Ground reaction forces and osteogenic index of the sport of cyclocross

Abstract

Weight-bearing activity has been shown to increase bone mineral density. Our purpose was to measure vertical ground reaction forces (GRFs) during cyclocross-specific activities and compute their osteogenic index (OI). Twenty-five healthy cyclocross athletes participated. GRF was measured using pressure-sensitive insoles during seated and standing cycling and four cyclocross-specific activities: barrier flat, barrier uphill, uphill run-up, downhill run-up. Peak and mean GRF values, according to bodyweight, were determined for each activity. OI was computed using peak GRF and number of loading cycles. GRF and OI were compared across activities using repeated-measures ANOVA. Number of loading cycles per activity was 6(1) for barrier flat, 8(1) barrier uphill, 7(1) uphill run-up, 12(3) downhill run-up. All activities had significantly (P < 0.01) higher peak GRF, mean GRF values and OI when compared to both seated and standing cycling. The barrier flat condition (P < 0.01) had highest peak (2.9 times bodyweight) and mean GRF values (2.3 times bodyweight). Downhill run-up (P < 0.01) had the highest OI (6.5). GRF generated during the barrier flat activity is similar in magnitude to reported GRFs during running and hopping. Because cyclocross involves weight bearing components, it may be more beneficial to bone health than seated road cycling.     

Ground reaction forces, kinematics, and muscle activations during the windmill softball pitch

The aims of the present study were to examine quantitatively ground reaction forces, kinematics, and muscle activations during the windmill softball pitch, and to determine relationships between knee valgus and muscle activations, ball velocity and muscle activation as well as ball velocity and ground reaction forces. It was hypothesized that there would be an inverse relationship between degree of knee valgus and muscle activation, a direct relationship between ground reaction forces and ball velocity, and non-stride leg muscle activations and ball velocity. Ten female windmill softball pitchers (age 17.6 ± 3.47 years, stature 1.67 ± 0.07 m, weight 67.4 ± 12.2 kg) participated. Dependent variables were ball velocity, surface electromyographic (sEMG), kinematic, and kinetic data while the participant was the independent variable. Stride foot contact reported peak vertical forces of 179% body weight. There were positive relationships between ball velocity and ground reaction force (r = 0.758, n = 10, P = 0.029) as well as ball velocity and non-stride leg gluteus maximus (r = 0.851, n = 10, P = 0.007) and medius (r = 0.760, n = 10, P = 0.029) muscle activity, while there was no notable relationship between knee valgus and muscle activation. As the windmill softball pitcher increased ball velocity, her vertical ground reaction forces also increased. Proper conditioning of the lumbopelvic-hip complex, including the gluteals, is essential for injury prevention. From the data presented, it is evident that bilateral strength and conditioning of the gluteal muscle group is salient in the windmill softball pitch as an attempt to decrease incidence of injury.     

The effects of opposition and gender on knee kinematics and ground reaction force during landing from volleyball block jumps

The aim of this study was to examine the effect of opposition and gender on knee kinematics and ground reaction force during landing from a volleyball block jump. Six female and six male university volleyball players performed two landing tasks: (a) an unopposed and (b) an opposed volleyball block jump and landing. A 12-camera motion analysis system (120 Hz) was used to record knee kinematics, and a force platform (600 Hz) was used to record ground reaction force during landing. The results showed a significant effect for level of opposition in peak normalized ground reaction force (p = .04), knee flexion at ground contact (p = .003), maximum knee flexion (p = .001), and knee flexion range of motion (p = .003). There was a significant effect for gender in maximum knee flexion (p = .01), knee flexion range of motion (p = .001), maximum knee valgus angle (p = .001), and knee valgus range of motion (p = .001). The changes in landing biomechanics as a result of opposition suggest future research on landing mechanics should examine opposed exercises, because opposition may significantly alter neuromuscular responses.     

Ground reaction forces and kinematics of plant leg position during instep kicking in male and female collegiate soccer players

The players' ability to achieve the greatest distance in kicking is determined by their efficiency in transferring kinetic energy from the body to the ball. The purpose of this study was to compare the kinetics and kinematics of the plant leg position between male and female collegiate soccer players during instep kicking. Twenty-three soccer players (11 males and 12 females) were filmed in both the sagittal and posterior views while performing a maximal instep kick. Plant leg kinetic data were also collected using an AMTI 1000 force platform. There were no significant differences between the sexes in plant leg position, but females had significantly greater trunk lean, plant leg angle, and medial-lateral ground reaction force than the males. Males showed higher vertical ground reaction forces at ball contact, but there were no significant differences in ball speed at take-off between the sexes. Ball speed at take-off was inversely related to peak anterior-posterior ground reaction force (-0.65). The anatomical differences between the sexes were reflected in greater trunk lean and lower leg angle in the females.     

