Measurement device for ankle joint kinematic and dynamic characterisation

The paper describes a measurement device for obtaining the kinematic characterisation and isometric loading of ankle joints under different working conditions. Non-invasive,in vivo experiments can be conducted with this experimental apparatus, the potential of which could be usefully exploited in basic biomedical research, prosthesis design, clinical applications, sports medicine and rehabilitation. The device determines the 3D movement of the foot with respect to the shank and evaluates the torques and moments around the three articular axes in relation to any desired angular position of the ankle complex. When integrated with superficial electromyographic techniques and electrical stimulation, it allows the assessment of the functionality of the lower leg in both mechanical and myo-electrical terms. The paper reports the main mechanical and electronic features of the device (high linearity; maximum moment ranges ±300 Nm for flexion-extension, ±35 Nm for both pronation-supination and internal-external rotation; angular ranges: ±100° of dorsi-plantar flexion, ±50° of internal-external rotation and prono-supination; linear ranges: ±25 mm along each axis). Results from a healthy volunteer, under voluntary or stimulated conditions, helped in testing its operatability, reliability, robustness, repeatability and effectiveness. Preliminary simplified protocols have been also applied to 20 healthy volunteers, and the main results were 80.8±11.9° of internal-external rotation, 46.2±9.1° of prono-supination and 74.6±13.1° of flexion-extension. Torques and moments were normalised with respect to a body mass index of 30. The maximum plantar flexion moment (57.5±21.3 Nm) was measured with the foot at 15° of dorsal flexion; the maximum dorsal flexion moment (50.2±20.3 Nm) was measured with the foot at 15° of plantar flexion.     

The role of active forces and intersegmental dynamics in the control of limb trajectory over obstacles during locomotion in humans

The focus of this paper is to examine the contributions of active and passive forces in the control of limb trajectory over obstacles during locomotion. Kintetic analyses of the swing phase of locomotion were carried out to determine the power profiles at various joints and to parcel the joint moments into moments due to muscle action, gravitational force and motion-dependent terms. The analyses revealed that toe elevation over the obstacles was achieved primarily by flexing at the hip, knee and ankle joint. Power analyses showed that translational energy applied at the hip joint and rotational energy applied at the knee joint were modulated as functions of obstacle height. This demonstrates that increased hip and ankle joint flexion are achieved not through active muscle action but rather through passive forces induced by translational action at the hip (representing contribution by the stance limb muscles) and rotational action at the knee joint. Parcelling the joint moment terms into various components clearly shows how the nervous system exploits intersegmental dynamics to simplify control of limb elevation over obstacles and minimize energy costs.     

In vivo muscle fibre behaviour during counter-movement exercise in humans reveals a significant role for tendon elasticity

Six men performed a single ankle plantar flexion exercise in the supine position with the maximal effort with counter movement (CM, plantar flexion preceded by dorsiflexion) and without counter movement (NoCM, plantar flexion only) produced by a sliding table that controlled applied load to the ankle (40 % of the maximal voluntary force). The reaction force at the foot and ankle joint angle were measured using a force plate and a goniometer, respectively. From real-time ultrasonography of the gastrocnemius medialis muscle during the movement, the fascicle length was determined. The estimated peak force, average power, and work at the Achilles' tendon during the plantar flexion phase in CM were significantly greater than those in NoCM. In CM, in the dorsiflexion phase, fascicle length initially increased with little electromyographic activity, then remained constant while the whole muscle-tendon unit lengthened, before decreasing in the final plantar flexion phase. In NoCM, fascicle length decreased throughout the movement and the fascicle length at the onset of movement was longer than that of the corresponding phase in CM. It was concluded that during CM muscle fibres optimally work almost isometrically, by leaving the task of storing and releasing elastic energy for enhancing exercise performance to the tendon.     

