PhD, Department Head N.B. Novikova¹
Researcher G.G. Zakharov¹
Researcher I.G. Ivanova¹
PhD, Department Head A.I. Golovachev²
PhD, Department Head A.V. Kubeev^2
1Saint-Petersburg scientific-research institute for physical culture, Saint-Petersburg
²Federal Science Center for Physical Culture and Sports, Moscow

Corresponding author: novik-nat@mail.ru

Keywords: cross-country skiing, tactics, skiathlon, macro-kinematics, competitive performance, elite cross-country skiers.

Abstract

Objective of the study was to analyze the competitive performance of the world skiathlon leaders in the 2021 World Ski Cup.

Methods and structure of the study. Subject to the study was the 30km skiathlon event of the World Nordic Ski Cup in Obersdorf (Germany) in January 2020. We shot the competitive performance videos on a 10° ascent in a key point of the eight loops by a video cam fixed on a tripod perpendicular to the track. The video captures were processed and analyzed using the DartfishPro 9 software toolkit to obtain the individual ascension speed, stride length, frequency and kick-off time for the 25 world strongest skiathletes. We also analyzed the individual time/ speed in every track section versus the terrain conditions, with the speed profiles verified by the formal competitive reports and analyses, including the detailed event statistics.

Results and conclusion. The middle-distance (2.3km) video captures yielded the ski stride macro-kinematics variation data including stride length, frequency and speed on ascend for each of the 25 competitors. The speed-ups in the final loops were associated with growth of the stride length plus insignificant growth of the movement frequency. The stride length was found correlated with the speed in agreement with the study data by Stögg l.T., Pellegrini B. and Holmberg H.C. (2018) [7], although we would emphasize importance of the kick-off power growth in the final spurt. This aspect should be taken into consideration by the training systems designers since growth in the stride length is secured by the kick-off power that require high muscular endurance.

Of special interest was the macro-kinematics analysis of the race leaders versus outsiders.

The skiathlon leaders’ racing tactics profiled by the macro-kinematics analysis provides an insight into the individual speed control patterns. We found the speed significantly falling on ascends in the skating-stride loops five and six and growing in the final loop. The race outsiders ranked 11-20^th on the event scoreboard were tested with the lower speed variations, although their speed and stride length in loop six were tested higher than the leaders’ ones. The ascension speed was tested to grow in both the leaders and outsiders groups. We found the individual speed and kick-off power acceleration resource mobilized in the final loops being critical for success in the race. We recommend the study data and findings for application in the precompetitive training systems by the potential qualifiers for the 2021 World Ski Cup.

Background. Competitive success in the top-ranking cross-country skiing events is known to depend not only on the individual motor skills, gifts and experiences but also on the skiing tactics including own competitive resource management and opposition control tools and the technical performance scenarios customizable to the track/ weather conditions, terrains etc. [2, 3]. Analysis of the modern study reports on the subject demonstrate the growing role of the cross-country skiing tactics in elite competitions due to the rapidly growing rivalry, new competitive formats, rules and challenges [4, 5, 6]. Modern long-distance cross-country skiing events with the hard terrains, widely varied weather and track conditions and multiple other factors of influence require highly efficient and versatile tactics for success [1].

Most of the researchers underline popularity of the positive resource management version that implies the athletes gradually decreasing the racing speed after the startup spurt [7]. In the mass competitions and pursuit races, the cross-country skiing tactics will always be customized to the terrains, track conditions, ski waxing specifics and, last but not least, the opponent tactics. Thus, the ski stride is ranked among the key success factors on ascends, whilst the stride frequency is deemed secondary by most of the cross-country skiing analysts. The distance speed analyses tend to prioritize the terrains, weather conditions and ski waxing specifics among the other important aspects [7].

Objective of the study was to analyze the competitive performance of the world skiathlon leaders in the 2021 World Ski Cup.

