Effects of differently induced stretch loads on neuromuscular control in drop jump exercise

The neuromuscular characteristics of the triceps surae and vastus lateralis muscles and interactions between the pre-activation of these muscles and the muscle output itself during ground contact were investigated during various types of stretch-shortening cycle muscle loading. The loading of the muscles was effected by using three different types of drop jump exercise. These jumps allowed separate modifications of the loading of the leg extensor muscles by changing the velocity of the centre of gravity (CG) or by changing directly the body mass, which was also affected by changing artificially the acceleration of the CG. It was found that the eccentric peak angular velocity of the ankle joint was related to the various precontact and eccentric parameters in all the different types of jumping exercise. The correlations were higher for the gastrocnemius muscle (P < 0.001) than for the soleus muscle (n.s., P < 0.01). In all the experimental conditions, the pre-activation of the measured muscles started well before the impact of contact with the ground. However, the duration of the pre-activation phase depended on the type of stretch exercise. The results would suggest a clear interaction between the pre-activation of the muscles and that part of the muscle output which is effected by the segmental stretch reflex system. The control mechanism of the pre-activation itself appears to be multiple in character. It seems reasonable to assume that the pre-activation is preprogrammed, but which can, however, be modified by proprioceptive, vestibular and visual inputs. Thus, the possibility of conscious modification of the expected muscle load must be considered.     

Effects of differing intensities of static stretching on jump performance

Acute bouts of static stretching have been shown to impair performance. Most published studies have incorporated static stretching that stressed the muscle(s) to the point of discomfort (POD). There are very few studies that have examined the effects of submaximal intensity (less than POD) static stretching on subsequent performance. Ten participants were pre-tested by performing two repetitions of three different stretches to assess range of motion (ROM) and two repetitions each of five different types of jumps. Following pre-testing, participants were stretched four times for 30 s each with 30 s recovery for the quadriceps, hamstrings and plantar flexors at 100% (POD), 75% and 50% of POD or a control condition. Five minutes following the stretch or control conditions, they were tested post-stretch with the same stretches and jumps as the pre-test. All three stretching intensities adversely affected jump heights. With data collapsed over stretching intensities, there were significant decreases in jump height of 4.6% (P = 0.01), 5.7% (P < 0.0001), 5.4% (P = 0.002), 3.8% (P = 0.009) and 3.6% (P = 0.008) for the drop jump, squat jump, countermovement jump (CMJ) to a knee flexion of 70°, CMJ using a preferred jump strategy and short amplitude CMJ respectively. An acute bout of maximal or submaximal intensity stretching can impair a variety of jumping styles and based on previous research, it is hypothesized that changes in muscle compliance may play a role.     

Changes in power and force generation during coupled eccentric–concentric versus concentric muscle contraction with training and aging

Age-related decline in maximal concentric muscle power is associated with frailty and functional impairments in the elderly. Compared to concentric contraction, mechanical muscle output is generally enhanced when muscles are rapidly pre-stretched (eccentric contraction), albeit less pronounced with increasing age. Exercise has been recommended to prevent loss of muscle power and function and recent guidelines indicate training program for increasing muscle power highly relevant for elderly subjects. This study examined the differences in muscle power, force and movement pattern during concentric-alone and coupled eccentric–concentric contraction and selected functional motor performances before and after 36-week multicomponent training including aerobic, strength, balance, flexibility and coordination components in elderly males. Vertical force, excursion, velocity, power and acceleration of the body center of mass were measured in two standardised vertical jumps (squatting jump, SQJ; countermovement jump, CMJ). Pre-stretch enhancement during CMJ did not improve performance [i.e., no enhanced maximal muscle power (P _peak) and jump height (JH)] compared to concentric-alone muscle contraction (SQJ). Nevertheless, pre-stretch enhancement occurred as for similar SQJ and CMJ maximal performance, elderly people employed lower mechanical work, higher mean muscle power (P _mean), shorter concentric phase duration and shorter body center of mass displacement during CMJ. Post training, CMJ P_peak, P _mean and JH increased in training group (P < 0.05) while P _peak and JH decreased in control group during the CMJ and SQJ (P < 0.05). In conclusion, long-term training counteracted the age-related decline in muscle power and functional performance observed in the control subjects, while substantial gains in muscular performance were observed in the trained elderly.     

