The effect of a psyching strategy on neuromuscular activation and force production in strength-trained men

Force and electromyographic (EMG) activity of the biceps and triceps brachii were measured in 15 strength-trained men during maximal isometric action of the forearm flexors, with the elbow at 90 degrees, following 20-s periods of psyching (PSY), reading aloud (RA), and mental arithmetic (MA). Perceived arousal and attentional focus ratings for PSY were greater than those obtained for RA and MA, which were undifferentiated. Perceived effort, biceps and triceps EMG, and maximal force did not differ across conditions. Therefore, in highly trained men under conditions of brief exertion, when the biomechanics of the muscular action were controlled, psyching resulted in a perception of enhanced readiness but did not influence force or muscular activation differently from psychological states that were preceded by distraction.     

A protocol for measuring the direct effect of cycling on neuromuscular control of running in triathletes

Abstract

The direct effects of cycling on movement and muscle recruitment patterns (neuromuscular control) during running are unknown but critical to success in triathlon. We outline and test a new protocol for investigating the direct influence of cycling on neuromuscular control during running. Leg movement (three-dimensional kinematics) and muscle recruitment (surface electromyography, EMG) were compared between a control run (no prior exercise) and a 30-min transition run that was preceded by 20 min of cycling. We conducted three experiments investigating: (a) the repeatability (between-day reliability) of the protocol; (b) the ability of the protocol to investigate, in highly trained national or international triathletes, the direct influence of cycling on neuromuscular control during running independent of neuromuscular fatigue; and (c) the ability of the protocol to provide a control, or baseline, measure of neuromuscular control (determined using a measure of stability) without causing fatigue. Kinematic and EMG measures of neuromuscular control during running showed moderate to high repeatability: mean coefficients of multiple correlation for repeatability of EMG and kinematics were 0.816 ± 0.014 and 0.911 ± 0.031, respectively. The protocol provided a robust baseline measure of neuromuscular control during running without causing neuromuscular fatigue (coefficients of multiple correlation for stability of EMG and kinematics were 0.827 ± 0.023 and 0.862 ± 0.054), while EMG and force data provided no evidence of fatigue. The protocol outlined here is repeatable and can be used to measure any direct influence of cycling on neuromuscular control during running.     

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.     

地表面倾斜度与踝关节护具对垂直着地运动中地面反作用力、踝关节运动学和动力学的效应

研究背景：现有研究文献尚无有关在着地过程中不同表面倾斜度和踝关节护具效应的运动学、动力学和地面反作用力的综合数据。通过对比25°斜面和平面的着地以及使用和不使用踝关节护具情况下来检测踝关节的生物力学特性。研究方法： 11名健康受试者[年龄：（24.6±3.5）岁,身高：（24.6±0.10）m,质量：（65.6±14.9）kg）参与本次研究。受试者在4个动态运动条件下各进行5五次实验：从0.45米高处垂直下落至25°的斜面（IS）或平面（FS）上,使用或不使用半刚性踝关节护具,同时采集三维运动学和测力台地面反作用力数据。利用2×2(表面X踝关节护具)的重复测量方差分析来评估选定的变量。研究结果：与平面着地相比,斜面着地造成较小的垂直和内侧地面反作用力峰值。研究还发现踝关节背曲运动范围、着地角度和背曲速度、最大外翻与跖曲角速度提高,但产生了更大内翻角度和运动范围、着地内翻速度和最大跖曲力矩。踝关节护具在斜面着地时减少了达到地面反作用力第二垂直峰值的时间、着地角度、背曲速度、最大外翻和跖曲速度,但增加了跖曲力矩的最大值。研究结论：斜面增加踝关节额状面的运动范围和踝关节负荷。但是,就斜面着地而言,踝关节护具对踝关节额状面的运动范围和踝关节负荷的影响是相当有限的。     

The effect of knee angle on the external validity of isometric measures of lower body neuromuscular function

The aim of this study was to evaluate the effect of varying knee angle (120° and 90°) on the external validity of an isometric leg press test with reference to vertical jump performance. Isometric peak force (PF 120 and PF 90 ), rate of force development (RFD 120 and RFD 90 ), and maximum height reached with a squat jump and counter-movement jump were measured in 14 males. Although RFD 120 was significantly correlated with squat jump and counter-movement jump performance ( r = 0.71 and 0.69), and the correlations with PF 120 approached statistical significance ( r = 0.53 and 0.50), neither PF 90 nor RFD 90 was significantly related to vertical jump performance. Furthermore, although both RFD 120 and PF 120 were significantly different between the best five and the worst five jumpers, RFD 90 and PF 90 did not differentiate between individuals' vertical jump performance. We conclude that the choice of joint angle affects the external validity of isometric strength testing. Based on our results, we recommend accurate control of biomechanical specificity and assessment at different angles to find the position at which isometric strength testing is most comfortable.     