Methods and structure of the study. Subject to the study was the 30km skiathlon event of the World Nordic Ski Cup in Obersdorf (Germany) in January 2020. We shot the competitive performance videos on a 10° ascent in a key point of the eight loops by a video cam fixed on a tripod perpendicular to the track. The video captures were processed and analyzed using the DartfishPro 9 software toolkit to obtain the individual ascension speed, stride length, frequency and kick-off time for the 25 world strongest skiathletes. We also analyzed the individual time/ speed in every track section versus the terrain conditions, with the speed profiles verified by the formal competitive reports and analyses, including the detailed event statistics.

Results and discussion. To find and analyze the individual best skiing tactics on the distance, we made a statistical analysis of the individual average speeds in three track sections – basically flat (with minor irregularities), ascending and descending ones.

To find contributions of the sectional speeds into the competitive results, we input them as predictors in a linear regression equation to obtain the normalized linear regression rates: see Figure 1. As demonstrated by the Figure, the highest linear regression rates correlate with the final results – that means that the fastest sectional speeds heavily contributed to the competitive success. It should be emphasized that the descending speeds and ski replacement times had virtually no effect on the final individual ranks on the event scoreboard. We found the highest contribution to the final result of the first section speed (relatively flat terrain with a minor ascend), plus the steep ascend time in the final loop.

Figure 1. Sectional speed contributions to the final result in the 30km skiathlon World Cup event in Obersdorf, n=30

Given on Figure 2 are the individual sectional speed variations. The first-section speed (flat track with minor irregularities) was found to vary in a wavelike manner in the race, with some growth when the stride was changed and falls in the final loops. The speed variation range in this section (the gap between the fastest and slowest loop speeds) was estimated at 10.9%.

In the long ascending middle section of the track, the speed was increased in the second and fourth classic-stride loops – apparently due to the bonus points and tactical speed-ups. In the skating-stride skiathlon phase, the speed was growing with every loop to peak in the finishing span, with the speed increment in the final loop versus the prior one estimated at 9.9%. In the last loop sections (mostly on descends and final ascend) we tested significant speed sags in loops three and four – probably due to the lost ski slide in the classical style. In loop five the sectional speed was tested to grow due to the non-waxed skating stride advantage, with the speed increment in the skating phase (loops six through eight) estimated at 7.2% due to the final spurt on the last ascend and in the finishing span.

Figure 2. Averaged sectional speeds of the leaders in the 30km skiathlon World Cup event in Obersdorf, n=10

The middle-distance (2.3km) video captures yielded the ski stride macro-kinematics variation data including stride length, frequency and speed on ascend for each of the 25 competitors. The speed-ups in the final loops were associated with growth of the stride length plus insignificant growth of the movement frequency. The stride length was found correlated with the speed in agreement with the study data by Stögg l.T., Pellegrini B. and Holmberg H.C. (2018) [7], although we would emphasize importance of the kick-off power growth in the final spurt. This aspect should be taken into consideration by the training systems designers since growth in the stride length is secured by the kick-off power that require high muscular endurance.

Of special interest was the macro-kinematics analysis of the race leaders versus outsiders. We provisionally ranked with the leaders and outsiders the top-10 and the 11-20^th competitors on the event scoreboard, respectively. Their individual speed and stride length profiles provide an insight into their competitive tactics with accelerations and slow-downs (see Figure 3).

Figure 3. Individual speed and stride length variation profiles for the race leaders (n=10) and outsiders (n=10), with differences ranked by the Kruskal-Wallis criterion (* p≤0,05, ** p≤0,01, *** p≤0,001)

Conclusion. The skiathlon leaders’ racing tactics profiled by the macro-kinematics analysis provides an insight into the individual speed control patterns. We found the speed significantly falling on ascends in the skating-stride loops five and six and growing in the final loop. The race outsiders ranked 11-20^th on the event scoreboard were tested with the lower speed variations, although their speed and stride length in loop six were tested higher than the leaders’ ones. The ascension speed was tested to grow in both the leaders and outsiders groups. We found the individual speed and kick-off power acceleration resource mobilized in the final loops being critical for success in the race. We recommend the study data and findings for application in the precompetitive training systems by the potential qualifiers for the 2021 World Ski Cup.

References

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