Kinematic characteristics of elite men's 50 km race walking

Abstract

Race walking is an endurance event which also requires great technical ability, particularly with respect to its two distinguishing rules. The 50 km race walk is the longest event in the athletics programme at the Olympic Games. The aims of this observational study were to identify the important kinematic variables in elite men's 50 km race walking, and to measure variation in those variables at different distances. Thirty men were analysed from video data recorded during a World Race Walking Cup competition. Video data were also recorded at four distances during the European Cup Race Walking and 12 men analysed from these data. Two camcorders (50 Hz) recorded at each race for 3D analysis. The results of this study showed that walking speed was associated with both step length (r=0.54,P=0.002) and cadence (r=0.58,P=0.001). While placing the foot further ahead of the body at heel strike was associated with greater step lengths (r=0.45,P=0.013), it was also negatively associated with cadence (r= ?0.62,P<0.001). In the World Cup, knee angles ranged between 175 and 186° at initial contact and between 180 and 195° at midstance. During the European Cup, walking speed decreased significantly (F=9.35,P=0.002), mostly due to a decrease in step length between 38.5 and 48.5 km (t=8.59,P=0.014). From this study, it would appear that the key areas a 50 km race walker must develop and coordinate are step length and cadence, although it is also important to ensure legal walking technique is maintained with the onset of fatigue.     

Prophylactic effect of hot pack on symptoms of eccentric exercise-induced muscle damage of the wrist extensors

Abstract

This study investigated whether hot pack treatment could provide prophylactic effects on muscle damage induced by eccentric exercise of the wrist extensors. Twenty-eight healthy men (age 21±1 years, weight 65±16 kg, height 171±6 cm) were randomly placed into hot pack (n = 14) and control (n = 14) groups. All participants performed an exercise consisting of 300 maximal eccentric contractions of the wrist extensors of the non-dominant arm using an isokinetic dynamometer. A hot pack was applied for 20 min to the wrist extensors of the exercised arm before the exercise for the hot pack group. The control group received no treatment before the exercise. Measured variables included pain intensity assessed by a visual analogue scale and a modified Likert's scale, cold thermal pain threshold, pressure pain threshold (PPT), range of motion in active wrist flexion (ROM-AF) and extension (ROM-AE), range of motion in passive wrist flexion (ROM-PF) and extension (ROM-PE), grip strength, and wrist extension strength. Changes in these variables before, immediately after, and 1 to 8 days following the exercise were compared between groups by a two-way repeated measures ANOVA. All outcome measures from both groups (except for the cold thermal pain threshold of the hot pack group) demonstrated a significant change within the first 2–3 days following exercise. Significant differences between groups were only found at a single point in time for PPT, ROM-PF, ROM-PE and ROM-AE, and the changes were smaller for the hot pack group in comparison to the control group. These results suggest that the prophylactic effects of hot pack treatment on eccentric exercise-induced muscle damage of the wrist extensors are limited.     

Acute effects of vibration-assisted stretching are more evident in the non-dominant limb

Abstract

The aim of this study was to investigate the acute effects of a vibration-assisted static stretching intervention on enhancing split range of motion in gymnasts matched on initial range of motion. Twenty-two female artistic gymnasts (mean age 13.8 years, s=2.3) matched for age (±6 months) and competitive level were randomly assigned to a static stretching intervention with or without simultaneous vibration. The test consisted of adopting a forward split position with the rear leg bent to 90° and held vertically against a matted block while the pelvis remained perpendicular to the lines of the two legs. The gymnast was instructed to descend into the lowest split position of her comfortable pain tolerance. Positions were videotaped and digitized creating an angle between the split legs. The stretching intervention consisted of a forward split position with emphasis on the front leg hamstring muscle group, followed by a forward lunge position with emphasis on the rear leg quadriceps muscle group. In each position, four sets of stretches were completed each of 10 s duration with 5 s of rest between sets. The experimental group performed stretches with the vibration device turned on while the control group performed the same stretches with the vibration device turned off. A pre-test was performed to obtain baseline scores with the post-test following immediately after the vibration or control stretching intervention. Difference scores were calculated between the pre-test and post-test for each gymnast, and compared between groups using independent t-tests. Results showed significant post-test differences between the vibration and non-vibration groups (mean difference 12.2±5.2° vibration vs. 7.8±3.5° non-vibration, P=0.030) in the non-dominant limb, but no significant differences in the dominant limb (mean difference 10.2±4.3° vibration vs. 7.9±6.1° non-vibration, P=0.32). Vibration-assisted static stretching may provide a greater stimulus for range of motion improvements in limbs that have a lower initial level of flexibility.     