Effect of prior isometric muscle action on concentric torque output during plantar flexion

The influence of different levels of prior isometric muscle action on the concentric torque output during plantar flexion was examined at two angular velocities (60°·s^–1 and 120°·s^–1) in ten healthy female subjects. The levels of the prior muscle actions were 25%, 50%, 75% and 100% of the maximal voluntary isometric contraction (MVIC). A KINetic-COMmunicator II dynamometer was used to measure torque output during plantar flexion within a range of motion of 78°-120° of the ankle joint. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the gastrocnemius medialis muscle and the soleus muscle. Torque-angle curves were made for the plantar flexions using different prior muscle actions. Up to 75% of MVIC, the torque output in the first part of the range of motion increased with the level of the prior isometric muscle action; at higher levels of MVIC the torque did not appear to increase any further. Later in the range of motion, after 24° in the plantar flexion at a velocity of 60°·s^–1 and 31° at 120°·s^–1, the prior muscle actions had no further influence. No increase was found in the electromyograms, with one exception, during the concentric movements when preceded by higher levels of MVIC. It would seem therefore that the increase in torque output early in the range of motion cannot be explained on the basis of differences in electrical muscle activation in this study.     

Medial gastrocnemius muscle growth during adolescence is mediated by increased fascicle diameter rather than by longitudinal fascicle growth

Using a cross-sectional design, the purpose of this study was to determine how pennate gastrocnemius medialis (GM) muscle geometry changes as a function of adolescent age. Sixteen healthy adolescent males (aged 10–19 years) participated in this study. GM muscle geometry was measured within the mid-longitudinal plane obtained from a 3D voxel-array composed of transverse ultrasound images. Images were taken at footplate angles corresponding to standardised externally applied footplate moments (between 4 Nm plantar flexion and 6 Nm dorsal flexion). Muscle activity was recorded using surface electromyography (EMG), expressed as a percentage of maximal voluntary contraction (%MVC). To minimise the effects of muscle excitation, EMG inclusion criteria were set at < 10% of MVC. In practice, however, normalised EMG levels were much lower. For adolescent subjects with increasing ages, GM muscle (belly) length increased due to an increase in the length component of the physiological cross-sectional area measured within the mid-longitudinal plane. No difference was found between fascicles at different ages, but the aponeurosis length and pennation angle increased by 0.5 cm year⁻¹ and 0.5 ° per year, respectively. Footplate angles corresponding to externally applied 0 and 4 Nm plantarflexion moments were not associated with different adolescent ages. In contrast, footplate angles corresponding to externally applied 4 and 6 Nm dorsal flexion moments decreased by 10 ° between 10 and 19 years. In conclusion, we found that in adolescents'' pennate GM muscles, longitudinal muscle growth is mediated predominantly by increased muscle fascicle diameter.     

Contrasting roles of inertial and muscle moments at knee and ankle during paw-shake response

Intralimb kinetics of the paw-shake response (PSR) were studied in four spinal, adult cats. Using rigid body equations of motion to determine the dynamic interactions between limb segments, knee and ankle joint kinetics were calculated for the steady-state cycles as defined in the preceding paper. Hindlimb motion was filmed (200 frames/s) to obtain knee and ankle kinematics. Responses of flexors and extensors at both joints were recorded synchronously with cinefilm. Ankle and knee joint kinematics were determined from 51 steady-state cycles of 16 PSRs. Average maximum displacements, velocities, and accelerations were substantially greater for the ankle than for the knee joint. Knee and ankle motions were out of phase in the first part of the cycle; knee extension occurred simultaneously with ankle flexion. In the second part of the cycle, motions at the two joints were sequential; rapid knee flexion, accompanied by negligible ankle displacement, preceded rapid ankle extension with minimal knee displacement. At the ankle joint, peak net moments tending to cause flexion and extension were similar in magnitude and determined primarily by muscle moments. Moments due to leg angular acceleration contributed significantly to an extensor peak in the net moment near the end of the cycle. Other inertial and gravitational moments were small. At the knee joint, net moments tending to cause flexion and extension were also similar, but smaller than those at the ankle. The knee muscle moments, however, were large and counteracted large inertial moments due to paw angular acceleration. Also, moments due to leg angular acceleration and knee linear acceleration were substantial and opposite in effect. Other inertial and the gravitational moments were negligible. Muscle moments slowed and reversed joint motions, and active muscle force components of muscle moments were derived from lengthening of active musculotendinous units. Segmental interactions, in which proximal segment motion augmented distal segment velocity, increased the effectiveness of PSR steady-state cycles by facilitating the generation of extremely large paw linear accelerations. Limb oscillations during PSR steady-state result from interactions between muscle synergies and motion-dependent limb dynamics. At the ankle, muscle activity functioned to control paw acceleration, whereas at the knee, muscle activity functioned to control leg and paw inertial interactions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of growth on geometry of gastrocnemius muscle in children: a three-dimensional ultrasound analysis

