendicular to the track; plus the same side-view moving video camera for the skate ski double poling technique recording and analyzing purposes. The skate ski double poling technique biomechanics were
then processed and analyzed by Dartfish Pro Sute 7 software toolkit.
Results and discussion. The cross-country skiing techniques of the Nordic combined elite were tested to rate the momentary speed on ascend, movement frequency (pace), stride (elementary length of a movement cycle), kick-off time; and the joint angels in the low point (sub-squat phase) of the cycle. Given in Table 1 hereunder are the averaged cross-country skiing technique biomechanics of the top-20 competitors on the cross-country skiing event scoreboard.
Run speed of the top-20 competitors on the ascend was found to average 2.95 m/s on Lap 1, slightly grow on Lap 2, then somewhat fall on Lap 3 (versus the Lap 1), and come to the maximum of 3.33 m/s (12.9% growth versus Lap 1 with p<0.01) on Lap 4. On the whole the athletes demonstrated fairly even and economic speed management on the distance with expressed finishing spurts. The final-lap skate ski double poling technique was different in the shorter and sharper kick-offs up to leaps in the finishing acceleration phase.
The speed sag on Lap 3 was associated with the stride length falling (Figure 1), although the pace was tested to gradually grow on the whole distance, especially in the finish spurt phase. Such correlation of the stride length with pace is generally typical for a growing muscular fatigue offset by the higher-intensity pacing efforts. Of special interest for analysis was the correlation of the pursuit race technique biomechanics
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Figure 1. Stride to pace correlation curve for the 10 km pursuit cross-country skiing event
Figure 2. Correlations of the laps-specific race speeds, strides and paces with the total race times for the top-20 competitors
Theory and Practice of Physical Culture I teoriya.ru I July № 7 2020
Table 2. Average joint angles in the sub-squatting point in the 10 km pursuit race, degrees
Lap Value Knee joint angle Ankle joint angle Thigh joint angle
1 Average 112,63 57,59 92,55
S 5,23 3,20 4,78
2 Average 109,34 56,79 90,04
S 6,02 3,61 5,12
3 Average 112,94 56,58 89,84
S 4,98 3,24 5,17
4 Average 109,99 54,59 82,11
S 5,36 3,36 5,24
with the pure race times. Given on Figure 2 are the correlations of the laps-specific race speeds, strides and paces with the total race times. We found that the most successful in the race were the athletes with the highest run speeds on ascend and longest strides, whilst the movement pace was in a significant correlation with the race time on the whole (it was tested significant for Lap 2 only).
The skate ski double poling technique biomechanics tests included joint angles metering with a special priority to the lowest point (sub-squatting) positions when the body mass and shin (knee position versus the toe) are shifted forward. Given in Table 2 are the joint angles in sub-squatting phase for the top-20 cross-country skiing competitors on every lap. The shin-to-ground angles were found to vary under 60° to facilitate the body center of mass pushing forward by the knee joint is in the top-flexion position. The Nordic combined elite knee and ankle joint angles were found to have no significant differences with the cross-country skiing elite. The torso to thigh angle was found to depend on the torso tilt angle and thigh position. The thigh angle was found to significantly (by 11.3%) fall on the final lap, with the torso tilt growing - that may be indicative of the high fatigue.
Having analyzed the top-20 Nordic combined competitors' cross-country skiing technique biomechanics, we found the following technical specifics. The double poling movement was found asymmetric, although arm bent remains virtually the same when the poles touch the ground to avoid losses. The shoulders remain turned to somewhat reduce the pressure on poles and facilitate the poling move at some sacrifice for its effectiveness. The lower is the individual strength the higher is the torso twist. Legs make a wide stride (lunge) with the lower leg highly tilt to facilitate the body center of mass being moved forward. The lead leg kick-off was tested active and strong with the other leg kicking off smoothly, without a special effort. The cross-country skiing race leaders were found to keep the movement technique stable all over the distance to save resource for the movement pace and kick-off strength increase in finishing acceleration phase.
Conclusion. The study found the following specifics of the skate ski double poling techniques of the
leading Nordic combined competitors: the lower leg to the surface angle is kept under 60° to facilitate the body center of mass push forward at the sub-squatting moment; asymmetric double poling move by arms and legs to maintain the run speed by rather a wider stride than special kick-off efforts; shoulders are turned when leaning on the poles towards the support leg for the stride effectiveness at some sacrifice for the poling effort efficiency; relatively even pace on the distance with the speed acceleration on the last lap mostly due to the pace being increased; and the cross-country skiing race time was found largely determined by the run speed on ascends and stride on every lap. The study data and findings are recommended to be taken into account by the Russian Nordic combined training system updating projects. Further comparative studies of the world strongest Nordic combined competitors' racing techniques are recommended.
References
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