Biomechanical analysis of structural deformation in living cells

Most tissues are subject to some form of physiological mechanical loading which results in deformation of the cells triggering intracellular mechanotransduction pathways. This response to loading is generally essential for the health of the tissue, although more pronounced deformation may result in cell and tissue damage. In order to determine the biological response of cells to loading it is necessary to understand how cells and intracellular structures deform. This paper reviews the various loading systems that have been adopted for studying cell deformation both in situ within tissue explants and in isolated cell culture systems. In particular it describes loading systems which facilitate visualisation and subsequent quantification of cell deformation. The review also describes the associated microscopy and image analysis techniques. The review focuses on deformation of chondrocytes with additional information on a variety of other cell types including neurons, red blood cells, epithelial cells and skin and muscle cells.     

Biomechanical analysis during single-leg squat in individuals with knee osteoarthritis

Backgroud: The single-leg squat (SLS) is a functional task to evaluate the abnormal movement patterns and potential neuromuscular deficits in the lower limbs. Still, it is unknown if SLS could provide information to older adults with knee osteoarthritis (KOA). The study’s objective was to analyze the EMG pattern, kinematics, and postural control in individuals with and without KOA during SLS.Methods: Participated in this study, 60 volunteers of both sexes, 30 had KOA (allocated into the KOA group - KOAG), and 30 were healthy (allocated into the Healthy Group - HG) performing the single-leg squat. Surface electromyography (EMG) was assessed for the gastrocnemius medialis (GM), biceps femoris (BF), gluteus medius (GLM), rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), and tibialis anterior (TA) in two phases (downward – P1 and upward – P2). The kinematic data was evaluated using an electrogoniometer. The center of pressure (CoP) was obtained using data collected from a force plate.Results: EMG activity was increased for GM and TA muscles during the P1 of the movement and the GM and GLM muscles during P2 of the movement. The angular displacement of the KOAG was lower when compared with the HG. There was no statistical difference for the co-contraction and postural control data.Conclusions: The SLS analysis showed that EMG activity of the muscles TA, GM, and GLM was increased in the KOAG, but this pattern could be affected by fear of movement leading to reduced knee angular displacement.     

Is knee neuromuscular activity related to anterior cruciate ligament injury risk? A pilot study

Background

There is limited evidence on neuromuscular risk factors for anterior cruciate ligament (ACL) injuries, with most work mainly focusing on hamstrings and quadriceps muscle strength. This prospective pilot study explored if neuromuscular activation patterns of the quadriceps and hamstrings during a drop vertical jump influence ACL injury risk.

3D打印个性化髋臼接骨板设计生物力学研究与分析

目的 应用三维有限元方法研究接骨板内固定疗法治疗髋臼后壁骨折,探讨接骨板与骨面不同间隙对髋臼应力分布的影响。方法 基于真实人体髋关节CT扫描数据,设计出适用于髋臼后壁骨折内固定的个性化接骨板,利用Mimics、Geomagic、Abaqus等软件构建接骨板内固定髋关节三维有限元模型,选择成人缓慢行走时单脚承重的受力状态对模型加载,分析接骨板与骨面不同间隙（0 mm、0.25 mm、0.5 mm、0.75 mm）对髋臼生物力学的影响。结果 随着接骨板与骨界面间隙的增大,接骨板与髋臼后壁碎片上所受最大应力随着间隙的增大而略微减小,但应力分布情况并没有太大的变化。结论 将本文有限元仿真结果结合临床骨治疗生物固定理念,可以发现个性化接骨板与骨界面间隙并不是越小越好,在允许范围内,应将接骨板与骨界面之间留有一定间隙。     

Biomechanical analysis of posteromedial tibial plateau split fracture fixation

The purpose of this study was to compare the biomechanical strength of four different fixation methods for a posteromedial tibial plateau split fracture. Twenty-eight tibial plateau fractures were simulated using right-sided synthetic tibiae models. Each fracture model was randomly instrumented with one of the four following constructs, anteroposterior lag-screws, an anteromedial limited contact dynamic compression plate (LC-DCP), a lateral locking plate, or a posterior T-shaped buttress plate. Vertical subsidence of the posteromedial fragment was measured from 500 N to 1500 N during biomechanical testing, the maximum load to failure was also determined.It was found that the posterior T-shaped buttress plate allowed the least subsidence of the posteromedial fragment and produced the highest mean failure load than each of the other three constructs (P = 0.00). There was no statistical significant difference between using lag screws or an anteromedial LC-DCP construct for the vertical subsidence at a 1500 N load and the load to failure (P > 0.05).This study showed that a posterior-based buttress technique is biomechanically the most stable in-vitro fixation method for posteromedial split tibial plateau fractures, with AP screws and anteromedial-based LC-DCP are not as stable for this type of fracture.     