During development, muscle growth is usually finely adapted to meet functional demands in daily activities. However, how muscle geometry changes in typically developing children and how these changes are related to functional and mechanical properties is largely unknown. In rodents, longitudinal growth of the pennate m. gastrocnemius medialis (GM) has been shown to occur mainly by an increase in physiological cross-sectional area and less by an increase in fibre length. Therefore, we aimed to: (i) determine how geometry of GM changes in healthy children between the ages of 5 and 12 years, (ii) test whether GM geometry in these children is affected by gender, (iii) compare normalized growth of GM geometry in children with that in rats at similar normalized ages, and (iv) investigate how GM geometry in children relates to range of motion of angular foot movement at a given moment. Thirty children (16 females, 14 males) participated in the study. Moment-angle data were collected over a range of angles by rotating the foot from plantar flexion to dorsal flexion at standardized moments. GM geometry in the mid-longitudinal plane was measured using three-dimensional ultrasound imaging. This geometry was compared with that of GM geometry in rats. During growth from 5 to 12 years of age, the mean neutral footplate angle (0 Nm) occurred at -5° (SD 7°) and was not a function of age. Measured at standardized moments (4 Nm), footplate angles towards plantar flexion and dorsal flexion decreased by 25 and 40%, respectively. In both rats and children, GM muscle length increased proportionally with tibia length. In children, the length component of the physiological cross-sectional area and fascicle length increased by 7 and 5% per year, respectively. Fascicle angle did not change over the age range measured. In children, the Achilles tendon length increased by 6% per year. GM geometry was not affected by gender. We conclude that, whereas the length of GM in rat develops mainly by an increase in physiological cross-sectional area of the muscle, GM in children develops by uniform scaling of the muscle. This effect is probably related to the smaller fascicle angle in human GM, which entails a smaller contribution of radial muscle growth to increased GM muscle length. The net effect of uniform scaling of GM muscle belly causes it to be stiffer, explaining the decrease in range of motion of angular foot movement at 4 Nm towards dorsal flexion during growth.     

Withdrawal reflex organisation to electrical stimulation of the dorsal foot in humans

The present study investigated excitatory reflex receptive fields for various muscle reflex responses and reflex mediated ankle joint movements using randomised electrical stimulation of the dorsal and plantar surface of the foot in 12 healthy subjects. Eleven electrodes (0.5-cm2 cathodes) were mounted on the dorsal side and three on the plantar side of the foot. A low (1.5 times pain threshold) and a high (2.3 times pain threshold) stimulus intensity were used to elicit the reflexes. EMG signals were recorded from tibialis anterior (TA), gastrocnemius medialis (GM), soleus (SO), biceps femoris (BF), and rectus femoris (RF) muscles together with the ankle movement measured by a goniometer. The withdrawal pattern evoked from the dorsal side consisted of two separate responses with different receptive fields: (1) early EMG responses in GM and BF (50-120 ms) evoking knee flexion, probably of purely spinal origin, and (2) a late response in GM and SO (120-200 ms) that may be under supraspinal control. The ankle flexor TA was significantly activated in both time windows, but in 11 of 12 subjects its contraction was too small to cause significant dorsal flexion. In the ankle joint inversion was the most dominant movement. Stimulation of the plantar side resulted in activation of TA when stimulating the forefoot and in activation of triceps surae when stimulating the heel. These observations show that painful stimuli activate appropriate muscles depending on stimulus location to initiate the adequate withdrawal. For proximal muscles (e.g. knee flexors) the receptive field covers almost the entire foot (dorsal and plantar sides) while more distal muscles have a smaller receptive field covering only a part of the foot. This adequate withdrawal movement suggests a more refined withdrawal reflex organisation than a stereotyped flexion of all joints to avoid tissue damage.     