The effects of baseball bat mass properties on swing mechanics,ground reaction forces,and swing timing

Swing trajectory and ground reaction forces (GRF) of 30 collegiate baseball batters hitting a pitched ball were compared between a standard bat, a bat with extra weight about its barrel, and a bat with extra weight in its handle. It was hypothesised that when compared to a standard bat, only a handle-weighted bat would produce equivalent bat kinematics. It was also hypothesised that hitters would not produce equivalent GRFs for each weighted bat, but would maintain equivalent timing when compared to a standard bat. Data were collected utilising a 500 Hz motion capture system and 1,000 Hz force plate system. Data between bats were considered equivalent when the 95% confidence interval of the difference was contained entirely within ±5% of the standard bat mean value. The handle-weighted bat had equivalent kinematics, whereas the barrel-weighted bat did not. Both weighted bats had equivalent peak GRF variables. Neither weighted bat maintained equivalence in the timing of bat kinematics and some peak GRFs. The ability to maintain swing kinematics with a handle-weighted bat may have implications for swing training and warm-up. However, altered timings of kinematics and kinetics require further research to understand the implications on returning to a conventionally weighted bat.     

Effects of a combined inversion and plantarflexion surface on knee and hip kinematics during landing

Although landing in a plantarflexion and inversion position is a well-known characteristic of lateral ankle sprains, the associated kinematics of the knee and hip is largely unknown. Therefore, the purpose of this study was to examine the changes in knee and hip kinematics during landings on an altered landing surface of combined plantarflexion and inversion. Participants performed five drop landings from 30 cm onto a trapdoor platform in three different conditions: flat landing surface, 25° inversion, or a combined 25° plantarflexion and 25° inversion. Kinematic data were collected using a seven camera motion capture system. A 2 × 3 (leg × surface) repeated measures ANOVA was used for statistical analysis. The combined surface showed decreased knee and hip flexion range of motion (ROM) and increased knee abduction ROM (p < 0.05). The altered landing surface creates a stiff landing pattern where reductions in sagittal plane motion are transferred to the frontal plane, resulting in increased knee abduction. A stiff landing pattern is frequently related to increased risk of anterior cruciate ligament injury. It may be beneficial for athletes at risk to train for alternate methods of increasing their sagittal plane motion of the knee and hip with active knee or trunk flexion.     

我国优秀女子跳远运动员摆动腿在助跑与起跳阶段的运动学诊断

运用灵像解析的方法对8名中国女子跳远运动员（平均成绩6．29m）和10名美国运动员（平均成绩6．52m）有关运动学参数进行对比、诊断。研究表明，我国优秀女子跳远运动员摆动腿在助跑最后一步蹬伸阶段的伸髋平均水平速度和着板时摆动角速度两项指标上有一定的不足；在助跑最后一步中，摆动腿放脚速度慢，髋关节前送技术差，导致摆动腿支撑扇角较大，这是我国运动员在此阶段不能保持较高水平速度的直接原因；在助跑最后一步蹬伸阶段中，由于摆动腿离地时的膝角较大，“屈蹬”技术形成的不够理想，推迟了我国运动员摆动的时机；在着板时，我国运动员应主动积极地加快摆动腿的摆动，以此带动起跳脚脚掌向后的加速踏板动作，同时努力使着板角达到费尔歇模式；起跳过程的缓冲阶段是获得垂直速度的主要阶段，加快摆动腿的摆动速度是损失较小水平速度、获得较大垂直速度的有效途径。     

Comparison of 2D video and electrogoniometry measurements of knee flexion angle during a countermovement jump and landing task

Quantifying countermovement jump (CMJ) and landing knee flexion angle is important for performance and injury risk assessment. The purpose of the study was to compare electrogoniometer (El-Gon)- and video-derived CMJ and landing knee flexion angle. Twenty-two adults performed three CMJs while knee flexion angle was simultaneously assessed using an El-Gon and video. The average systematic offset (RMSE) of the El-Gon-derived knee flexion angle throughout the entire movement was 7.03°?±?2.69°. Excellent reliability was demonstrated by the El-Gon (ICCavg?=?0.92). Countermovement knee flexion angle, maximum landing knee flexion angle and flexion angle at maximum vertical ground reaction force were 12.0°, 10.9°, and 5.7° higher, respectively, when assessed using El-Gon (p?<?0.001), compared to video. Errors between instruments are likely due to El-Gon crosstalk, misalignment and/or axis determination. The El-Gon is a cost-effective and time-efficient alternative to video analysis for the assessment of knee flexion angle if the error is accounted for and the sensor is precisely attached.     

