Erratum to: Load-dependent movement regulation of lateral stretch shortening cycle jumps

The classical stretch shortening cycle (SSC) describes sagittal joint flexion–extensions in motions like running or hopping. However, lateral movements are integral components of team sports and are associated with frontal plane joint displacements. The purpose of this study is to identify neuromuscular and kinematical mechanisms determining motor control and performance of reactive laterally conducted SSCs. Lateral jumps were performed from four distances in order to investigate the influence of lateral stretch loads on the lower extremity. Electromyographic (EMG) data of nine lower extremity muscles were collected. Foot, ankle, knee, and hip kinematics were recorded by 3-D motion analysis. High stretch loads were characterized by a greater foot exorotation during the initial phase of contact. In the sagittal plane knee and hip joint, displacements increased, whereas in the frontal plane only the hip joint displacement was significantly raised. In particular, frontal peak joint moments increased with stretch load. Thigh muscles’ mean pre-activity amplitude was enhanced. It was possible to detect stretch reflexes in the thigh muscles, whereas in particular the short-latency reflex (SLR) was stretch load-dependently modulated. The results of the present study suggest that the foot exorotation seems to play a decisive role in the movement control of lateral jumps. The association between exorotation and increased sagittal joint displacements may be seen as a compensation strategy to shift load from the frontal to the sagittal plane. Lateral load compensation seems to strongly depend on upper leg’s kinematic and neuromuscular adjustments, rather than on the ankle joint complex.     

Task-specific initial impact phase adjustments in lateral jumps and lateral landings

Load-dependant adjustments in lateral jumps are thought to rely on foot placement and on upper leg’s kinematic and neuromuscular adaptations. The aim of this study was to elucidate task-specific adjustments during the initial impact phase under varying stretch-loads by the comparison of lateral jumps and lateral landings. Ten subjects performed lateral jumps and landings from four distances. Electromyographic (EMG) data of five lower extremity muscles were measured, whilst lower extremity kinematics and kinetics were analysed by 3D motion analysis. Lateral jumps were characterized by increased impact forces, higher lower extremity joint moments with exception of the initial knee abduction moment, greater sagittal knee and hip joint displacements, and a further exorotated foot placement. In lateral landings frontal ankle and hip joint displacements were greater. Thigh muscle and m. tibialis anterior (TA) pre-activity as well as initial post-impact EMG were higher in lateral jumps than in lateral landings, whilst during the reflex-induced phase thigh and shank muscle EMG, except for TA, were enhanced in lateral jumps. From these findings it can be concluded that task specificity in lateral jumps in contrast to lateral landings impedes a stretch-load adequate modulation of initial impact forces which particularly affects ankle joint loading. Foot placement seems to play a decisive role for limiting lateral ankle and medial knee joint loading. Therefore, in sports containing high-impact frontal plane movements a special emphasis in training routines should be paid to foot placement strategy in those movements. Such training interventions might contribute to injury prevention in lateral movements.     

Role of intramuscular receptors in the awareness of limb position

We studied proprioception with the ankle joint and the metacarpophalangeal (MCP) joint of the index finger of humans by use of a method that could distinguish a position sense from a movement sense. The test measured how subjects' ability to detect a fixed displacement of a joint varied with the rate of joint rotation. A position sense should not depend on the speed of joint placement; therefore slow rates of movement should not degrade subjects' ability to sense joint displacements. However, in the absence of a position sense, subjects would presumably rely on movement signals that do depend on the rate of rotation, and their ability to detect displacements should decrease when rate decreases. Subjects could sense small displacements of the ankle (+/- 3.5 degrees) and the MCP joint (+/- 2.5 degrees lateral excursions) with no decrement in performance at speeds as low as 0.25 degrees/min for the ankle and 0.5 degrees/min for the MCP joint (the slowest tested thus far). The findings confirm the existence of a position sense with these joints. Block of the ulnar nerve at the wrist, which paralyzes the interosseous muscles that adduct and abduct the MCP joint but presumably leaves skin and joint mechanisms unaffected, substantially impaired subjects' ability to detect the lateral excursions at slow speeds. Performance fell sharply at speeds less than 128 degrees/min and leveled off at approximately 20% detections at speeds less than 4 degrees/min. Increasing displacement to +/- 7 degrees did not improve performance. Block of the common peroneal nerve at the knee, which paralyzes the ankle dorsiflexor muscles, substantially impaired subjects' ability to detect the +/- 3.5 degrees displacements at slow speeds when the foot was positioned to slacken the plantarflexion muscles (which were not affected by the block). Performance fell sharply at speeds less than 256 degrees/min and approached zero at speeds less than 16 degrees/min. However, positioning the foot to stretch the plantarflexor muscles restored subjects' performance to near normal. Local anesthetic injected into the MCP joint space produced no observable effect on the ability to detect either slow or fast excursions. The joint anesthesia went unnoticed by the subject. We conclude that independent and separable senses exist for limb position and limb movement and that normal position sense requires sensory inputs from the muscles.     