Force-length characteristics of the in vivo human gastrocnemius muscle

In this study, the force-length characteristics of the in vivo medial (GM) and lateral (GL) heads of the human gastrocnemius muscle were estimated from measurements in eight healthy male subjects. This involved: 1) dynamometry-based measurements of the moment generated during maximal isometric plantar flexion; 2) ultrasound-based measurements of fascicular length and pennation angle; and 3) ultrasound-based calculations of moment arm lengths. All measurements were taken over the ankle angle range from 20 degrees of dorsiflexion to 30 degrees of plantar flexion. Tendon forces were calculated by dividing the moments recorded by the muscle moment arm lengths, and fascicular forces were calculated by dividing the tendon forces estimated by the cosine of pennation angle. In the transition from 30 degrees of plantar flexion to 20 degrees of dorsiflexion, the GM muscle fascicular length and force increased linearly from 24 to 39 mm and from 222 to 931 N, respectively. Over the same ankle angle range, the GL muscle fascicular length and force increased linearly from 30 to 47 mm and from 139 to 393 N, respectively. Estimates of the sarcomeric lengths corresponding to the fascicular lengths measured indicated that the two muscles operated in the range 1.4-2.2 microm, below the optimal length region for force generation according to the cross-bridge mechanism of contraction. These results indicate that the force-length relation of the in vivo human gastrocnemius muscle is limited to the ascending limb of the bell-shaped force-length curve obtained from experiments on isolated material.     

The innervation of the joints of the foot

The nerve supply of the ankle joint and of the joints of the foot was studied in dissections of fetal and adult feet and in serial sections of fetal feet stained with silver. The ankle joint was supplied by the tibial, sural, deep peroneal, and saphenous nerves, and by the accessory deep peroneal nerve when present. The tarsal joints were supplied on their plantar aspects by the medial or lateral plantar nerves, and on their dorsal aspects chiefly by the deep peroneal nerve. The joint between the lateral and intermediate cuneiform received branches from the intermediate dorsal cutaneous nerve also. The lateral dorsal cutaneous nerve and the accessory deep peroneal nerve when present provided additional branches to the subtalar and calcaneocuboid joints. The tarsometatarsal joints were supplied on their plantar aspects by the medial or lateral plantar nerves. Most of them were supplied on their dorsal aspects by the deep peroneal nerve, but the cuboid-metatarsal joints received their supply from the intermediate dorsal cutaneous nerve. The intermetatarsal joints had a similar but sparser supply. The joint between the fourth and fifth metatarsal received branches from the intermediate dorsal cutaneous nerve. The plantar digital nerves provided the main supply to the metatarsophalangeal joints. The dorsal aspect of the first metatarsophalangeal joint was supplied by the deep peroneal and the medial dorsal cutaneous nerves, of the second metatarsophalangeal joint by the deep peroneal nerve, and of the fourth and fifth metatarsophalangeal joints by the lateral dorsal cutaneous nerve. The interphalangeal joints did not receive articular branches from the dorsal digital nerves, except in the case of the interphalangeal joint of the big toe, which was supplied by the deep peroneal and the medial dorsal cutaneous nerves.     