动态咬合下牙周膜的生物力学分析

目的 分析动态咬合下加载时间、角度因素对牙周膜应力和位移的影响。方法 采用逆向工程技术建立牙周膜厚度为0.2 mm的下颌前牙—牙周膜—牙槽骨的三维模型,在与牙体长轴分别成0°、15°、30°、45°、60°、75°、90°,由颊侧向舌侧的动态咬合载荷作用下,分析不同周期下牙周膜的应力、位移变化状况。结果 在单周期下,由不同角度载荷引起的牙周膜最大残余应力极大值与最小值之比为5.5,最大位移极值之比为8.1;由5周期引起的最大位移极大值与极小值之比在1.02~1.35内随载荷角度增加;由不同角度载荷引起的最大残余应力极大值与极小值之比在1.86~3.00内随咬合周期数增加;不同角度下最大应力均集中在颈缘舌侧区域, 最大残余应力位置分布随时间在颈缘不同部位间变动;0°载荷下牙根的应力累积最严重。结论 下前牙固定桥基牙选择的临床应用中,应注意牙周膜应力累积情况以及最大残余应力分布的不确定性;临床治疗中,应避免对牙齿施加大角度载荷,尽量减少连续咬合较硬食物。     

腘腓韧带的形态学研究及生物力学分析

膝关节后外侧区有着复杂的解剖结构,后外侧区的损伤可导致膝关节后外侧旋转不稳定。本文综述了膝关节后外侧区结构之一的腘腓韧带的形成机制、形态学和生物力学研究进展及存在的问题。     

一种新型人工颞下颌关节的生物力学分析

目的　建立下颌骨髁突缺损有限元模型,研究新型人工颞下颌关节的应力分布及位移改变。 方法　运用Mimics、Geomagic、Solidworks、ANSYS软件建立含完整牙列的下颌骨右侧髁突缺损有限元模型并分析新型人工颞下颌关节在模拟咬合力加载的情况下假体及下颌骨硬组织的应力分布和位移情况。 结果　下颌骨整体等效应力值均低于20 MPa,最大形变值不超过0.05 mm。 结论　新型人工颞下颌关节能避免过大应力导致的假体断裂和骨质吸收,具有良好的生物力学特性。     

三种不同内固定治疗胫骨平台后内侧骨折的生物力学研究

目的设计一种与胫骨平台后内髁解剖形态匹配的钢板,比较其与5孔L型有限接触动力加压钢板(LCDCP)和7孔直型重建接骨板治疗胫骨平台后内侧骨折的稳定性。方法将18具胫骨平台后内侧骨折的标本随机分为3组,每组6具。其中,A组标本模型采用前内侧5孔L型LC-DCP固定,B组标本模型采用后内侧7孔直型重建接骨板固定,C组标本模型采用新设计的胫骨平台后内侧锁定钢板固定。分别测量各组标本在轴向载荷为500、1000、1500 N下的垂直位移及失效载荷。结果 A组标本分别在500、1000、1500 N下的垂直位移是(1.035±0.140)mm、(1.721±0.149)mm、(2.263±0.134)mm,B组标本分别在500、1000、1500 N下的垂直位移是(0.268±0.702)mm、(0.788±0.507)mm、(1.518±0.111)mm,C组标本分别在500、1000、1500 N下的垂直位移是(0.180±0.049)mm、(0.578±0.103)mm、(0.760±0.055)mm。在同一载荷下,三组标本骨折块垂直位移组间比较差异均有统计学意义(0.05)。A组标本失效载荷为(1234.3±56.009)N,B组标本失效载荷为(2065.8±102.098)N,C组标本失效载荷为(2544.2±92.982)N,三组间比较差异均有统计学意义(0.05)。结论新设计的胫骨平台后内侧锁定钢板在治疗胫骨平台后内侧骨折上,较5孔L型LC-DCP和7孔直型重建接骨板具有更好的生物力学优势。     

