Independence of reaction time and response force control during isometric leg extension

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.     

不同水平短跑运动员途中跑支撑反作用力研究

运用运动学、动力学同步测试分析的方法,揭示了不同水平短跑运动员支撑过程中支撑反作用力和人体运动学参数的差异及其相互关系,以认识短跑途中跑技术和支撑反作用力的特征。     

国内外优秀短跨运动员起跑反应时与成绩的研究

采用文献资料法、数理统计法,对近年来世界优秀男子短跨起跑反应时和成绩进行研究,阐述了反应时的快慢对短跨不同水平成绩的获得有不同程度影响,旨在为指导教练员们科学训练提供参考。     

Explosive force production during isometric squats correlates with athletic performance in rugby union players

Abstract

This study investigated the association between explosive force production during isometric squats and athletic performance (sprint time and countermovement jump height). Sprint time (5 and 20 m) and jump height were recorded in 18 male elite-standard varsity rugby union players. Participants also completed a series of maximal- and explosive-isometric squats to measure maximal force and explosive force at 50-ms intervals up to 250 ms from force onset. Sprint performance was related to early phase (≤100 ms) explosive force normalised to maximal force (5 m, r = ?0.63, P = 0.005; and 20 m, r = ?0.54, P = 0.020), but jump height was related to later phase (>100 ms) absolute explosive force (0.51 < r < 0.61; 0.006 < P < 0.035). When participants were separated for 5-m sprint time (< or ≥ 1s), the faster group had greater normalised explosive force in the first 150 ms of explosive-isometric squats (33–67%; 0.001 < P < 0.017). The results suggest that explosive force production during isometric squats was associated with athletic performance. Specifically, sprint performance was most strongly related to the proportion of maximal force achieved in the initial phase of explosive-isometric squats, whilst jump height was most strongly related to absolute force in the later phase of the explosive-isometric squats.     

Postural stability,clicker reaction time and bow draw force predict performance in elite recurve archery

Recurve archery is an Olympic sport that requires extreme precision, upper body strength and endurance. The purpose of this research was to quantify how postural stability variables both pre- and post-arrow release, draw force, flight time, arrow length and clicker reaction time, collectively, impacted on the performance or scoring outcomes in elite recurve archery athletes. Thirty-nine elite-level recurve archers (23 male and 16 female; mean age?=?24.7?±?7.3 years) from four different countries volunteered to participate in this study prior to competing at a World Cup event. An AMTI force platform (1000Hz) was used to obtain centre of pressure (COP) measurements 1s prior to arrow release and 0.5s post-arrow release. High-speed footage (200Hz) allowed for calculation of arrow flight time and score. Results identified clicker reaction time, draw force and maximum sway speed as the variables that best predicted shot performance. Specifically, reduced clicker reaction time, greater bow draw force and reduced postural sway speed post-arrow release were predictors of higher scoring shots. It is suggested that future research should focus on investigating shoulder muscle tremors at full draw in relation to clicker reaction time, and the effect of upper body strength interventions (specifically targeting the musculature around the shoulder girdle) on performance in recurve archers.     

Effects of load on ground reaction force and lower limb kinematics during concentric squats

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1?±?0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67?±?0.20 to 3.21?±?0.29 times body weight and increased significantly as external load increased (P?<?0.05). Bar linear velocity ranged from 0.54?±?0.11 to 2.50?±?0.50?m?·?s^?1 and decreased significantly with increasing external load (P?<?0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P?<?0.05). The force?–?barbell velocity curves were fitted using linear models with coefficients (r ²) ranging from 0.59 to 0.96. The results suggest that maximal force exertion during squat exercises is not achieved at the same position of the lower body as external load is increased. In contrast, joint velocity coordination does not change as load is increased. The force?–?velocity relationship was linear and independent from the set of data used for its determination.     

Control of propulsion and body lift during the first two stances of sprint running: a simulation study

The aim of this study was to relate the contribution of lower limb joint moments and individual muscle forces to the body centre of mass (COM) vertical and horizontal acceleration during the initial two steps of sprint running. Start performance of seven well-trained sprinters was recorded using an optoelectronic motion analysis system and two force plates. Participant-specific torque-driven and muscle-driven simulations were conducted in OpenSim to quantify, respectively, the contributions of the individual joints and muscles to body propulsion and lift. The ankle is the major contributor to both actions during the first two stances, with an even larger contribution in the second compared to the first stance. Biarticular gastrocnemius is the main muscle contributor to propulsion in the second stance. The contribution of the hip and knee depends highly on the position of the athlete: During the first stance, where the athlete runs in a forward bending position, the knee contributes primarily to body lift and the hip contributes to propulsion and body lift. In conclusion, a small increase in ankle power generation seems to affect the body COM acceleration, whereas increases in hip and knee power generation tend to affect acceleration less.     