Kinematic analysis of the backstroke start: differences between backstroke specialists and non-specialists

Abstract

The purpose of this study was to clarify factors to perform the hole-entry technique in the backstroke start. A total of 16 well-trained Japanese competitive swimmers were divided into two groups (backstroke specialists and non-specialists) to compare their backstroke start motions. Their backstroke motions were videotaped, and two-dimensional co-ordinates for the swimmers were obtained from the video images using direct linear transformation methods. A non-paired t-test and Mann–Whitney U-test were used to analyse the statistical difference of the kinematic variables between the groups. Backstroke specialists showed a significantly shorter 5 m time (P = 0.009, effect size = –1.54), a significantly higher position of the toe (P = 0.010, effect size = 1.47) at signal and of the hip at toe-off (P = 0.002, effect size = 1.94), a significantly larger hip joint angle at toe-off (P = 0.007, effect size = 1.60) and a significantly higher angular velocities of the hip joints (45–85%; P < 0.05) for the normalised time as compared to that of non-specialists. An earlier initiation of the extension and the maintenance of a higher extension speed at the hip joints were important factors in achieving an arched-back posture, which facilitated and water entrance with a small entry range.     

Statistical modelling of knee valgus during a continuous jump test

Landing with the knee in a valgus position is recognized as a risk factor for anterior cruciate ligament (ACL) injury. Using linear and non-linear regression analyses, the purpose of this study was to examine the correlation between two-dimensional (2D) knee valgus and three-dimensional (3D) knee kinematics measured during a jump landing task. Twenty-eight female collegiate athletes participated. All participants were required to perform a continuous jump test. The average maximum angles of abduction and internal tibial rotation during landing were measured using the Point Cluster Technique. Average peak knee valgus angle was measured using a 2D approach. Linear and non-linear regression analyses between 2D valgus and 3D knee abduction, and between 2D valgus and 3D internal tibial rotation, were performed. The R ² value between 2D valgus and 3D knee abduction was significantly different from zero and had a moderate correlation for all models, whereas the R ² value between 2D valgus and 3D internal tibial rotation was not significantly different from zero. The 2D approach could be used to screen a specific group of individuals for risk of ACL injury; however, using frontal plane 2D analysis of valgus motion to evaluate internal tibial rotation is not advised.     

Alterations in kinematics and muscle activation patterns with the addition of a kipping action during a pull-up activity

Recently, addition of a gymnastics glide kip to a standard pull-up (SPU) has resulted in the kipping pull-up (KPU). Changes in muscle activation and kinematics were evaluated with eleven athletes performing sets of 5 SPU and 5 KPU. Surface electromyography of upper body and lower body muscles was recorded along with movement kinematics obtained via markers and motion tracking software. Most kinematic variables were significantly higher in the KPU including (KPU minus SPU deg): Max hip angle (48.8° ± 6.8°, p < 0.001) and max knee angle (56.5° ± 11.3°, p < 0.001). The recruitment of core and lower body muscles was significantly higher in the KPU (% MVIC increase): rectus abdominis (28.7 ± 4.7%, p < 0.001), external oblique (21.8 ± 4.1%, p < 0.001), iliopsoas (26.1 ± 5.5%, p = 0.001) and tensor fasciae latae (13.5 ± 2.3%, p < 0.001). Correspondingly, the biceps brachii had lower activation in the KPU (% MVIC decrease): (26.7 ± 0.6%, p = 0.006). Depending on the athlete’s goal, they may elect to perform an SPU for higher upper body muscle activation; or the KPU for more full-body activation with the potential to perform more repetitions through reduced upper body fatigue.     

四轮移动机器人运动控制系统设计

介绍了一种可在未知环境下自主工作的移动机器人运动控制系统设计。该控制系统采用TI公司TMS320LF2407DSP作为处理器,利用步进电机作为驱动装置。文章讨论了系统硬件设计、软件控制策略、速度控制器设计及其DSP实现。     

运动电荷作用在静止电荷上的力

文中利用洛仑兹变换给出了运动电荷作用在静止电荷上的力。     

SrRuO3是否为自旋玻璃

Ｔｈｉｓｗｏｒｋａｉｍｓａｔｃｒｅａｔｉｎｇａｍａｔｈｅｍａｔｉｃａｌｍｏｄｅｌａｂｌｅｔｏｄｅｓｃｒｉｂｅｔｈｅｍｏｔｉｏｎｏｆｐｕｒｅｒｏｌｌｉｎｇｏｆａｒｏａｄ ｖｅｈｉｃｌｅ ,ｗｈｅｎｔｈｅｅｌｅｃｔｒｉｃａｌｅｎｇｉｎｅｓａｃｔｄｉｒｅｃｔｌｙｏｎｔｈｅｗｈｅｅｌｓ.Ｆｕｒｔｈｅｒｍｏｒｅ ,ｉｔｓｈｏｕｌｄｂｅａｂｌｅｔｏｄｅｔｅｒｍｉｎｅｔｈｅｆｏｒｃｅｓｇｅｎｅｒａｔｅｄｂｙｔｈｅｃｏｎ ｔａｃｔｏｆｔｈｅｗｈｅｅｌｓｗｉｔｈｔｈｅｇｒｏｕｎｄ .　　Ｔｈｅｍｅｃｈａｎｉｃａｌｍｏｄｅ…     

高校田径教学中增设定向运动的可行性研究

近几年我国学生的身体素质,尤其是耐力素质出现了下降趋势,出现中长跑教学中的枯燥无味、学生锻炼积极性不高等状况,如何提高中长跑教学效果和学生耐力素质及应变能力,是我们体育教改面临的问题,而在而田径教学中增设定向运动,可作为高校体育课程改革和创新的突破口·