Software for determining lower extremity muscle-tendon kinematics and moment arm lengths during flexion/extension movements.

A computer program was developed to calculate lower extremity muscle-tendon (MT) kinematics and flexion/extension moment arm (MA) lengths for any subject performing movements constrained to occur in the sagittal plane. The program requires as input subject anthropometric and time series ankle, knee, and hip angle data. Using these data a lower extremity link-segment model is constructed for each time element. Muscle-tendon attachment data and a straight line muscle model are used to calculate MT and flexion/extension moment arm lengths. A finite difference technique is used to determine MT shortening velocity. The utility of this program is demonstrated by calculating MT kinematics and MA lengths for six muscles of a single subject both as a function of joint angles and during gait.     

髋外展肌疲劳对不同性别人群单腿侧跳落地时神经肌肉控制的影响

目的 比较髋外展肌疲劳对不同性别人群单腿侧跳落地期间的姿势稳定性及其神经肌肉控制的影响。方法 比较20名男性和20名女性在髋外展肌疲劳干预前后进行单腿侧跳落地期间的压力中心(center of pressure, COP)、地面反作用力(ground reaction force, GRF)、下肢运动学、关节力矩、肌肉活动度等。结果 疲劳后,男性和女性COP在冠状面的最大位移和平均速度增加,髋关节外展峰值角度和踝关节外翻峰值角度增加,踝关节内翻峰值力矩增加。触地前200 ms,男性股直肌、股二头肌、胫前肌、腓骨长肌的激活小于女性;触地后200 ms,男性股二头肌激活小于女性。结论 髋外展肌疲劳导致冠状面姿势稳定性下降,髋、踝关节冠状面稳定性下降,可能增加关节损伤风险。不同性别人群的姿势调控策略存在差异,提示下肢关节损伤机制的性别差异值得进一步探究。     

慢跑的速度对青年女性下肢关节及肌肉的影响

目的 探讨合理的慢跑速度对体形和步姿的影响,使人在慢跑健身的同时兼得柔美的体态。方法 根据相关测量选择5种慢跑速度。利用运动捕捉系统采集研究对象(15位青年女性志愿者)在慢跑速度下的运动学数据,同时对下肢8块主要肌肉的肌电信号进行采集。计算获得在不同慢跑速度下髋、膝及踝关节矢状面的关节角度变化的均值。选择数据最接近均值的对象作为研究对象并进行运动学分析。结果 计算获得了该研究对象在不同慢跑速度下髋、膝及踝关节矢状面的关节角度以及下肢8块主要肌肉的激活度曲线。运用打分的方法,本文给出了研究对象慢跑速度、慢跑阶段、肌肉激活度与关节角度之间的关系。结论 各关节角的变化范围和各肌肉最大激活度并不随慢跑速度的变化而单调变化。本文为青年女性健身时选择适合自己的慢跑速度提供了参考。     

Biomechanical effects of body weight support with a novel robotic walker for over-ground gait rehabilitation

Body weight support (BWS) promotes better functional outcomes for neurologically challenged patients. Despite the established effectiveness of BWS in gait rehabilitation, the findings on biomechanical effects of BWS training still remain contradictory. Therefore, the aim of this study is to comprehensively investigate the effects of BWS. Using a newly developed robotic walker which can facilitate pelvic motions with an active BWS unit, we compared gait parameters of ten healthy subjects during a 10-m walk with incremental levels of body weight unloading, ranging from 0 to 40 % at 10 % intervals. Significant changes in joint angles and gait temporospatial parameters were observed. In addition, the results of an EMG signal study showed that the intensity of muscle activation was significantly reduced with increasing BWS levels. The reduction was found at the ankle, knee, and hip joints in the sagittal plane as well as at the hip joint in the frontal plane. The results of this study provide an important indication of increased lateral body balance and greater stabilization in sagittal and frontal plane during gait. Our findings provide a better understanding of the biomechanical effects of BWS during gait, which will help guide the gait rehabilitation strategies.     