Comparison of crossover and jab step start techniques for base stealing in baseball

Base stealing is an important tactic for increasing the chance of scoring in baseball. This study aimed to compare the crossover step (CS) and jab step (JS) starts for base stealing start performance and to clarify the differences between CS and JS starts in terms of three-dimensional lower extremity joint kinetics. Twelve male baseball players performed CS and JS starts, during which their motion and the force they applied to the ground were simultaneously recorded using a motion-capture system and two force platforms. The results showed that the normalised average forward external power, the average forward–backward force exerted by the left leg, and the forward velocities of the whole body centre of gravity generated by both legs and the left leg were significantly higher for the JS start than for the CS start. Moreover, the positive work done by hip extension during the left leg push-off was two-times greater for the JS start than the CS start. In conclusion, this study has demonstrated that the jab step start may be the better technique for a base stealing start and that greater positive work produced by left hip extension is probably responsible for producing its larger forward ground reaction force.     

Effect of defence response time during lunge in foil fencing

The aim of this study was to analyse the effect of stimulus change timing on reaction response time parameters, horizontal velocity of the centre of mass (CM) and precision during offensive actions in fencing. Twelve fencers from the Spanish National Foil Team were included in the study. Two 500 Hz force plates were used to register the horizontal component of the reaction force while a 3D video camera set at 250 Hz recorded the spatial position of 11 body markers and a projector connected to a programmed stopwatch projected a moving target (stimulus) on a screen. When the circle (target) appeared in the centre of the plastron, fencers had to execute a step-forward-lunge as fast as possible, trying to touch the circle with the tip of the foil. During the lunge, the position of the target could randomly shift or not to three different positions. The stimulus change was performed randomly at four different times with a progressive delay. The results show that target changes did not have any effect when they occurred at the beginning of the movement sequence. However, when the target change was delayed, reaction and movement times increased and the technical execution of the lunge changed, leading to more errors.     

Force-Time Characteristics and Running Velocity of Male Sprinters during the Acceleration Phase of Sprinting

Abstract

In an effort to investigate the force-time characteristics during the acceleration phase of the sprint start, eight male sprinters were used as subjects. Runs up to 3 m were analyzed from film, and force-time parameters were measured on a force platform. In a starting stance the reaction time of the group was .118 ± .016 s and the force production lasted .342 ± .022 s. The maximal resultant force at the moment of maximal horizontal force was 19.3 ± 2.2 N x kg¹, and the direction of the force was 32 ± 7°. In the very last instant before leaving the blocks the velocity of the center of gravity was 3.46 ± .32 m x s^?1. In the first contact after leaving the blocks there was a braking phase (.022 ± .005 s in duration) during which the average horizontal force was ?153 ± 67 N. The braking phase was observed despite the body center of gravity being horizontally ahead by .13 ± . 05 m with respect to the first contact point. The percentage of deceleration in running velocity during that phase was 4.8 ± 2.9%. In the propulsion phase the average horizontal force was great (526 ± 75 N), and it was produced for a relatively long time (.171 ± .035 s). Significant correlation coefficients were observed between force production and running velocity. These results suggest that braking/propulsion phases occur immediately after the block phase and that muscle strength strongly affects running velocity in the sprint start.     

Modelling error distribution in the ground reaction force during an induced-acceleration analysis of running in rear-foot strikers

The objective of this study was to develop and evaluate a methodology for quantifying the contributions of modelling error terms, as well as individual joint torque, gravitational force and motion-dependent terms, to the generation of ground reaction force (GRF), whose true value can be measured with high accuracy using a force platform. Dynamic contributions to the GRF were derived from the combination of (1) the equations of motion for the individual segments, (2) the equations for constraint conditions arising from the connection of adjacent segments at joints, and (3) the equations for anatomical constraint axes at certain joints. The contribution of the error term was divided into four components caused by fluctuation of segment lengths, geometric variation in the constraint joint axes, and residual joint force and moment errors. The proposed methodology was applied to the running motion of thirteen rear-foot strikers at a constant speed of 3.3?m/s. Modelling errors arose primarily from fluctuations in support leg segment lengths and rapid movement of the virtual joint between the foot and ground during the first 20% of stance phase. The magnitudes of these error contributions to the vertical and anterior/posterior components of the GRF are presented alongside the non-error contributions, of which the joint torque term was the largest.     