背越式跳高助跑最后一步和起跳阶段摆动腿技术的特征及其动能变化研究

通过三维摄影对我国优秀男子背越式跳高运动员在助跑最后一步和起跳阶段摆动腿的支撑与摆动技术的运动学特征进行分析,结果表明,助跑最后一步和起跳阶段摆动腿的支撑与摆动技术对身体重心的运动状况具有重要的影响.     

Changes in muscle-tendon length during the take-off of a running long jump

The aims of this study were to determine: (1) the modes of action of selected muscles of the supporting leg during the take-off of a running long jump; (2) whether the instant at which maximum knee flexion is recorded is a valid indicator of the instant these muscles change their modes of action; and (3) the relationships between the actions of these muscles and the change in the vertical velocity of the centre of mass during the take-off. Eleven elite, female long jumpers performed six jumps from a full-length approach. A model of selected muscles of the jumping leg was developed to estimate muscle-tendon lengths from segment positions obtained using cinematography. Only half of the muscles exhibited a lengthening-shortening sequence of activity. The instant at which maximum knee flexion was recorded was a poor indicator of when the muscles changed from eccentric to concentric activity. The more the vasti muscles were stretched, the larger the gain in vertical velocity; the longer the triceps surae muscles at touchdown, the more they were stretched, and the faster they were stretched, the larger the gain in vertical velocity. Enhancement through use of the stretch-shortening cycle did not make a significant contribution to vertical velocity via the actions of the vasti and triceps surae muscles.     

The effect of pitch type on ground reaction forces in the baseball swing

Coaches have identified the batter's weight shift as a critical component for promoting proper timing and balance in a baseball swing. Analysing the weight shift through maximum horizontal (Fx) and vertical (Fz) ground reaction forces (GRFs) of professional batters (N = 29; height = 185 +/- 6 cm; mass = 92 +/- 9 kg), the purpose of this study was to compare GRFs among swings against fastballs and changeups. General linear models were used to compare three conditions of interest: successful results against fastballs, successful results against changeups, and unsuccessful results against changeups. Batters had a similar loading mechanism and initial weight transfer from back foot to front foot regardless of pitch type, but peak front foot GRFx and GRFz occurred with significantly different magnitudes and at significantly different times, depending on the pitch type and hit result. Peak front foot GRFs were greater for successful swings against fastballs compared to both successful and unsuccessful swings against changeups. Peak front foot GRFs of unsuccessful swings against changeups occurred, on average, 15-20 ms earlier than successful swings against changeups and 30-35 ms earlier than successful swings against fastballs, quantifying how a changeup can disrupt the coordination of a hitter's weight shift.     

对个体速滑运动员髋、膝、踝三关节伸屈肌群力学性质的研究与分析

试验对象为2名国家健将级速滑运动员,用CYBEX NORM测髋、膝、踝三关节屈伸肌群的力矩.一组试验由8个角速度的试验组成.实验时,角速度间休息20s,组间休息半小时.每个人做3组试验.各人试验数据按关节角(间隔5°)、角速度组成样本后,做各关节角的不同速度的伸屈髋、膝、踝肌群的参数曲线族.试验发现:伸髋肌群在100°～145°之间时为较适宜发力区.而屈髋肌群在125°～165°之间为较适宜发力区.从最大力矩发生角度看,伸髋在115°～120°之间,屈髋在150°～155°之间.伸膝的适宜发力区在105°～145°之间,最大力矩值均发生在110°～120°之间.而屈膝适宜发力区在110°～155°之间,最大力矩值均发生在135°～145°之间.踝关节肌群无论是适宜发力区还是最大肌力的发生角度都随角速度的增加有所变化.     

体育舞蹈的发展及其在高校教学的开展教学

体育舞蹈是一项新兴的运动项目，本对它的产生和发展作了深入的探讨与研究，并对它作为一门体育课程进入大学体育教学课堂的意义作了阐述。还对体育舞蹈课的教学提出了一些构想。     

广东民间体育"英歌舞"的创编

英歌舞的创编应体现现代艺术与传统风格的结合,注重主题内涵的表达,大力发展舞台英歌舞等指导思想.英歌舞创编的方法可以从槌法、其他舞蹈表演、生产劳动和日常生活、武术搏击内容、事物的拟态、人物特征等方面去思考.     

