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1.
跳绳运动是体能训练之一,但是不同跳绳运动频率在运动训练的效益与人体健康的影响仍有待探讨。利用VICON动作捕捉系统及Kistler测力板撷取受过跳绳运动训练的15位小学生选手的下肢运动学资料及地面反作用力值,并采用重复量数单因子变异数分析检定三种频率跳绳运动各组间的跳跃高度及运动学参数是否有差异,统一显著水平定为α=．05,达显著时再用杜凯氏HSD法做事后比较。在探讨在跳绳运动训练过程中,进行低频组（60±2次／分钟）、中频组（100±2次／分钟）及高频组（140±2次／分钟）跳绳运动,下肢所受到相关力学参数的差异,以及下肢关节运动学变化及下肢劲度对着地策略的影响情形。研究结果表明,不同频率跳绳运动的垂直地面反作用力的最大值、被动冲量、负荷率、下肢劲度及角劲度值以高频组较高;不同频率跳绳运动的动作时间以低频组较多;下肢各关节角度变化量方面膝关节角度变化在中频组有突增现象（p〈05）。建议进行跳绳运动运动时,仍应注意高频率跳跃时垂直地面反作用力对人体的冲击。  相似文献   

2.
In this study, we examined the relative control of reaction time and force in responses of the lower limb. Fourteen female participants (age 21.2 +/- 1.0 years, height 1.62 +/- 0.05 m, body mass 54.1 +/- 6.1 kg; mean +/- s) were instructed to exert their maximal isometric one-leg extension force as quickly as possible in response to an auditory stimulus presented after one of 13 foreperiod durations, ranging from 0.5 to 10.0 s. In the 'irregular condition' each foreperiod was presented in random order, while in the 'regular condition' each foreperiod was repeated consecutively. A significant interactive effect of foreperiod duration and regularity on reaction time was observed (P < 0.001 in two-way ANOVA with repeated measures). In the irregular condition the shorter foreperiod induced a longer reaction time, while in the regular condition the shorter foreperiod induced a shorter reaction time. Peak amplitude of isometric force was affected only by the regularity of foreperiod and there was a significant variation of changes in peak force across participants; nine participants were shown to significantly increase peak force for the regular condition (P < 0.001), three to decrease it (P < 0.05) and two showed no difference. These results indicate the independence of reaction time and response force control in the lower limb motor system. Variation of changes in peak force across participants may be due to the different attention to the bipolar nature of the task requirements such as maximal force and maximal speed.  相似文献   

3.
Whilst the measurement and quantification of vertical leg stiffness (Kvert) asymmetry is of important practical relevance to athletic performance, literature investigating bilateral asymmetry in Kvert is limited. Moreover, how the type of task used to assess Kvert may affect the expression of asymmetry has not been properly determined. Twelve healthy males performed three types of performance tasks on a dual force plate system to determine Kvert asymmetries; the tasks were (a) bilateral hopping, (b) bilateral drop jumping and (c) unilateral drop jumping. Across all the three methods, Kvert was significantly different between compliant and stiff limbs (P < 0.001) with a significant interaction effect between limb and method (P = 0.005). Differences in Kvert between compliant and stiff limbs were ?5.3% (P < 0.001), ?21.8% (P = 0.007) and ?15.1% (P < 0.001) for the bilateral hopping, bilateral drop jumping and unilateral drop jumping methods, respectively. All the three methods were able to detect significant differences between compliant and stiff limbs, and could be used as a diagnostic tool to assess Kvert asymmetry. Drop jumping tasks detected larger Kvert asymmetries than hopping, suggesting that asymmetries may be expressed to a greater extent in acyclic, maximal performance tasks.  相似文献   

4.
The aim of this study was to evaluate the reliability of two long jump tasks and their ability to predict 10 m sprint performance in elite adolescent female athletes. Eight junior national-level female track and field athletes completed three standing (SLJ) and reactive long jumps (RLJ) on portable force plates, followed by three 10 m sprints. Intra-class correlation coefficients (ICC) and coefficients of variation (CV) were calculated to examine reliability. Linear regression results identified the best predictor of average and best 10 m sprint time from the jump kinematic and kinetic measures. The ICCs and CVs indicated good reliability for the majority of kinetic measures however, better reliability was reported for the SLJ. The SLJ was a good predictor of best and average 10 m sprint time, with average horizontal power the best predictor of performance (best; R 2 = 0.751, p = 0.003, Standard Error of Estimate (SEE)% = 2.2 average; R 2 = 0.708, p = 0.005, SEE% = 2.5).  相似文献   