Effects of oncoming target velocities on rapid force production and accuracy of force production intensity and timing

The present study aimed to clarify the effects of oncoming target velocities on the ability of rapid force production and accuracy and variability of simultaneous control of both force production intensity and timing. Twenty male participants (age: 21.0 ± 1.4 years) performed rapid gripping with a handgrip dynamometer to coincide with the arrival of an oncoming target by using a horizontal electronic trackway. The oncoming target velocities were 4, 8, and 12 m · s^?1, which were randomly produced. The grip force required was 30% of the maximal voluntary contraction. Although the peak force (Pf) and rate of force development (RFD) increased with increasing target velocity, the value of the RFD to Pf ratio was constant across the 3 target velocities. The accuracy of both force production intensity and timing decreased at higher target velocities. Moreover, the intrapersonal variability in temporal parameters was lower in the fast target velocity condition, but constant variability in 3 target velocities was observed in force intensity parameters. These results suggest that oncoming target velocity does not intrinsically affect the ability for rapid force production. However, the oncoming target velocity affects accuracy and variability of force production intensity and timing during rapid force production.     

对跆拳道运动员“感知觉”“反应和反应时”及心理特征的分析

对跆拳道运动员的感知觉、反应和反应时及心理特征进行了分析,认为上述心理特征直接影响运动员技术学习的快慢、训练水平的高低和比赛发挥的好坏。     

Static and dynamic single leg postural control performance during dual-task paradigms

Combining dynamic postural control assessments and cognitive tasks may give clinicians a more accurate indication of postural control under sport-like conditions compared to single-task assessments. We examined postural control, cognitive and squatting performance of healthy individuals during static and dynamic postural control assessments in single- and dual-task paradigms. Thirty participants (female = 22, male = 8; age = 20.8 ± 1.6 years, height = 157.9 ± 13.0 cm, mass = 67.8 ± 20.6 kg) completed single-leg stance and single-leg squat assessments on a force plate individually (single-task) and concurrently (dual-task) with two cognitive assessments, a modified Stroop test and the Brooks Spatial Memory Test. Outcomes included centre of pressure speed, 95% confidence ellipse, squat depth and speed and cognitive test measures (percentage of correct answers and reaction time). Postural control performance varied between postural control assessments and testing paradigms. Participants did not squat as deep and squatted slower (P < 0.001) during dual-task paradigms (≤12.69 ± 3.4 cm squat depth, ≤16.20 ± 4.6 cm · s^?1 squat speed) compared to single-task paradigms (14.57 ± 3.6 cm squat depth, 19.65 ± 5.5 cm · s^?1 squat speed). The percentage of correct answers did not change across testing conditions, but Stroop reaction time (725.81 ± 59.2 ms; F_2,58 = 7.725, P = 0.001) was slowest during single-leg squats compared to baseline (691.64 ± 80.1 ms; P = 0.038) and single-task paradigms (681.33 ± 51.5 ms; P < 0.001). Dynamic dual-task assessments may be more challenging to the postural control system and may better represent postural control performance during dynamic activities.     

Validation of a wireless shoe insole for ground reaction force measurement

Ground reaction force measurements are a fundamental element of kinetic analyses of locomotion, yet they are traditionally constrained to laboratory settings or stationary frames. This study assessed the validity and reliability of a new wireless in-shoe system (Novel Loadsol/Pedoped) for field-based ground reaction force measurement in hopping, walking, and running. Twenty participants bilaterally hopped on a force plate and walked (5 km/hr) and ran (10 km/hr) on an instrumented treadmill on two separate days while wearing the insoles. GRFs were recorded simultaneously on each respective system. Peak GRF in hopping and peak GRF, contact time (CT), and impulse (IMP) in walking and running were compared on a per-hop and step-by-step basis. In hopping, the insoles demonstrated excellent agreement with the force plate (ICC: 0.96). In walking and running, the insoles demonstrated good-to-excellent agreement with the treadmill across all measures (ICCs: 0.88–0.96) and were reliable across sessions (ICCs within 0.00–0.03). A separate verification study with ten participants was conducted to assess a correction algorithm for further agreement improvement but demonstrated little meaningful change in systemic agreements. These results indicated that the Novel Loadsol system is a valid and reliable tool for wireless ground reaction force measurement in hopping, walking, and running.     

