视觉运动追踪及其在体育运动中的应用与启示

运动员的视觉运动追踪能力是众多运动项目获得优异比赛成绩的关键因素,也是近些年运动心理学研究的重要问题。运用文献综述法对国内外关于视觉运动追踪的基本理论、研究范式及其在体育运动中的应用进行剖析,总结以往研究所取得的成果和存在的不足,探讨视觉运动追踪研究对体育运动成绩的影响与启示,为后续相关研究提供一定的思路与方法借鉴,为运动员心理选材及心理技能训练方法与策略提供理论参考和实证依据。     

Kinematic comparison of the seoi-nage judo technique between elite and college athletes

This study sought to identify biomechanical factors that determine fast and skilful execution of the seoi-nage (shoulder throw) technique by comparing kinematics between elite and college judo athletes. Three-dimensional motion data were captured using a VICON-MX system with 18 cameras operating at 250 Hz as three male elite and seven male college judo athletes performed seoi-nage. No significant difference was found in motion phase time of the turning phase between the two groups, indicating that motion phase time is not necessarily a factor contributing quickness in seoi-nage. The maximum relative velocity of the whole body centre of mass along the anterior–posterior direction was significantly greater in the elite athletes (2.74 ± 0.33 m/s) than in the college athletes (1.62 ± 0.47 m/s) during the turning phase (p = 0.023). The overall angular velocity of the body part lines, particularly the arm line, tended to be greater in the elite athletes (p = 0.068). The results imply that the velocity of the thrower relative to the opponent in the forward drive and turning motion reflects high skill seoi-nage. Coaches should recognise the relative forward velocity as a factor that may contribute to a successful seoi-nage when teaching the judo throw technique.     

Match-derived relative pitch area changes the physical and team tactical performance of elite soccer players in small-sided soccer games

Small-sided games (SSGs) are used in training sessions to prepare for full-sized matches. For the same number of players, smaller pitch sizes result in decreased physical performance and shorter interpersonal distances. A relative pitch area derived from the full-sized match results in larger pitch sizes and this may increase the fit between SSGs and full-sized matches. This study aimed to investigate SSGs with a traditional small pitch and a match-derived relative pitch area in youth elite soccer players. Four age categories (under-13, under-15, under-17 and under-19) played 4 vs. 4 plus goalkeepers on a small (40x30m, 120m² relative pitch area) and large pitch (68x47m, 320m² relative pitch area). The number of games per age category ranged 15–30. Positional data (LPM-system) were collected to determine physical (total distance covered, high intensity distance and number of sprints) and team tactical (inter-team distance, LPW-ratio, surface area, stretch indices, goalkeeper-defender distance) performance measures and tactical variability. On a large pitch, physical performance significantly increased, inter-team and intra-team distances were significantly larger and tactical variability of intra-team distance measures significantly increased. The match-derived relative pitch area is an important training manipulation and leads to changes in physical and tactical performance 4 vs. 4 plus goalkeepers.     

Kinematic analysis of proximal-to-distal and simultaneous motion sequencing of straight punches

Consecutive proximal-to-distal sequencing of motion is considered to be integral for generating high velocity of distal segments in many sports. Simultaneous usage of proximal and distal segments as seen in martial arts is by far less well investigated. Therefore, the aim of the study was to characterise and differentiate the concepts of consecutive (CSM) and simultaneous (SSM) sequence of motion in straight reverse punches as practised in Practical Wing Chun. Four experienced martial artists succeeded an eligibility test for technical proficiency in both concepts and performed a total number of 20 straight punches per concept. Eight MX13 Vicon cameras (250 fps) and Visual3D were used for motion capture and analyses. Both motion concepts showed proximal-to-distal sequencing of maximal joint velocities but, in SSM, this was coupled with simultaneous initiation. Key characteristics were: high pelvis momentum and backswing of shoulder and elbow (CSM); and importance of shoulder involvement (SSM). Different ranges of motion, timing aspects and achieved maximal angular velocities distinguished both concepts, which led to differences (p < 0.05) in fist velocity at contact, execution time, distance and horizontal shift of the centre of mass. Proper application of both concepts depends on the environmental setting, situational requirements and individual fighting style.     

Differences between motion capture and video analysis systems in calculating knee angles in elite-standard race walking

Race walking is an event where the knee must be straightened from first contact with the ground until midstance. The aim of this study was to compare knee angle measurements between 2D videography and 3D optoelectronic systems. Passive retroreflective markers were placed on the right leg of 12 race walkers and 3D marker coordinate data captured (250 Hz), with 2D video data (100 Hz) recorded simultaneously. Knee angle data were first derived based on the markers’ coordinates, and separately by using a 3D model that also incorporated thigh and shank clusters; the video data were analysed using both automatic tracking and manual digitising, creating four conditions overall. Differences were calculated between conditions for stance (using root mean square values), and at discrete events. There were few differences between systems, although the 3D model produced larger angles at midstance than using automatic tracking and marker coordinates (by 3 – 6°, P < 0.05). These differences might have occurred because of how the 3D model locates the hip joint, and because of the addition of marker clusters. 2D videography gave similar results to the 3D model when using manual digitising, as it allowed for errors caused by skin movement to be corrected.     

卫星和飞船跟踪测控的数学模型

卫星和飞船在国民经济和国防建设中有着重要作用,对卫星和飞船的测控成了航天系统的一个重要组成部分．在对卫星和飞船全程测控的前提下,分析了卫星和飞船在地球表面的星下点轨迹,并建立了简化的测控站分布模型．     

Use of probabilistic and deterministic measures to identify unfavorable earthquake records

This study introduces measures to identify resonant （concentration of energy in a single or a few frequencies） or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function （PSDF） of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records.     

The differential effects of PNF versus passive stretch conditioning on neuromuscular performance

Abstract

The effects of flexibility conditioning on neuromuscular and sensorimotor performance were assessed near to full knee extension (25°). Eighteen males who were randomly assigned into two groups underwent eight weeks (three-times per week) of flexibility conditioning (hip region/knee flexor musculature; dominant limb) involving either proprioceptive neuromuscular facilitation (PNF) (n=9) or passive stretching (PASS) (n=9). Both modes of flexibility conditioning are popular within contemporary exercise and clinical settings and have demonstrated efficacy in improving range of motion. The contralateral limb and a prior ‘no exercise’ condition were used as controls. The PNF and PASS modes of conditioning improved passive hip flexibility to a similar extent (mean 19.3% vs. baseline, intervention limb, p<0.01) but did not alter knee flexor strength (overall mean 309.6±81 N) or sensorimotor performance (force and positional errors: 2.3±8.2% and 0.48±7.1%). Voluntary and magnetically evoked electromechanical delays (EMD_V and EMD_E, respectively) were increased but to a greater extent following PASS compared to PNF (PASS: 10.8% and 16.9% lengthening of EMD_V and EMD_E, respectively vs. PNF: 3.2% and 6.2%, p<0.01).The attenuated change to electromechanical delay (EMD) performance during PNF conditioning suggests a preserved capability for rapid muscle activation, which is important in the maintenance of dynamic joint stability. That PNF was also equally efficacious in flexibility conditioning would suggest that this mode of flexibility training should be used over passive to help preserve dynamic joint stability capabilities at this extended and vulnerable joint position.     

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.