基于统计参数映射分析跑鞋跟掌落差对下肢关节负荷的影响

目的 探讨在相同跑速下穿着不同落差跑鞋对下肢关节负荷的影响,为跑鞋设计和跑步者选购跑鞋提供依 据。 方法 18 名男性跑步者分别穿着零落差和 10 mm 落差跑鞋以(4. 0±0. 2) m/ s 速度完成测试,使用红外高速运 动捕捉系统和三维测力台同步采集下肢运动学参数和地面反作用力( ground reaction force, GRF)。 使用统计参数 映射法(statistical parameter mapping,SPM)分析跑鞋跟掌落差对支撑期垂直 GRF、下肢关节三维力矩的影响。 结 果 跑鞋跟掌落差对垂直 GRF 无影响,对下肢关节部分力矩-时间序列影响显著。 与穿着零落差跑鞋相比,穿着 10 mm 落差跑鞋在 27% ~ 38% 支撑期髋关节内旋力矩增加,在 47% ~ 75% 支撑期膝关节伸展力矩增加,在 16% ~ 33% 、25% ~ 30% 、12% ~ 25% 支撑期踝关节跖屈力矩、外翻力矩和外旋力矩降低。 结论 与穿着零落差跑鞋相比,穿 着 10 mm 落差跑鞋在支撑前期髋关节负荷增加,踝关节负荷降低,在支撑中期膝关节负荷增加。 建议跑步者结合 自身特点及跑鞋跟掌落差对下肢关节负荷特征的影响,选择适合自己的跑鞋。     

基于肌肉机械功的异常步态分析

目的通过量化背屈肌和跖屈肌之间的协同作用分析不同行走速度下偏瘫受试者踝关节角度的异常,以深层次地分析患者的运动功能。方法将从肌电(electromyograph,EMG)驱动的人体肌肉骨骼模型中获得的肌力、力臂和关节角度参数进行预处理,利用肌力和力臂差计算患侧跖屈肌群和背屈肌群做功情况,以此分析由踝关节角度曲线反映出的步态异常。结果跖屈肌群(主要是比目鱼肌和腓肠肌)过度活跃做正功,保持高强度向心收缩,背屈肌群(主要是胫骨前肌)无力几乎不做功导致肌肉协同失衡,从而引起步态异常。结论本文提出的量化肌肉机械功方法可以深层次地分析肌肉之间的协同作用,对于偏瘫患者异常步态的分析具有重要的意义。     

Analysis of Musculoskeletal Loadings in Lower Limbs During Stilts Walking in Occupational Activity

Construction workers often use stilts to raise them to a higher level above ground to perform many tasks, such as taping and sanding on the ceiling or upper half of a wall. Some epidemiological studies indicated that the use of stilts may place workers at increased risk for knee injuries or may increase the likelihood of trips and falls. In the present study, we developed an inverse dynamic model of stilts walking to investigate the effects of this activity on the joint moments and musculoskeletal loadings in the lower limbs. The stilts-walk model was developed using the commercial musculoskeletal simulation software AnyBody (version 3.0, Anybody Technology, Aalborg, Denmark). Simulations were performed using data collected from tests of four subjects. All subjects walked without or with stilts through a 12-m straight path. The moments of the knee, hip, and ankle joints, as well as forces in major muscles or muscle groups in the lower limbs, for stilts walking were compared with those for normal walking. Our simulations showed that the use of stilts may potentially increase the peak joint moment in knee extension by approximately 20%; induce 15% reduction and slight reduction in the peak joint moments in ankle plantar flexion and hip extension, respectively. The model predictions on the muscle forces indicated that the use of stilts may potentially increase loadings in five of eight major muscle groups in the lower extremities. The most remarkable was the force in rectus femoris muscle, which was found to potentially increase by up to 1.79 times for the stilts walking compared to that for the normal walking. The proposed model would be useful for the engineers in their efforts to improve the stilts design to reduce musculoskeletal loadings and fall risk.     

