ABSTRACT
Under the background of technological assistance to prepare for the Beijing Winter Olympics in China, the biomechanical research highlights and the latest achievements related to competitive performance of alpine skiers in recent years were systematically analyzed in this paper, so as to determine biomechanical factors affecting competitive performance of alpine skiers, including aerodynamic drag, frictional forces, ground reaction force (GRF), energy dissipation, turn radius, trajectory of the skis and/or center of mass (COM). In addition, biomechanical differences in turn techniques, multiple turns connections and abilities of individuals were also considered as important factors affecting the alpine skiing performance. In the case of slalom and giant slalom events, the earlier initiation of turns, longer path length and trajectory, earlier and smoother application of GRF, and carbene technique carving to reduce the ski-snow friction and thereby dissipate energy should be used to improve sports performance. During speed skiing, minimizing the exposed frontal area and positioning the arms close to the body can reduce the energy loss caused by aerodynamic drag, thereby improving sports performance. Top-level alpine skiers will always perform well on different courses, terrains and snow conditions during the race. Excellent alpine ski performance from a biomechanical perspective includes the efficient use of potential energy, minimizing ski-snow friction and aerodynamic drag, choosing optimal trajectory and maintaining high-speed skiing. Individual tactics and techniques should be valued in training and competition. For better results, the same performance on multiple sections and on different terrains is more important than excellence in individual sections and specific conditions.
ABSTRACT
Objective To explore the effects of notoginsenoside-Rg_1 on brain-derived neurotrophic factor(BDNF) protein in cerebrum cortex of MCAO/R injury,as well as to investigate whether notoginsenoside-Rg_1 can up-regulate the protein content of BDNF of the positive neurons or the amount of the po-sitive neurons.Methods Adult male SD rats(60) were randomly divided into model group,notoginsenoside-Rg_1 high,middle,and low dose(200,100,50 mg/kg) groups,and the positive control(Nimodipine,1 mg/kg) group.All drugs were given once a day by ip till the mouse was killed.The focal cerebral(ischemia-)reperfusion model was made with thread-occluded method.Their frozen brain tissue were sliced(into) section of 12 ?m thickness.The four rats were randomly taken from each groups to be treated as specimens after surgical handle in 1,3,and 7 d.The slices were according to the immunohistochemical ABC techniques.The protein content of BDNF of the positive neurons and the amount of the positive neurons in cerebrum cortex of rat were observed and counted by HPIAS—1000 analytic system,and the nervous deficit symptoms after the cerebral ischemia were observed.Results Comparing with the model group,all notoginsenoside-Rg_1 treated groups obviously improved some nervous deficit symptoms of cerebral ischemia-reperfusion rats,and increased the protein content of BDNF and the amount of the positive neurons in the cerebrum cortex of model rats(P