5.
In this study, we examined the relative control of reaction time and force in responses of the lower limb. Fourteen female participants (age 21.2±1.0 years, height 1.62±0.05?m, body mass 54.1±6.1?kg; mean±s) were instructed to exert their maximal isometric one-leg extension force as quickly as possible in response to an auditory stimulus presented after one of 13 foreperiod durations, ranging from 0.5 to 10.0?s. In the ‘irregular condition’ each foreperiod was presented in random order, while in the ‘regular condition’ each foreperiod was repeated consecutively. A significant interactive effect of foreperiod duration and regularity on reaction time was observed (P?<?0.001 in two-way ANOVA with repeated measures). In the irregular condition the shorter foreperiod induced a longer reaction time, while in the regular condition the shorter foreperiod induced a shorter reaction time. Peak amplitude of isometric force was affected only by the regularity of foreperiod and there was a significant variation of changes in peak force across participants; nine participants were shown to significantly increase peak force for the regular condition (P?<?0.001), three to decrease it (P?<?0.05) and two showed no difference. These results indicate the independence of reaction time and response force control in the lower limb motor system. Variation of changes in peak force across participants may be due to the different attention to the bipolar nature of the task requirements such as maximal force and maximal speed.  相似文献   

6.
The aim of this study was to evaluate the reliability of two long jump tasks and their ability to predict 10 m sprint performance in elite adolescent female athletes. Eight junior national-level female track and field athletes completed three standing (SLJ) and reactive long jumps (RLJ) on portable force plates, followed by three 10 m sprints. Intra-class correlation coefficients (ICC) and coefficients of variation (CV) were calculated to examine reliability. Linear regression results identified the best predictor of average and best 10 m sprint time from the jump kinematic and kinetic measures. The ICCs and CVs indicated good reliability for the majority of kinetic measures however, better reliability was reported for the SLJ. The SLJ was a good predictor of best and average 10 m sprint time, with average horizontal power the best predictor of performance (best; R2 = 0.751, p = 0.003, Standard Error of Estimate (SEE)% = 2.2 average; R2 = 0.708, p = 0.005, SEE% = 2.5).  相似文献   

7.
The purpose of this study was the experimental validation of the OpenGo sensor insole system compared to PedarX sensor insole and AMTI force-plate systems. Sixteen healthy participants performed trials in walking, running, jumping (drop and counter movement jumps), imitation drills and balance, with simultaneous measures of all three systems. Detected ground contact and flight times with OpenGo during walking, running and jumping were similar to those of AMTI. Force–time curves revealed comparable shapes between all three systems. Force impulses were 13–34% lower with OpenGo when compared to AMTI. Despite differences in mean values in some exercise modes, correlations towards AMTI were between r = 0.8 and r = 1.0 in most situations. During fast motions, with high force and impact, OpenGo provided lower force and latency in force kinetics. During balance tasks, discrepancy in the centre of pressure was found medio-lateral, while anterio–posterior direction was closer to AMTI. With awareness of these limitations, OpenGo can be applied in both clinical and research settings to evaluate temporal, force and balance parameters during different types of motion. The fully mobile OpenGo system allows for the easy and quick system application, analysis and feedback under complex field conditions, as well.  相似文献   

8.
This study investigated whether neuromuscular fatigue affects the neuromuscular control of an athlete within a sports context setting and whether these effects were more pronounced in the females. Lower limb joint kinetics of 6 male and 6 female inter-varsity soccer players performing side-stepping tasks in non-fatigue versus fatigue and anticipated versus unanticipated conditions were quantified using 10 Motion Analysis Corporation cameras and a Kistler? force platform. The Yo-Yo intermittent recovery Level 1 fatigue protocol was employed. Stance foot initial contact and peak forces, and peak joint knee moments of the lower limb were submitted to a 3-way mixed-model repeated measure ANOVA. The results suggested that males tend to elicit significantly higher knee joint loadings when fatigued. In addition, males elicited significantly higher peak proximal tibia anterior/posterior shear force, vertical ground reaction force at initial contact and peak internal rotational moments than females. These findings suggested that males were at greater overall injury risk than females, especially in the sagittal plane. Neuromuscular control-based training programmes/interventions that are designed to reduce the risk of the non-contact ACL injury need to be customised for the different genders.  相似文献   

