| Objective: With the 2022 Winter Olympic Games,more attention is being paid to winter sports,and sitting cross-country skiing is included in the sports programme of the International Paralympic Winter Games,as well as being an official event of the Winter Paralympic Games.There is still a big gap between China’s competitiveness in sitting cross-country skiing and that of European countries,and the analysis of the specific physical and technical factors of sitting cross-country skiing double pole pushing in the Winter Paralympics is still in its infancy.Therefore,this study uses a three-dimensional motion capture system to film the sitting cross-country skiing movements,analyse the relationship between the maximum upper limb strength and skiing performance during sitting cross-country skiing,and investigate the influence of shoulder abduction angle on the biomechanics of sitting cross-country skiing,so as to explore the specific physical and technical factors affecting sitting cross-country skiing.Methods: This study selected Capital University of Physical Education and Sports undergraduate students as subjects for sit-skiing.Study 1 used an isokinetic muscle testing instrument to measure the upper limb’s maximum strength of the subjects and recorded the upper limb’s work data using a self-designed sit-skiing simulator,analyzing the correlation between the upper limb’s maximum strength and upper limb power output during the sit-skiing process.In Study 2,3D infrared motion capture technology and Open Sim modeling technology were used to analyze the impact of shoulder abduction technique on sit-skiing’s dynamic output and biomechanical characteristics.Results:(1)The study found a significant positive correlation between the distance of periodic sliding(?s)during seated cross-country skiing and the work done over 30 seconds and 3 minutes(r = 0.68,P < 0.01;r = 0.63,P < 0.01),indicating that the longer the distance traveled by the ski pole during a sliding cycle,the more work the pole does.During the later stage of pole support,the angle between the pole and the ground decreases,the horizontal component of the pole force increases,and the work efficiency significantly improves.Analysis of the periodic sliding time(?t)showed that the faster the sliding speed and the higher the frequency,the greater the work done by the ski pole(?t was significantly correlated with 3 minutes of work,r = 0.412,P < 0.05).(2)Significant correlations were found between the strength of the upper limb flexor and extensor muscle groups and the work done.The slow-speed strength of the shoulder muscle group(30° isometric strength)and the fast-speed strength of the elbow muscle group(120° isometric strength)were highly correlated with 3 minutes of work(r = 0.59,P < 0.001;r = 0.71,P < 0.001).Stepwise regression analysis showed that the 60°/s shoulder extension muscle strength accounted for 34% of the variance in the 30-second test,while in the 3-minute test,the 60°/s shoulder extension muscle strength accounted for about 40% of the variance.During the early stage of pole support,the shoulder joint extensor muscles,represented by the triceps brachii,are activated to generate force.At this time,the angle between the ski pole and the ground is large,and the work efficiency of the pole force is low,requiring a greater amount of shoulder strength to drive the sled.During the later stage of pole support,the angle between the ski pole and the ground decreases,the work efficiency of the pole force increases,and the sled can be pushed forward rapidly with smaller pole force,mainly driven by the fast-speed elbow muscles.(3)Using a larger shoulder abduction angle during seated cross-country skiing can result in a longer sliding distance(i.e.,at 24°(1.07 ± 0.12 m vs.1.02 ± 0.14 m,P =0.029)and 30°(1.11 ± 0.13 m vs.1.02 ± 0.14 m,P < 0.001)),as well as a greater output power(i.e.,compared with 0°,at 24°(610.94 ± 158.96 J,P = 0.011)and 30°(629.10 ±168.78 J,P < 0.001),the sliding performance is higher).Conclusions:(1)In skiing performance indicators,the longer the distance and the higher the frequency of a single cycle of pole support,the greater the output power of the upper limbs.Therefore,it is recommended that disabled skiers increase the distance of a single pole support cycle and the sliding frequency during pole support.In the technique of double-pole pushing in sit-skiing,the total contribution rate of the fast power of the shoulder flexor muscle group and the slow maximal power of the shoulder extensor muscle group to the output power of the upper limbs is 73.8%.It is recommended that disabled skiers strengthen the training of elbow flexor muscle group’s fast power and the shoulder extensor muscle group’s slow maximal power training.(2)When athletes use the shoulder abduction technique to slide,the output power increases,but the efficiency during sliding decreases.This means that choosing the best shoulder abduction angle may depend on the terrain or skiing speed.Specifically,it is recommended that sit-skiing athletes slide with a larger shoulder abduction angle during the starting or climbing stage.Shoulder abduction can help muscle exertion,and because the vertical component of the ski pole is larger and counteracts gravity,it is easier to drive the sled.On flat terrain,it is recommended that athletes use a smaller shoulder abduction angle during pole support,and the effective output power during sliding will be greater,making it easier to push forward. |
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