The effect of knee angle on the external validity of isometric measures of lower body neuromuscular function

The aim of this study was to evaluate the effect of varying knee angle (120 degrees and 90 degrees) on the external validity of an isometric leg press test with reference to vertical jump performance. Isometric peak force (PF120 and PF90), rate of force development (RFD120 and RFD90), and maximum height reached with a squat jump and counter-movement jump were measured in 14 males. Although RFD120 was significantly correlated with squat jump and counter-movement jump performance (r = 0.71 and 0.69), and the correlations with PF120 approached statistical significance (r = 0.53 and 0.50), neither PF90 nor RFD90 was significantly related to vertical jump performance. Furthermore, although both RFD120 and PF120 were significantly different between the best five and the worst five jumpers, RFD90 and PF90 did not differentiate between individuals' vertical jump performance. We conclude that the choice of joint angle affects the external validity of isometric strength testing. Based on our results, we recommend accurate control of biomechanical specificity and assessment at different angles to find the position at which isometric strength testing is most comfortable.     

The effect of sex and localised fatigue on triceps surae musculoarticular stiffness

Purpose: The main purpose of this study was to investigate the influence of fatigue on musculoarticular stiffness (MAS) of the ankle joint across sexes. Methods: Twenty-seven males and 26 females participated in the study. After baseline assessment of MAS and related variables, localised fatigue was induced in triceps surae using the standing heel-rise test during which the subjects were instructed to lift and drop the heel at a frequency of 0.5?Hz. When subjects were unable to continue due to exhaustion the test was terminated and another MAS test was performed soon after. Results: Significant higher triceps surae MAS was found in men compared to women (p?p??1 and from 14.5 to 13.9?KN?m^?1 in men and women, respectively. Percentage changes revealed, however, that in relative terms the changes in all the variables evaluated were similar (p?>?.01) between sexes, with MAS less than 5%. Conclusion: Despite the sex-related differences at baseline, fatigue seems to affect biomechanical properties of the ankle joint similarly in men and women.     

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.     

踝关节稳定程度差异对侧跳落地缓冲模式影响的研究

目的:探讨不同踝关节稳定程度对侧跳落地缓冲时姿势稳定策略与神经肌肉控制的影响。方法:36名男性大学高水平运动员为受试者,按照踝关节不稳定程度分为12人健康组(CON)、12人隐患组(LAT)和12人不稳定组(CAI),以随机顺序执行4次单足连续侧跳动作,涉及外侧侧向跳动作(SHL)与内侧侧向跳动作(SHM)。使用VICON三维动作捕捉系统、KISTLER测力板与DELSYS无线表面肌电收集下肢生物力学参数;使用独立样本单因子方差分析(one-way ANOVA)比较各组在起跳后落地5个阶段的下肢关节运动学参数、动力学参数及肌肉激活水平。结果:1)下肢矢状面肌群激活程度与踝关节肌肉共同收缩率,对CAI组的动态姿势稳定扮演重要角色,以SHL落地的踝关节外翻动作能降低踝关节内翻扭伤风险;2)在SHL落地模式下,CAI组髋关节内收动作可能会引起踝关节内翻动作,侧跳落地的踝关节内翻角速度出现较早且快速的特征是CAI组反复扭伤的关键;3)踝关节策略主要影响压力中心(COP)参数,髋关节策略则能改变质量中心(COM);CON组侧跳的落地缓冲与姿势控制能力不及CAI稳定;SHM落地模式是踝关节内翻扭伤的高风险动作。结论:CAI组运动员即便在扭伤康复后,仍存在再次扭伤的可能,可针对踝关节活动范围与神经肌肉控制进行强化与训练,避免反复损伤。     

Effects of neuromuscular fatigue on perceptual-cognitive skills between genders in the contribution to the knee joint loading during side-stepping tasks

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.     

Multi-joint rate of force development testing protocol affects reliability and the smallest detectible difference

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 (ISqT^peak) and isometric explosive force (ISqT^exp) 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 ISqT^peak at 100° or 125°. The ISqT^exp test at 100° met reliability criteria in the RFD 0–200 and 0–250ms variables. The ISqT^exp 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.     

推拿加中国炙治踝关节扭伤疗效的探索

踝关节扭伤是临床常见病、多发病,一般多见于体育活动时的跌扑闪失,它影响患者工作(训练)、学习和日常生活.根据临床病例实况,采用针对性的推拿手法,以改善和调节患部;辅之通经活络,活血祛瘀,消肿止痛的中国炙(热敷)治疗,操作简便、见效快,经60例治疗实验,疗效显著.     