9.
Abstract

The aim of this study was to examine the effects of arm-swing and sporting activity on jump height and jump height variability of countermovement jumps in adolescent students to inform correct jumping technique in different settings. Altogether, 324 students (grades 5–11) performed three countermovement jumps with bilateral arm-swings and three countermovement jumps without arm-swings on a force platform. The participants were divided into three groups based on sporting activity. The groups with the most (“active group”; more than 6 h formal athletics in a sport club per week) and least active (“sedentary group”; less than 3 h formal athletics in a sport club per week) participants were compared. Jump height was calculated for all jumps, and the best trial of three was used for further analysis. Jump height variability was indicated by the coefficient of variation over three jumps. The reliability of jump height was determined using the intra-class correlation coefficient (ICC) over three trials of each jumping technique. The reliability of jump height was very high for all conditions (ICC: 0.90–0.96). Jump height was significantly higher for countermovement jumps with than without arm-swings for both groups. Jump height in the active group was significantly greater than in the sedentary group for both jumping techniques. A significant interaction between jumping technique and sporting activity indicates a greater benefit of arm-swing in the active than in the sedentary participants. No significant differences between groups were observed for jump height variability. Jump height can be measured reliably in active and sedentary adolescent individuals for both jumping techniques. The relevant jumping technique should be chosen with respect to the context of its application and based on its suitability for the individual and task of interest.  相似文献   

10.
Overuse injuries, resulting from repetitive subacute impact loading, are a problem in high-performance sports. Monitoring of impact loading may aid in the prevention of these injuries. The current study aimed to establish the intra-day and inter-day reliability of a tri-axial accelerometer to assess impact loading during jumping and landing tasks. Twelve participants wore an accelerometer on their upper and lower back. They performed a continuous hopping task as well as drop landings and rebound jumps from three drop heights (37.5, 57.5 and 77.5 cm), peak resultant acceleration (PRA) was calculated for all tasks. The tasks were performed twice, one week apart at the same time of day. The difference in the mean, intra-class correlation coefficient, coefficient of variation and Cohen’s effect size were calculated as measures of reliability. PRA showed good intra-day reliability for the hopping task. Inter-day reliability of the PRA was moderate to good across all tasks. Reliability of PRA was slightly higher when accelerations were recorded on the lower back compared to the upper back. To assess impact loading, during continuous hopping, drop landings and rebound jumps, PRA recorded at both the upper and lower back appears to be a reliable measure.  相似文献   

11.
The aim of this study was to examine the biomechanical injury risk factors at the wrist, including joint kinetics, kinematics and stiffness in the first and second contact limb for parallel and T-shape round-off (RO) techniques. Seven international-level female gymnasts performed 10 trials of the RO to back handspring with parallel and T-shape hand positions. Synchronised kinematic (3D motion analysis system; 247 Hz) and kinetic (two force plates; 1235 Hz) data were collected for each trial. A two-way repeated measure analysis of variance (ANOVA) assessed differences in the kinematic and kinetic parameters between the techniques for each contact limb. The main findings highlighted that in both the RO techniques, the second contact limb wrist joint is exposed to higher mechanical loads than the first contact limb demonstrated by increased axial compression force and loading rate. In the parallel technique, the second contact limb wrist joint is exposed to higher axial compression load. Differences between wrist joint kinetics highlight that the T-shape technique may potentially lead to reducing these bio-physical loads and consequently protect the second contact limb wrist joint from overload and biological failure. Highlighting the biomechanical risk factors facilitates the process of technique selection making more objective and safe.  相似文献   

12.
Ballistic limb motion is enabled by proximal “core” stiffness. However, controversy exists regarding the best method of training this characteristic. This study sought to determine the most effective core training method to enhance distal limb athleticism. A total of 12 participants (24 ± 3 years, 1.8 ± 0.05 m, 76.8 ± 9.7 kg) consisting of Muay Thai athletes performed a core training protocol (Isometric vs. Dynamic, with Control) for 6 weeks, using a repeated measures design to assess performance (peak strike velocity, peak impact force, muscular activation) in various strikes. Isometric training increased impact force in Jab (554.4 ± 70.1 N), Cross (1895.2 ± 203.1 N), Combo (616.8 ± 54.9 N), and Knee (1240.0 ± 89.1 N) trials (P < 0.05). Dynamic training increased strike velocity in Jab (1.3 ± 0.2 m · s?1), Cross (5.5 ± 0.9 m · s?1), Combo (0.7 ± 0.1, 2.8 ± 0.3 m · s?1), and Knee (3.2 ± 0.3 m · s?1) trials (P < 0.05). Isometric training increased Combo impact force 935.1 ± 100.3 N greater than Dynamic and 931.6 ± 108.5 N more than Control (P < 0.05). Dynamic training increased Jab strike velocity 1.3 ± 0.1 m · s?1 greater than Isometric and 0.8 ± 0.1 m · s?1 more than Control (P < 0.05). It appears that both static and dynamic approaches to core training are needed to enhance both velocity and force in distal limbs.  相似文献   