弯曲力矩对脊柱峡部的影响的生物力学分析*

目的通过分析脊椎运动节段接受相同的弯曲力矩时受力姿势对脊柱峡部的影响,以此推测引起椎弓峡部裂的危险因素。方法从八月大的幼猪颈椎截取C_(3-5)、C_6-T_1等两段双脊椎功能单位为试样,分别施加15Nm的前屈、后仰、侧弯(左、右)、前屈合并侧弯(左、右),以及后仰合并侧弯(左、右)等弯曲力矩。利用粘贴在中间椎骨左、右峡部的应变片测量峡部的应变量。利用检验分析实验数据以得出对峡部影响最大的受力姿势,归纳可能引起椎弓峡部裂的危险因素。结果椎弓峡部的应变量以后仰合并侧弯时最高(平均值935um),其次为侧弯、后仰、前屈、前屈合并侧弯以及正中姿势,平均值分别为821um、709um、117um、102um、94um。结论容易形成椎弓峡部裂的受力姿势有后仰、侧弯以及后仰合并侧弯。后仰合并侧弯与侧弯是之前较少被提出来探讨的受力姿势,当脊柱处于这两种姿势时同侧峡部的应变量明显大于对侧,证明了这两种姿势是预防椎弓峡部裂或阻止脊柱进一步滑脱时需要考虑的因素。     

Electromechanical behaviour of human muscles in vertical jumps

Summary The relationships of muscle structure to the potentiation of myoelectrical activity and to the use of prestretching in five lower limb muscles were studied in different vertical jumping conditions. The subjects for the study were six male students, divided according to the muscle fiber distribution in m. vastus lateralis into fast and slow groups. The subjects performed vertical jumps (1) from a static squatting position (SJ), (2) with a preliminary counter movement (CMJ) and (3) after dropping (DJ) from five different heights. Myoelectrical (EMG) activity was recorded from mm. gluteus maximus, vastus lateralis, vastus medialis, rectus femoris and gastrocnemius in each jumping condition and integrated (IEMG) for the eccentric and concentric phases of contact. EMG activity showed potentiation during the eccentric phase of movement when compared to the concentric phase. The fast and slow groups did not differ significantly in this respect, whereas in DJ conditions the relative (% from SJ) height of rise of the center of gravity was greater in the slow than in the fast group. The result indicated that the utilization of elastic energy during jumping was possible better in subjects having a high percentage of slow twitch muscle fibres in their vastus lateralis muscles.     

Biomechanical study of tarsometatarsal joint fusion using finite element analysis

Complications of surgeries in foot and ankle bring patients with severe sufferings. Sufficient understanding of the internal biomechanical information such as stress distribution, contact pressure, and deformation is critical to estimate the effectiveness of surgical treatments and avoid complications. Foot and ankle is an intricate and synergetic system, and localized intervention may alter the functions to the adjacent components. The aim of this study was to estimate biomechanical effects of the TMT joint fusion using comprehensive finite element (FE) analysis. A foot and ankle model consists of 28 bones, 72 ligaments, and plantar fascia with soft tissues embracing all the segments. Kinematic information and ground reaction force during gait were obtained from motion analysis. Three gait instants namely the first peak, second peak and mid-stance were simulated in a normal foot and a foot with TMT joint fusion. It was found that contact pressure on plantar foot increased by 0.42%, 19% and 37%, respectively after TMT fusion compared with normal foot walking. Navico-cuneiform and fifth meta-cuboid joints sustained 27% and 40% increase in contact pressure at second peak, implying potential risk of joint problems such as arthritis. Von Mises stress in the second metatarsal bone increased by 22% at midstance, making it susceptible to stress fracture. This study provides biomechanical information for understanding the possible consequences of TMT joint fusion.     