不同注意焦点训练对短跑起跑表现的影响

短跑起跑阶段需要对外部信号集中注意并快速反应,以产生最佳运动表现。因此,本研究假设：狭窄外部注意焦点导向会对短跑选手的起跑表现产生有益影响。研究基于短跑起跑的三个动力学阶段（实际反应时阶段,蹬起跑器反应动作时阶段和加速跑阶段）,测试新手和精英短跑选手在一段10M的短跑起跑中,在3种注意焦点导向条件下（狭窄外部注意导向、狭窄内部注意导向、中性指导语）的起跑表现。研究结果显示：在狭窄外部注意导向条件中,实际反应时、反应动作时和起跑加速时均显著短于狭窄内部注意焦点导向条件中的时间。研究结果证实：（1）根据信号而启动的短距离快速移动项目中,狭窄外部注意焦点导向会产生有益影响。（2）不同的注意焦点导向会影响动作表现。     

第16届亚运会100m跑男、女运动员起跑反应时的差异研究

以第16届亚运会100 m跑56名男、女运动员的起跑后蹬时间的压力曲线为研究对象,将男、女运动员的起跑反应时分成3个时间段进行对比分析。研究结果表明:男、女运动员起跑反应时具有显著性差异;蹬力达到阈值时间(反应动作时间)是造成男、女运动员起跑反应时具有显著性差异的重要原因;力量与爆发力是造成男、女运动员蹬力达到阈值时间(反应动作时间)具有显著性差异的重要因素;相对于男运动员40 kg压力阈值,女运动员合理的压力阈值是25 kg;电子起跑监测系统中,合理的起跑反应时限应是国际田联起跑反应时限100 ms的基础上加上蹬力达到阈值时间。     

The acute effects of static stretching on peak force,peak rate of force development and muscle activity during single- and multiple-joint actions in older women

Abstract

The present study investigated the acute effects of static stretching on peak force, peak rate of force development and integrated electromyography (iEMG) in 27 older women (65 ± 4 years; 69 ± 9 kg; 157 ± 1 cm; 28 ± 4 kg · m^?2). The participants were tested during two exercises (leg press and knee extension) after two conditions: stretching and control. The data were collected on four days (counterbalanced with a 24-hour rest period). In the stretching condition, the quadriceps muscle was stretched (knee flexion) for three sets of 30 s with 30 s rest intervals. No significant difference was detected for peak force and peak rate of force development during the single- and multiple-joint exercises, regardless of the following interactions: condition (stretching and control) vs. time (pre x post x 10 x 20 x 30 minutes post; P > 0.05) and exercise vs. time (P > 0.05). Additionally, no significant interaction was found for the iEMG activity (condition vs. time; P > 0.05) in the single- and multiple-joint exercises. In conclusion, a small amount of stretching of an agonist muscle (quadriceps) did not affect the peak force, peak rate of force development and EMG activity in older women during single- and multiple-joint exercises.     

Running quietly reduces ground reaction force and vertical loading rate and alters foot strike technique

This study aimed to determine if a quantifiable relationship exists between the peak sound amplitude and peak vertical ground reaction force (vGRF) and vertical loading rate during running. It also investigated whether differences in peak sound amplitude, contact time, lower limb kinematics, kinetics and foot strike technique existed when participants were verbally instructed to run quietly compared to their normal running. A total of 26 males completed running trials for two sound conditions: normal running and quiet running. Simple linear regressions revealed no significant relationships between impact sound and peak vGRF in the normal and quiet conditions and vertical loading rate in the normal condition. t-Tests revealed significant within-subject decreases in peak sound, peak vGRF and vertical loading rate during the quiet compared to the normal running condition. During the normal running condition, 15.4% of participants utilised a non-rearfoot strike technique compared to 76.9% in the quiet condition, which was corroborated by an increased ankle plantarflexion angle at initial contact. This study demonstrated that quieter impact sound is not directly associated with a lower peak vGRF or vertical loading rate. However, given the instructions to run quietly, participants effectively reduced peak impact sound, peak vGRF and vertical loading rate.     

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.