13.
Abstract The 'stiffness' concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness measurement exists bringing into question the integrity of some research related to stiffness. The aim of this study was to review literature which describes how vertical, leg and knee stiffness has been measured in adult populations while running, jumping or hopping. A search of the entire MEDLINE, PubMed and SPORTDiscus databases and an iterative reference check was performed. Sixty-seven articles were retrieved; 21 measured vertical stiffness, 51 measured leg stiffness, and 22 measured knee stiffness. Thus, some studies measured several 'types' of stiffness. Vertical stiffness was typically the quotient of ground reaction force and centre of mass displacement. For leg stiffness it was and change in leg length, and for the knee it was the quotient of knee joint moments and change in joint angle. Sample size issues and measurement techniques were identified as limitations to current research.  相似文献   

14.
Abstract

The ‘stiffness’ concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness measurement exists bringing into question the integrity of some research related to stiffness. The aim of this study was to review literature which describes how vertical, leg and knee stiffness has been measured in adult populations while running, jumping or hopping. A search of the entire MEDLINE, PubMed and SPORTDiscus databases and an iterative reference check was performed. Sixty-seven articles were retrieved; 21 measured vertical stiffness, 51 measured leg stiffness, and 22 measured knee stiffness. Thus, some studies measured several ‘types’ of stiffness. Vertical stiffness was typically the quotient of ground reaction force and centre of mass displacement. For leg stiffness it was and change in leg length, and for the knee it was the quotient of knee joint moments and change in joint angle. Sample size issues and measurement techniques were identified as limitations to current research.  相似文献   

15.
This study investigated the relationship between several measures of lower-body stiffness and physical performance variables in 22 sub-elite male football players (mean ± SD; 21.9 ± 1.5 yr; 1.79 ± 0.06 m; 72.2 ± 7.2 kg). The participants were assessed for individual muscle stiffness of the Rectus Femoris (RF), Biceps Femoris (BF) and Medial Gastrocnemius (MG) muscles and vertical stiffness (Kvert) was also assessed assessed running acceleration, maximal sprint speed, agility, vertical jumping and muscular strength. Pearson’s correlations quantified the relationships and participants were also separated into relatively stiff (SG) and compliant groups (CG) for each variable. When ranked by Kvert the SG exhibited superior performance during sprinting, agility, jumping and strength (p ≤ 0.05) and when ranked by RF stiffness, SG exhibited superior sprint, agility and drop jump performance (p ≤ 0.05), while MG and BF stiffness were not related to performance. Higher stiffness appears to be beneficial to athletic performance for football players and therefore it may be beneficial for practitioners working with athletes that are required to perform dynamic activities to consider the contribution of stiffness to athletic performance.  相似文献   

16.
Track and field events place different demands on athletes and may have an effect on balance. This study investigated the effects of event specialty, gender, and leg dominance on balance among adolescent track and field athletes. Forty healthy adolescent track and field athletes (male = 23, female = 17) categorised into three different groups (sprinter = 20, distance runners = 13, throwers = 7) had their single leg static balance measured with the eyes open and the eyes closed using an AMTI force platform. Dependent variables included average displacement (cm) of the centre of pressure (COP) in the anterior/posterior direction and medial/lateral directions, the average velocity of the COP (cm/s) and the 95% ellipse area (cm2). Variables were analysed using a 3 (event specialty) × 2 (gender) × 2 (leg) ANOVA with repeated measures on the leg variable (p < 0.05). There was a significant difference (p < 0.05) in the average displacement of the COP in the medial/lateral direction for both the eyes open and closed condition, with the non-dominant leg demonstrating greater displacement than the dominant leg. This might increase the risk of injury for the non-dominant leg, but additional data should be collected and analysed on both dynamic balance and performance.  相似文献   