经皮锁定加压钢板固定胫骨多段骨折21例疗效分析

目的探讨经皮锁定加压钢板(locking compression plate,LCP)手术治疗胫骨多段骨折的临床疗效。方法将2010年6月~2011年12月收治的胫骨多段骨折患者,根据AO分类方法筛选出C2型骨折21例:左侧9例,右侧12例;男性14例,女性7例;年龄15~71岁,平均(44±2.1)岁。入选病例均采用微创经皮插入LCP钢板手术内固定治疗。结果随访8~15个月,术后3~4月骨折线变模糊,术后6~9月骨折处出现大量骨痂;膝关节屈曲为(147±3.2)°,伸直为(0±0.5)°;踝关节背伸(9±1.2)°,跖屈(43±2.1)°;Johner-Wruhs评分标准:优17例,良3例,可1例,差0例;优良率95.24%。结论经皮LCP钢板固定胫骨多段骨折安全、有效,是值得推广的手术方式。     

A Population of Patient-Specific Adult Acquired Flatfoot Deformity Models Before and After Surgery

Following IRB approval, a cohort of 3-D rigid-body computational models was created from submillimeter MRIs of clinically diagnosed Adult Acquired Flatfoot Deformity patients and employed to investigate postoperative foot/ankle function and surgical effect during single-leg stance. Models were constrained through physiologic joint contact, passive soft-tissue tension, active muscle force, full body weight, and without idealized joints. Models were validated against patient-matched controls using clinically utilized radiographic angle and distance measures and plantar force distributions in the medial forefoot, lateral forefoot, and hindfoot. Each model further predicted changes in strain for the spring ligament, deltoid ligament, and plantar fascia, as well as joint contact loads for three midfoot joints, the talonavicular, navicular-1st cuneiform, and calcaneocuboid. Radiographic agreement ranged across measures, with average absolute deviations of <5° and <4 mm indicating generally good agreement. Postoperative plantar force loading in patients and models was reduced for the medial forefoot and hindfoot concomitant with increases in the lateral forefoot. Model predicted reductions in medial soft-tissue strain and increases in lateral joint contact load were consistent with in vitro observations and elucidate the biomechanical mechanisms of repair. Thus, validated rigid-body models offer promise for the investigation of foot/ankle kinematics and biomechanical behaviors that are difficult to measure in vivo.     

2~5掌指关节屈伸活动中关节面应力分布的有限元分析

目的　建立掌指关节三维有限元模型,分析掌指关节屈伸活动中掌指关节面应力分布情况。 方法　健康男性志愿者1名,对其右手掌指关节分别于0°、30°、60°、90°屈曲位进行CT扫描,利用扫描数据建立掌指关节三维有限元模型;于4个角度沿指骨径向分别施以10、20、30、40、50 N荷载,观察掌指关节应力分布,并对结果进行分析。 结果　4组不同弯曲角度的掌指关节网格模型节点数量、单元数量基本相同,每组模型约40070个节点,178903个四面体单元。相同载荷作用下,弯曲的角度越大,各掌指关节面的应力越大。在实现0°、30°、60°、90°屈曲过程中,2~5掌指关节掌骨头应力峰值变化范围分别为0.20~2.46、0.22~1.58、0.22~1.69、0.22~2.25 Mpa。 结论　掌指关节屈伸过程中,弯曲的角度越大,掌指关节面的接触应力越大,其应力分布范围亦增大。     

成人踝关节关节面的应用解剖学观测

目的观测成人踝关节的相关形态学指标,为踝关节损伤修复、关节置换等提供解剖学依据,同时积累国人人体解剖学资料。方法利用游标卡尺、量角器、求积仪等,对53具成人骨骼的完整踝关节进行形态学测量。结果踝关节面积：腓骨踝关节面面积（3．70±0．41）cm2,胫骨踝关节面面积（2．50±1．56）cm2,距骨滑车面积（10．60±1．87）cm2,距骨内踝关节面面积（2．20±1．86）cm2、外踝关节面面积（3．30±0．61）cm2。距骨滑车测量：距骨滑车关节凹深度（0．30±0．18）cm;内、外侧唇的高度分别为（0．50±0．21）am、（0．90±0．12）cm;前缘宽度（2．70±0．33）cm;后缘宽度（2．00±0．58）cm。踝关节各面间以及与下肢轴线的交角：内、外踝关节面与距骨滑车平面交角分别为（109．00°±1．58°）、（116．00°±1．21°）;内、外踝关节面与下肢轴线交角分别为（18．00°±1．08°）、（26．00°±1．36°）。结论踝关节损伤修复、关节置换等均应以踝关节的形态学参数为依据方能达到良好的疗效。     

