Effects of golf shaft stiffness on strain, clubhead presentation and wrist kinematics

The aim of this study was to quantify and explain the effect of shaft stiffness on the dynamics of golf drives. Twenty golfers performed swings with two clubs designed to differ only in shaft bending stiffness. Wrist kinematics and clubhead presentation to the ball were determined using optical motion capture systems in conjunction with a radar device for capturing ball speed, launch angle, and spin. Shaft stiffness had a marginally small effect on clubhead and ball speeds, which increased by 0.45% (p < 0.001) and 0.7% (p = 0.008), respectively, for the less stiff club. Two factors directly contributed to these increases: (i) a faster recovery of the lower flex shaft from lag to lead bending just before impact (p < 0.001); and (ii) an increase of 0.4% in angular velocity of the grip of the lower flex club at impact (p = 0.003). Unsurprisingly, decreases in shaft stiffness led to more shaft bending at the transition from backswing to downswing (p < 0.001). Contrary to previous research, lead bending at impact marginally increased for the stiffer shaft (p = 0.003). Overall, and taking effect sizes into account, the changes in shaft stiffness in isolation did not have a meaningful effect on the measured parameters, for the type of shaft investigated.     

摄像技术对提高U型场地单板雪上技巧训练效果的探讨

随着我国单板滑雪运动的不断发展,从事U型场地单板雪上技巧(以下简称单板雪上技巧)运动项目研究的每一位工作人员都在潜心研究提高运动成绩的有效的训练方法及其辅助手段,摄像技术是一种不可缺少的辅助手段。     

中国首届单板滑雪冠军赛调研

通过对我国首届单板滑雪冠军单赛调研,分析了黑龙江、吉林和辽宁三省参赛队伍的建制、选手年龄结构、目前运动技术水平等因素.对发展单板滑雪运动提出了建议.     

认识单板U型场地滑雪空中动作特征合理编排比赛动作

单板U型场地滑雪项目要求教练员、裁判员在吃准吃透评分标准的同时,还必须熟记动作名称及动作特征,只有这样,才能使教练员进行合理的动作编排,才有可能使裁判员快速、准确地进行客观的评分。依据国际雪联（FIS）单板滑雪裁判手册及竞赛规则,分析抓板技术特征、起飞技术特点,使教练员、裁判员认识与掌握单板U型场地滑雪项目空中动作的特征,提高动作编排技巧（得分）,进行更有效的基础训练;使目前我国这一项目的评分裁判员更清楚每一个技术动作的特点及难易度,进而更公正、准确地给运动员的表现进行评分。     

Effect of ice hockey stick stiffness on performance

Hockey sticks have undergone a dramatic transformation from wood to aluminum to composite in just over the past 20 years. With the introduction of different materials, there has been increasing interest in how the material properties affect shot speed. This study examined the effects of stick stiffness from measured swing motion on puck speed. Stick evaluation involved a six amateur player study, quasi-static stiffness measurement, video motion analysis, and numerical simulation. The effect of stiffness on puck speed was observed to depend on shot type. For shots involving large stick loading, as occurs with a slap shot, puck speed decreased as stick stiffness increased. The trend was consistent with a constant force player model. For shots involving low stick loading, as occurs with a wrist shot, puck speed increased as stick stiffness increased. The trend was consistent with a constant displacement player model. Finite element simulation of the slap shot agreed generally with the results of the player study and was used to find an optimal loading distance (distance that the stick contacts the ice prior to the puck) to be 24 cm.     

U型场地单板雪上技巧竞赛规则的变化引发的思考

通过研究分析U型场地单板雪上技巧竞赛规则的最新变化,旨在提高该项目的运动技术和裁判水平,鼓励运动员在比赛中大胆使用难新动作,增强整体效果.并提出了发展该项目的合理化建议.     

The influence of shaft stiffness on potential energy and puck speed during wrist and slap shots in ice hockey

The purpose of this study was to explore the relationship between hockey stick shaft stiffness and puck speed with mechanical energy considerations during stationary wrist and slap shots. Thirty left-handed pro-model composite hockey sticks, submitted by eleven hockey stick manufacturers, were subjected to a mechanical cantilever bend test to determine the shaft stiffness of each stick. Eight sticks representing the entire spectrum of stiffnesses were then used by five elite male hockey players to perform stationary wrist and slap shots in a laboratory setting. Eight infra-red high-speed digital video cameras were used to capture shaft deformation and puck speed. A second mechanical test then replicated the loading patterns applied to each stick during shooting. Force-deformation data from this test were used to determine the shaft stiffness and potential energy storage and return associated with each stick during shooting. The results of this study suggest that shaft stiffness has an influence on puck speed in wrist but not slap shots. During a wrist shot, a given player should realise higher puck speeds with a stick in which they store increased elastic potential energy in the shaft. In general, flexible sticks were found to store the most energy. However, how the athlete loads the stick has as much influence on puck speed as stick construction. Energy considerations were unable to explain changes in puck speed for the slap shot. For this type of shot it is the athlete and not the equipment influencing puck speed, but the governing mechanisms have yet to be elucidated.     