17.
Artistic gymnasts are frequently exposed to both low- and high-magnitude loads through impacts with the apparatus. These impact loads are thought to be associated with the high injury rates observed in gymnastics. Due to the variable apparatus and surfaces in gymnastics, impact loads during training are difficult to quantify. This study aimed to use triaxial accelerometers mounted on the back to assess impact loading during jumping and landing tasks. Twelve participants were fitted with an accelerometer on their upper and lower back, before performing a continuous hopping task, as well as drop landings and rebound jumps from various heights (37.5, 57.5, and 77.5 cm) onto a force platform. Peak resultant acceleration (PRA) was low-pass filtered with four cut-off frequencies (8, 15, 20, and 50 Hz). Filtering of PRA with the 20 Hz cut-off frequency showed the highest correlations between ground reaction force (GRF) and PRA. PRA recorded at the upper back, filtered with a 20 Hz cut-off frequency, appears to provide a good estimate of impact loading for continuous hopping and rebound jumps, but less so for drop landings since correlations between GRF and PRA were only significant when landing from 57.5 cm.  相似文献   

18.
The study examined the differences between boys and adults after an intense stretch-shortening cycle fatigue protocol on neuromechanical parameters of the lower limb. Thirteen boys (9–11 years old) and 13 adult men (22–28 years old) were tested for maximal isometric voluntary knee extension torque and drop jump (DJ) performance from 30 cm before and immediately after a fatigue protocol, consisted of 10 × 10 maximum effort vertical jumps. Three-dimensional kinematics, kinetics and electromyographic (EMG) parameters of the lower extremities muscles were recorded during DJs before and after the fatigue test. The results indicated that reduction in maximal isometric torque and jumping performance was significantly higher in adults compared to boys. Vertical ground reaction forces, contact time and maximum knee flexion increased in a greater extend in adults than in boys. In addition, preactivation, EMG agonist activity, knee joint stiffness and stretch reflex decreased more in adults than in boys at all the examined phases of jumping tasks. It is concluded that employed fatigue protocol induced acute reduction in performance and altered motor control during jumping in both age groups. However, the differences in the level of fatigue between the 2 groups could be attributed to neuromuscular, mechanical and kinematic parameters observed between groups.  相似文献   

19.
This study assessed the validity of a tri-axial accelerometer worn on the upper body to estimate peak forces during running and change-of-direction tasks. Seventeen participants completed four different running and change-of-direction tasks (0°, 45°, 90°, and 180°; five trials per condition). Peak crania-caudal and resultant acceleration was converted to force and compared against peak force plate ground reaction force (GRF) in two formats (raw and smoothed). The resultant smoothed (10 Hz) and crania-caudal raw (except 180°) accelerometer values were not significantly different to resultant and vertical GRF for all running and change-of-direction tasks, respectively. Resultant accelerometer measures showed no to strong significant correlations (r = 0.00–0.76) and moderate to large measurement errors (coefficient of variation [CV] = 11.7–23.9%). Crania-caudal accelerometer measures showed small to moderate correlations (r = ? 0.26 to 0.39) and moderate to large measurement errors (CV = 15.0–20.6%). Accelerometers, within integrated micro-technology tracking devices and worn on the upper body, can provide a relative measure of peak impact force experienced during running and two change-of-direction tasks (45° and 90°) provided that resultant smoothed values are used.  相似文献   

20.
Isometric tests have been used to assess rate of force development (RFD), however variation in testing methodologies are known to affect performance outcomes. The aim of this study was to assess the RFD in the isometric squat (ISqT) using two test protocols and two testing angles. Eleven participants (age: 26.8 ± 4.5 years, strength training experience: 7.1 ± 3.03 years) completed test and retest sessions one week apart, whereby two test protocols with respect to duration and instructions were compared. Isometric peak force (ISqTpeak) and isometric explosive force (ISqTexp) tests were assessed at two joint angles (knee flexion angle 100° and 125°). Force-time traces were sampled and subsequently analysed for RFD measures. Average and instantaneous RFD variables did not meet reliability minimum criteria in ISqTpeak at 100° or 125°. The ISqTexp test at 100° met reliability criteria in the RFD 0–200 and 0–250ms variables. The ISqTexp test at 125° met reliability criteria in the RFD 0–150, 0–200 and 0–250ms variables. Force-time characteristics were optimized at the higher knee joint angle. Average and instantaneous RFD measures obtained using a traditional peak force test do not meet basic reliability criteria. Researchers assessing multi-joint RFD should employ the explosive RFD test protocol as opposed to the traditional isometric peak force protocol.  相似文献   

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