The effect of muscle length on motor-unit recruitment during isometric plantar flexion in humans

The triceps surae muscle group, consisting of the mono-articular soleus (SOL) and bi-articular gastrocnemius (GAS) muscles, primarily generates plantar flexor torque. Since the GAS muscle crosses the knee joint, flexion of the knee reduces the length of this muscle, thus limiting its contribution to torque output. However, it is not clearly understood how the central nervous system activates muscles that are at inefficient or non-optimal force-producing lengths. Therefore, the present study was designed to determine the effect of muscle length on motor-unit recruitment in the medial GAS muscle. Single motor-unit activity was recorded from the medial GAS muscle while electromyographic (EMG) activity was recorded from the SOL muscle in nine male subjects. With the ankle angle held constant at 90 degrees, the knee angle was changed from 180 degrees to 90 degrees, corresponding to a long and short GAS muscle length, respectively. Levels of voluntary plantar flexor torque were produced at a rate of 2 Nm.s-1 until motor-unit activity was detected. A total of 229 motor units were recorded, of which 121 and 108 were obtained at the long and short muscle lengths, respectively. At the short length, onset of motor-unit activity occurred at significantly higher levels of plantar flexor torque and SOL EMG. Onset of motor-unit activity occurred at 2.97 +/- 7.78 Nm and 32.14 +/- 10.25 Nm, corresponding to 0.045 +/- 0.075 mV and 0.231 +/- 0.129 mV of SOL EMG in the long and short positions, respectively. No individual GAS motor unit could be recorded at both muscle lengths. Motor units in the shortened GAS muscle may be influenced by peripheral afferents capable of reducing the excitability of the motoneurone pool. This may also reflect a specific inhibition of motor units having shortened, non-optimal fascicle lengths, and they are thereby incapable of contributing to plantar flexor torque.     

Relation between electromyogram and torque of isometric reflex contractions in man

Human subjects maintained isometric plantar or dorsal flexions of the ankle in a matching task. H-reflexes of different sizes were superimposed on the steady activity. The peak-to-peak amplitude of the reflexes was measured on the electromyogram (EMG) of the soleus muscle. The size of the corresponding muscle contractions was determined on the isometric torque signal in relation to the maintained flexion force. The EMG-torque relation which was defined as the reflex muscle contraction as a function of the EMG reflex signal approximated a square root function for a given steady contraction level. It was not modulated by steady dorsal flexions, but it decreased continuously with stronger plantar steady torques. This dependence was caused by the silent period following the reflex discharge. Since the reflex discharge and the silent period were near in time to the duration of the contraction, the silent period had a direct effect on the reflex contraction amplitude.     

Angle dependency in strength measurements of the ankle plantar flexors

Summary Muscle strength (or muscular moment) generated during dynamic contractions varies with joint angle. This raises the question about the choice of a representative angle in the evaluation of strength capacity. To assess this angle dependency in strength measurements, dynamic moment-angle curves for plantar flexor muscles were obtained in 43 healthy subjects (28 men and 15 women) with a controlled acceleration dynamometer at 0.52 rad s^–1 (30° s^–1) and using maximal static preloading before the beginning of movement to attenuate the force development phase. Differences between gender and correlations between strength and anthropometric measures were calculated at each 0.087 rad (5°). The plantar flexion moment was larger in men, in general, but this difference was largest when the ankle was most dorsiflexed. The correlations between moment and anthropometric measures were also higher in the first half of the plantar flexion movement. These results stress the importance of reporting joint angles at which moment of force measures were made. Furthermore, they show that the maximal strength capacity of the plantar flexors is best represented by the moment measured in dorsiflexion angles when the muscles are lengthened.