Biomechanical Characteristic Of The Lower Limb Technique Of Push Of Chinese Elite Skeleton Athletes

Purposes:This study investigated the kinematic,kinetic and electromyographic characteristics of the lower limb technique of the push during the acceleration and maximum speed phases on land and the kinematic characteristics of the entire push on ice,and attempts to analyse the lower limb technique of Chinese athletes of different push skill level,in order to provide a basis for improving the theoretical system of skeleton sport,to scientifically guide the physical training and push technique training of skeleton athletes,and to provide a scientific guarantee for Chinese skeleton team to achieve the expected goal in the 2022 Beijing Winter Olympic Games.Methods:In this study,18 athletes(10 men and 8 women)from Chinese skeleton national team were selected as test subjects and a combination of land and ice push techniques was adopted.The kinematics,kinetics and electromyography of the lower limb of the push technique at acceleration phase and maximum speed phase on land-push and the kinematic characteristics of the lower limb of the first 30 m of the push technique on ice were investigated.In addition,the land-push was divided by speed while ice push was divided by start time to explore the differences between the athletes at different push skill levels on land and ice respectively.Pearson correlation analysis was used to analyse the relationship between land-push speed and ice push performance;statistically analysis of kinematic,kinetic and electromyographic data at acceleration phase and maximum speed phase on the land push was performed using a paired samples t-test with a significance level of p<0.05.Grey correlation analysis was used to analyse kinematic indicators affecting the push sled technique.Results:(1)There is a very strong negative correlation between velocity at acceleration phase and maximum speed phase and push time on ice(r=-0.83;r=-0.85;p<0.05),the faster the velocity at acceleration phase and maximum speed phase,the shorter the push time on ice,i.e.the better the ice performance.(2)For the land-based push:(1)The kinematic indicators that correlated well with the horizontal speed of the center of gravity at acceleration phase were toe-off distance,hip range of motion in the early swing and propulsion phase,knee angle at touchdown and at the end of the braking phase,hip angle at the end of the early swing phase,ankle angle at the end of the propulsion phase and stride length.The top kinematic indicators associated with horizontal speed of the center of gravity at maximum speed phase were touchdown angle,stride frequency,stride length,hip range of motion in the early swing and propulsion phase,toe-off distance,toe-off angle and duration of the swing phase.(2)The faster male athletes had smaller peak braking force,smaller peak propulsion force and larger peak vertical force at acceleration phase,and larger peak braking force,peak propulsion force and peak vertical force at maximum speed phase.The faster female athletes had smaller peak braking and vertical forces and larger peak propulsion forces at acceleration phase,and larger peak braking and propulsion forces and smaller peak vertical force at maximum speed phase.(3)The hip flexors do mainly centripetal contractions with positive power in the early swing phase while hip extensors do mainly centripetal contractions with positive power in the later swing phase and braking phase,but from the propulsion phase onward,the hip flexors do centrifugal contractions with negative power.The knee extensors do mainly centrifugal contractions with negative power in the anterior swing phase while the knee flexors do mainly centripetal contractions with negative power in the later swing phase and braking phases,and the knee extensors do mainly centripetal contractions with positive power in the propulsion phase;the ankle muscles produced negligible power in the early swing and later swing phases,the plantar flexors do mainly centrifugal contractions with negative power in the braking phase,and switched to centripetal contractions with positive power at about 30% of the propulsion phase.(3)For the Ice push: the male athletes with better push performance have a relatively low step velocity in the first 7 steps and a higher step velocity thereafter,but a relatively low percentage of their maximum velocity until the last step before loading.The female athletes with better push performance have higher step velocity in almost all steps up to the 3 steps before loading.Conclusions:(1)Faster stride frequency,shorter stride length,shorter support times,larger touchdown angle,smaller toe-off angle,actively thigh swing and stretch,and full lower limb extension are more conducive to increasing the pushing speed during acceleration phase,while faster stride frequency,longer stride length,shorter support times,smaller touchdown angle,larger toe-off angle,and less excessive lower limb extension are more conducive to pushing speed during the maximum speed phase.(2)Improving or optimising the push technique should produce as much propulsion as possible and focus on a good ratio of braking force to propulsive force,which is especially important for obtaining maximum pushing speed.(3)The hip flexors are the main source of power during the early swing phase,while the hip extensors are the main source of power during the later swing phase and braking phase;during the propulsion phase,the knee extensors and the plantar flexors are the main source of power.(4)The athletes with better push results had relatively slower step velocity in the early stages of pushing,progressively faster step velocity in the middle stages of pushing,and significantly faster step velocity in the end stages of pushing.