Acute and chronic effects of foam rolling vs eccentric exercise on ROM and force output of the plantar flexors

Foam rolling and eccentric exercise interventions have been demonstrated to improve range of motion (ROM). However, these two modalities have not been directly compared. Twenty-three academy soccer players (age: 18 ± 1; height: 1.74 ± 0.08 m; body mass: 69.3 ± 7.5 kg) were randomly allocated to either a foam rolling (FR) or eccentric exercise intervention designed to improve dorsiflexion ROM. Participants performed the intervention daily for a duration of four weeks. Measurements of dorsiflexion ROM, isometric plantar flexion torque and drop jump reactive strength index were taken at baseline (pre-intervention) and at three subsequent time-points (30-min post, 24-hours post and 4-weeks post). A significant time x group interaction effect was observed for dorsiflexion (P = 0.036), but not for torque or reactive strength index. For dorsiflexion, there was a significant increase in both acute (30-min; P < 0.001) and chronic (4-week; P < 0.001) ROM for the eccentric group, whilst FR exhibited only an acute improvement (P < 0.001). Eccentric training would appear a more efficacious modality than foam rolling for improving dorsiflexion ROM in elite academy soccer players.     

The effect of induced alkalosis and submaximal cycling on neuromuscular response during sustained isometric contraction

Abstract

The aim of this study was to determine if inducing metabolic alkalosis would alter neuromuscular control after 50 min of standardized submaximal cycling. Eight trained male cyclists (mean age 32 years, s = 7; [Vdot]O_2max 62 ml · kg^?1 · min^?1, s = 8) ingested capsules containing either CaCO₃ (placebo) or NaHCO₃ (0.3 g · kg^?1 body mass) in eight doses over 2 h on two separate occasions, commencing 3 h before exercise. Participants performed three maximal isometric voluntary contractions (MVC) of the knee extensors while determining the central activation ratio by superimposing electrical stimulation both pre-ingestion and post-exercise, followed by a 50-s sustained maximal contraction in which force, EMG amplitude, and muscle fibre conduction velocity were assessed. Plasma pH, blood base excess, and plasma HCO₃ were higher (P < 0.01) during the NaHCO₃ trial. After cycling, muscle fibre conduction velocity was higher (P < 0.05) during the 50-s sustained maximal contraction with NaHCO₃ than with placebo (5.1 m · s^?1, s = 0.4 vs. 4.2 m · s^?1, s = 0.4) while the EMG amplitude remained the same. Force decline rate was less (P < 0.05) during alkalosis-sustained maximal contraction and no differences were shown in central activation ratio. These data indicate that induced metabolic alkalosis can increase muscle fibre conduction velocity following prolonged submaximal cycling.     

Impact of hockey skate design on ankle motion and force production

Dynamic forces and range of motion (ROM) were measured during on-ice skating using a standard hockey skate and a modified skate (MS) with an altered tendon guard and eyelet configuration. The objective of this study was to determine if these modifications resulted in biomechanical and performance changes during on-ice skating skills. The right skate of each type was instrumented with a calibrated strain gauge force transducer system to measure medial?Clateral and vertical forces during ice skating. In addition, a goniometer was placed about the ankle and rear foot to measure ROM during skating. Ten subjects executed three skills: forward skating, crossovers inside foot and crossovers outside foot. The MS demonstrated significant gains of 5°?C9° in dorsi-plantarflexion ROM (p?<?0.05). Total peak force occurred later during plantarflexion, suggesting a more prolonged and effective force generation with the MS during a given skating stride. A 14?C20?% increase (p?>?0.05) in mean work and power output was noted with the MS, although no improved times were observed during the skating skills. Potentially, some players may need a period of familiarization to take advantage of the design alterations of the MS.     

大学体育院系普修跨栏跑教学中踝部损伤的原因及预防

本文通过调查大学体育院系普修跨栏跑运动中,踝部发生损伤的机率及其损伤发生的阶段。从踝部的解剖结构特点,分析踝部运动损伤的原因,从中找出规律,并针对原因提出一些预防的方法,为教师在跨栏跑教学训练中减少学生踝部运动损伤提供理论依据。     

运动性踝关节韧带损伤原因分析及预防治疗

通过对在北医三院及北体大校医院就诊的164例运动性踝关节韧带损伤患者的受伤原因及治疗过程进行分析论证,提出预防及治疗的建议.     

步态生物力学研究进展

阐述了步态生物力学的时间参数、空间参数、时－空参数和力学参数的研究状况，以及各参 数在行走功能评定、疗效评定、指导治疗和行走辅助装置设计等方面的应用。     

浅谈羽毛球运动员踝关节损伤的原因与防治

羽毛球运动员在高强度训练和高密度比赛环境下,由于其运动特点,极易造成踝关节的各种损伤,本文根据羽毛球的运动特点,以踝关节的生理结构、运动学特点等为依据,以鲁东大学运动系羽毛球专选课学生为研究对象,运用文献资料法、访谈法、总结归纳法等方法对踝关节损伤进行简要研究和提出可行性防治建议。