Converting between estimates of moderate-to-vigorous physical activity derived from raw accelerations measured at the wrist and from ActiGraph counts measured at the hip: the Rosetta Stone

The ability to compare published group-level estimates of objectively measured moderate-to-vigorous physical activity (MVPA) across studies continues to increase in difficulty. The objective of this study was to develop conversion equations and demonstrate their utility to compare estimates of MVPA derived from the wrist and hip. Three studies of youth (N = 232, 9-12yrs, 50% boys) concurrently wore a hip-worn ActiGraph and a wrist-worn GENEActiv for 7-days. ActiGraph hip count data were reduced using four established cutpoints. Wrist accelerations were reduced using the Hildebrand MVPA 200 mg threshold. Conversion equations were developed on a randomly selected subsample of 132 youth. Equations were cross-validated and absolute error, absolute percent error, and modified Bland-Altman plots were evaluated for conversion accuracy. Across equations R²_adj was 0.51–0.56 with individual-level absolute error in minutes ranging from 7 (wrist-to-hip Puyau) to 14.5 minutes (wrist-to-hip Freedson 3MET) and absolute percent differences ranging from 13.9%-24.5%. Group-level cross-validation to convert hip-to-wrist MVPA resulted in average absolute percent errors ranging from 3.1%-4.9%. Conversion of wrist-to-hip MVPA resulted in average absolute percent errors ranging from 3.0%-10.0%. We recommend the use of these equations to compare published estimates of MVPA between the wear-site cut-point combinations presented.     

Effect of sex and fatigue on muscle stiffness and musculoarticular stiffness of the knee joint in a young active population

The purpose of this study was to investigate the influence of sex and fatigue on knee extensor peak torque (PT), muscle stiffness (MS) of the vastus lateralis (VL) and knee joint musculoarticular stiffness (MAS) in young adults. Twenty-two male and 22 female recreational athletes participated. Males were characterised by higher relaxed [pre-: males 364.43 (52.00) N · m^–1, females 270.27 (37.25) N · m^–1; post-: males 446.75 (83.27) N · m^–1, females 307.39 (38.58) N · m^–1] and contracted [pre-: males 495.07 (71.04) N · m^–1, females 332.34 (85.42) N · m^–1; post-: males 546.37 (90.74) N · m^–1, females 349.21 (85.55) N · m^–1] MS of the VL, and knee joint MAS [pre-: males 1450.11 (507.98) N · m^–1, females 1027.99 (227.33) N · m^–1; post-: males 1345.81 (404.90) N · m^–1, females 952.78 (192.38) N · m^–1] than females pre- and post-fatigue. A similar finding was observed in pre-fatigue normalised knee extensor PT [pre-: males 2.77 (0.42) N · m kg^–1, females 2.41 (0.40) N · m kg^–1, post-: males 2.53 (0.54) N · m kg^–1, females 2.26 (0.44) N · m kg^–1]. After the fatigue protocol, normalised knee extensor PT and knee joint MAS decreased, whilst relaxed and contracted MS of the VL increased in both sexes. These observed differences may contribute to the higher risk of knee injury in females and following the onset of fatigue.     

从我国首届单板滑雪比赛分析此项目的现状及前景

运用现场观察法、访谈法、数据统计法等科学研究方法,对我国首届单板滑雪项目的特点及发展前景进行了评价和预测,并为今后的发展提出了建议.     

我国开展U型场地单板雪上技巧滑雪3年来的变化对比分析

就我国从2003年开展U型场地单板雪上技巧滑雪到现在3年的时间所发生的变化进行对比分析,了解发展势态,发现存在问题,提出加大“北雪南移”力度、重视科研攻关和广泛宣传对策。     

Characterizing the mechanical parameters of forward and backward falls as experienced in snowboarding

Wrist injuries are frequently observed after falls in snowboarding. In this study, laboratory experiments mimicking forward and backward falls were analysed. In six different falling scenarios, participants self-initiated falls from a static initial position. Eighteen volunteers conducted a total of 741 trials. Measurements were taken for basic parameters describing the kinematics as well as the biomechanical loading during impact, such as impact force, impact acceleration, and velocity. The effective mass affecting the wrist in a fall also was determined. The elbow angle at impact showed a more extended arm in backward falls compared to forward falls, whereas the wrist angle at impact remained similar in forward and backward falls. The study results suggest a new performance standard for wrist guards, indicating the following parameters to characterize an impact: an effective mass acting on one wrist of 3-5 kg, an impact angle of 75 degrees of the forearm relative to the ground, and an impact velocity of 3 m/s.     