Effect of wearing a knee brace or sleeve on the knee joint and anterior cruciate ligament force during drop jumps: A clinical intervention study

Background

Knee braces are considered to be extremely useful tools in reducing the shear force of knee joints for non-contact anterior cruciate ligament (ACL) injury prevention. However, the effectiveness of sports knee braces and sleeves remains to be identified. Therefore, the purpose of this study was to evaluate the effectiveness of wearing commercialized sports knee braces and sleeves on knee kinematics, kinetics, and ACL force during drop jumps using musculoskeletal modeling analysis.

Method to evaluate the skill level in fast locomotion through myoelectric and kinetic signal analysis

The paper describes a method aimed at providing objective diagnostic testing of skilled locomotor stereotypes. Bioelectric muscle activity indices and ground reaction force data are used to represent a movement structure, in a schematised way, using discrete states in time. Athletes were asked to perform one specific movement structure: a backward somersault from the standing position. Mathematical analyses of measured signals reveal the significance, for the skill level evaluation, of parameters reflecting the impulsive take-off force waveform and the symmetry in EMG activity of ankle extensor muscles, which therefore might be used as diagnostic criteria. Within technical limitations, this approach may also be applied to other locomotor patterns and possibly to monitor the progress in motorics in pathological locomotion. EMG telemetry could significantly enhance the method's scope.     

Scapular muscle activation and co-activation following a fatigue task

Scapular muscles precisely move the scapulothoracic articulation and if fatigued may contribute to pathology. Fatigue of serratus anterior may be a mechanism for shoulder pathology by altering scapula motions and requiring compensation by other shoulder muscles. A total of 28 asymptomatic subjects performed a task to fatigue the serratus anterior, while muscle activity was recorded from three muscles. Mean normalized activation levels and activation ratios were examined before and after the fatigue task during arm elevation and lowering. All muscles demonstrated meaningful declines in the median frequency of the electromyographic signal during the task. Following the task, only the upper trapezius had higher mean activation levels (mean difference 10.79% MVIC), while the serratus anterior/lower trapezius activation ratio was altered (mean difference −0.3). Higher mean upper trapezius activation may be compensatory for fatigue of other shoulder muscles and may reflect fiber type or central control mechanisms. Serratus anterior eccentric endurance training may be beneficial for the prevention of shoulder pathology.     

基于表面肌电信号和动作捕捉的上肢运动疲劳分析EI北大核心CSCD

目前,上肢运动的疲劳状态监测,一般单纯依赖表面肌电信号(sEMG)对疲劳进行识别和分类,导致结果不稳定,存在一定局限。为此,本文将sEMG信号识别与动作捕捉技术引入到疲劳状态监测过程中,提出了一种融合改进的肌电疲劳阈值算法与生物力学分析的疲劳分析方法。本研究通过右上肢负载屈肘试验,同步采集肱二头肌sEMG信号与上肢动作捕捉数据,并同时运用柏格(Borg)疲劳度主观自觉量表记录受试者疲劳感受。然后,将融合改进的肌电疲劳阈值算法和生物力学分析的疲劳分析方法与平均功率频率(MPF)、谱矩比(SMR)、模糊近似熵(fApEn)、Lempel-Ziv复杂度(LZC)四种单一评价指标疲劳评价方法的试验结果进行对比。试验结果表明,本文方法对总体疲劳状态识别率结果达到98.6%,对轻松、过渡、疲劳三种状态的识别率分别达到97%、100%、99%,较其他方法更有优势。本文研究结果证明,本文方法在上肢运动过程中能够有效预防过度训练引起的二次损伤,对于疲劳监护具有重要意义。     

人工髋关节脱位失效的生物力学分析与推理(附专家点评)

目的研究人工髋关节置换术后脱位失效力学机理以及在术后各时间段引发脱位的具体原因,提出对临床中发生的脱位事件进行失效诊断的具体方法。方法通过建立脱位模型对脱位过程的生物力学机理进行研究,分析脱位失效与临床、产品设计和患者三方面因素的关系。结果提出脱位分析推理路线图,开发并验证专门用于脱位分析的软件工具。结论髋关节脱位失效临床案例分析表明,该人工髋关节脱位分析方法与工具能够帮助判断具体脱位事件的产生原因,确定假体设计、术中植入位置与脱位事件之间的关系。同时可在术前确定假体最佳植入位置并分析脱位发生的可能风险,对假体设计也有指导作用。