手臂摆动在跳高起跳中的生物力学意义

用模型研究法对跳高起跳中的手臂摆动进行了研究．分析了起跳前手臂和身体其余部分的受力情况．探讨了起跳时加速力的产生过程,比较了手臂不同的加速摆动方式对身体重心最后速度的影响。由此指出,手臂摆动对身体起跳加速力的贡献率很大,并且,手臂加速摆动的距离越长,身体重心速度的增加越明显。     

Simultaneous measurement of back and front foot ground reaction forces during the same delivery stride of the fast-medium bowler

Six male cricket bowlers (mean - s x ¥ : age 23.5 - 1.3 years; height 1.83 - 0.04 m; body weight 826 - 20 N) performed their typical bowling action at a set of stumps positioned at standard pitch length (20.1 m). A specially designed force platform rig allowed the correct positioning of two force platforms to be achieved beneath an outdoor polyflex runway (0.017 m depth) for each player's delivery stride pattern. For the back foot, the peak vertical ground reaction force was 1.95 - 0.08 kN (2.37 - 0.14 BW) and the braking force was 0.77 - 0.12 kN (0.94 - 0.16 BW). For the front foot, the peak vertical force was 4.80 - 0.92 kN (5.75 - 0.98 BW) and the braking force was 2.93 - 0.56 kN (3.54 - 0.67 BW). The mean peak vertical loading rate for front foot contact was 205 - 52.8 kN·s -1 (249 - 64 BW·s -1 ) with mean values ranging from 81 to 446 kN·s -1 (98 to 540 BW·s-1). The range for back foot contact was much smaller, 25-70 kN·s -1 (30-85 BW·s -1 ), with a mean of 41.7 - 7.10 kN·s -1 (50.6 - 8.6 BW·s -1 ). Mean peak impact occurred 24 ms after touchdown for the back foot and 16 ms after touchdown for the front foot. At impact, mean peak loading rates were greater for the front foot at 246 kN·s -1 (298 BW·s -1 ), with a range of 80-483 kN·s -1 (98-534 BW·s -1 ), than for the back foot at 65 kN·s -1 (79 BW·s -1 ), with a range of 40-84 kN·s -1 (49-110 BW·s -1 ).     

Simultaneous measurement of back and front foot ground reaction forces during the same delivery stride of the fast-medium bowler

Six male cricket bowlers (mean +/- s(mean): age 23.5 +/- 1.3 years; height 1.83 +/- 0.04 m; body weight 826 +/- 20 N) performed their typical bowling action at a set of stumps positioned at standard pitch length (20.1 m). A specially designed force platform rig allowed the correct positioning of two force platforms to be achieved beneath an outdoor polyflex runway (0.017 m depth) for each player's delivery stride pattern. For the back foot, the peak vertical ground reaction force was 1.95 +/- 0.08 kN (2.37 +/- 0.14 BW) and the braking force was 0.77 +/- 0.12 kN (0.94 +/- 0.16 BW). For the front foot, the peak vertical force was 4.80 +/- 0.92 kN (5.75 +/- 0.98 BW) and the braking force was 2.93 +/- 0.56 kN (3.54 +/- 0.67 BW). The mean peak vertical loading rate for front foot contact was 205 +/- 52.8 kN x s(-1) (249 +/- 64 BW x s(-1)) with mean values ranging from 81 to 446 kN x s(-1) (98 to 540 BW x s(-1)). The range for back foot contact was much smaller, 25-70 kN x s(-1) (30-85 BW x s(-1)), with a mean of 41.7 +/- 7.10 kN x s(-1) (50.6 +/- 8.6 BW x s(-1)). Mean peak impact occurred 24 ms after touchdown for the back foot and 16 ms after touchdown for the front foot. At impact, mean peak loading rates were greater for the front foot at 246 kN x s(-1) (298 BW x s(-1)), with a range of 80-483 kN x s(-1) (98-534 BW x s(-1)), than for the back foot at 65 kN x s(-1) (79 BW x s(-1)), with a range of 40-84 kN x s(-1) (49-110 BW x s(-1)).     

体育舞蹈教学训练中的音乐节奏处理

从舞蹈技术理论角度出发就体育舞蹈教学、训练中存在的音乐节奏问题进行了论述，并对摩登舞华尔兹、探戈音乐节奏处理问题作了探讨。     

高校开设街舞课程可行性分析

街舞是西方现代社会文化的产物，舞者洒脱宽松的衣着，利落多变的动作，强烈的音乐节奏，营造出震撼的动感，充分展示了现代青少年无拘无束、勇于创新的精神特质。将街舞列入高校体育教学课程有其现实意义。