Characterizing the mechanical parameters of forward and backward falls as experienced in snowboarding

Wrist injuries are frequently observed after falls in snowboarding. In this study, laboratory experiments mimicking forward and backward falls were analysed. In six different falling scenarios, participants self-initiated falls from a static initial position. Eighteen volunteers conducted a total of 741 trials. Measurements were taken for basic parameters describing the kinematics as well as the biomechanical loading during impact, such as impact force, impact acceleration, and velocity. The effective mass affecting the wrist in a fall also was determined. The elbow angle at impact showed a more extended arm in backward falls compared to forward falls, whereas the wrist angle at impact remained similar in forward and backward falls. The study results suggest a new performance standard for wrist guards, indicating the following parameters to characterize an impact: an effective mass acting on one wrist of 3–5 kg, an impact angle of 75° of the forearm relative to the ground, and an impact velocity of 3 m/s.     

Numerical study on the wrist action during the golf downswing

The purpose of this paper was to examine whether the ball position and wrist action (different types of torque application) could be optimised to increase the horizontal golf club head speed at impact with the ball. A two-dimensional double pendulum model of the golf downswing was used to determine to what extent the wrist action affected the club head speed in a driver, and how this affected the optimum ball position. Three different patterns of wrist actions (negative, positive, and negative-positive torque at the wrist) were investigated; and two criteria (maximum and impact criteria) were used to assess their effectiveness in terms of the maximum horizontal club head speed, and the club head speed as the shaft becomes vertical when viewed ‘face-on’. The simulation results indicated that the horizontal club head speed at impact could be increased by these patterns of wrist actions and the optimum ball position could be determined by the impact criterion. Based on the analysis of the energy flow from the input joints of shoulder and wrist to the arm and club head, the way the wrist action affects the club head speed has been discussed. The sensitivity of the results to small changes in model parameter values and initial conditions was investigated. The results were also examined under different torque patterns.     

800 m跑下肢垂直刚度与腿刚度的变化特征

利用弹簧质量模型对广东省第7届大学生运动会男子乙组800 m跑过程中,支撑腿垂直刚度及腿刚度进行探讨,结果表明:腿垂直刚度、腿刚度及跑速在100～200 m区间内达到峰值,并从此开始直到最后均呈连续下降;垂直刚度及腿刚度与跑速均存在显著的线性正相关,这种关联性也体现在与步频及步幅上;垂直刚度与支撑时间、腾空时间存在显著负相关,但却与腾空时间与支撑时间比值呈显著正相关,其深层原因有待于进一步探讨;800 m跑后期阶段,要想保持跑速,通过保持较高的垂直刚度来维持较高的步频最为关键.     

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.     

The influence of gender-related beliefs and conceptions of ability on women learning the hockey wrist shot

The purpose of this study was to determine the influence of beliefs about gender appropriateness and conceptions of ability on perceived and actual competene and patterns of behavior during practice of the hockey wrist shot. Sixty-eight undergraduate women formed four treatment conditions based on their beliefs about gender appropriateness and conceptions of ability. Four teachers taught across the treatment conditions for a total of 16 learning groups. Data were collected through a three-part questionnaire and from audio-video taping of the entire episode to ascertain the paticipants' competency beliefs, effort, and performance. Gender appropriateness impacted the participants' perceptions of competence and actual performance in the study, while beliefs about conceptions of ability did not produce a significant difference. This study reaffirms that educators must work diligently to combat the stereotypical beliefs many hold with respect to the gender appropriateness of physical activities.     

Understanding the role of shaft stiffness in the golf swing

Theoretically, shaft stiffness can alter shot distance by increasing clubhead speed or altering clubhead orientation at impact. A 3D forward dynamics model of a golfer and flexible club simulated the downswing. A genetic algorithm optimized the coordination of the model’s muscles (four torque generators) to maximize clubhead speed. The maximum torque output and maximum rate of torque development from the torque generators were varied to simulate the swing of golfers that generate different clubhead speeds. Four shafts of varying stiffness (flexible, regular, stiff, and completely rigid) were entered into these simulations to examine the role that shaft flexibility had on clubhead speed and orientation at impact. Shaft stiffness was found to have a meaningful effect only on clubhead orientation (dynamic loft and dynamic close) at impact. There was no evidence to support the premise that matching the stiffness properties of the shaft with the golfer would improve clubhead speed.