Effects of severity of degeneration on gait patterns in patients with medial knee osteoarthritis

This study tested the hypothesis that patients with mild and severe medial knee osteoarthritis (OA) adopt different compensatory gait patterns to unload the deseased knee, in not only the frontal plane but also the sagittal plane. Fifteen patients with mild and 15 with severe bilateral medial knee OA, and 15 normal controls walked while the kinematic and kinetic data were measured. Compared to the normal group, both OA groups had significantly greater pelvic anterior tilt, swing-pelvis list, smaller standing knee abduction, as well as smaller standing hip flexor and knee extensor moments during stance. The severe group also had greater hip abduction, knee extension and ankle plantarflexion. The mild group successfully reduced the extensor moment and maintained normal abductor moment at the diseased knee mainly through listing and anterior tilting the pelvis. With extra compensatory changes at other joints and increased hip abductor moment, the severe group successfully reduced the knee extensor moment but failed to reduce the abductor moment. These results suggest that, apart from training of the knee muscles, training of the hip muscles and pelvic control are essential in the rehabilitative intervention of patients with knee OA, especially for more severe patients.     

Effect of the hip motion on the body kinematics in the sagittal plane during human quiet standing

Human quiet stance is often modeled as a single-link inverted pendulum pivoting only around the ankle joints in the sagittal plane. However, several recent studies have shown that movement around the hip joint cannot be negligible, and the body behaves like a double-link inverted pendulum. The purpose of this study was to examine how the hip motion affects the body kinematics in the sagittal plane during quiet standing. Ten healthy subjects were requested to keep a quiet stance for 30 s on a force platform. The angular displacements of the ankle and hip joints were measured using two highly sensitive CCD laser sensors. By taking the second derivative of the angular displacements, the angular accelerations of both joints were obtained. As for the angular displacements, there was no clear correlation between the ankle and hip joints. On the other hand, the angular accelerations of both joints were found to be modulated in a consistent anti-phase pattern. Then we estimated the anterior–posterior (A–P) acceleration of the center of mass (CoM) as a linear summation of the angular acceleration data. Simultaneously, we derived the actual CoM acceleration by dividing A–P share force by body mass. When we estimated CoM acceleration using only the angular acceleration of the ankle joint under the assumption that movement of the CoM is merely a scaled reflection of the motion of the ankle, it was largely overestimated as compared to the actual CoM acceleration. Whereas, when we take the angular acceleration of the hip joint into the calculation, it showed good coincidence with the actual CoM acceleration. These results indicate that the movement around the hip joint has a substantial effect on the body kinematics in the sagittal plane even during quiet standing.     

坡面步行中青年女性下肢关节角及肌肉激活度

目的通过定量分析关节角及主要肌肉激活度的变化来说明步行速度和路面坡度对下肢运动的影响。方法首先按由慢到快选择了共5种步行速度,由低到高选择3种坡度,并利用运动捕捉系统对15各青年女性的步态进行测量,同时对影响下肢运动的8块主要肌肉的肌电信号进行了采集。然后通过计算分析获得她们在不同步行速度和路面坡度下髋、膝及踝关节矢状面的关节角度变化的均值,从测量数据中寻找出一个最接近这个均值曲线的研究对象。结果计算获得了该研究对象不同步行速度和路面坡度下踝关节、膝关节及髋关节在一个步态周期内的矢状面关节角的变化曲线以及主要肌肉的激活度变化曲线。结论每个步态周期内,关节角及肌肉激活度在5种不同速度下的变化很小;而在3种不同路面坡度下的变化仅趋势基本一致,峰值的差异却非常明显。     

Females with knee osteoarthritis use a detrimental knee loading strategy when squatting

BackgroundThe purpose of this study was to identify sex differences in lower limb kinematics, kinetics, and muscle activation patterns between individuals with osteoarthritis and healthy controls during a two-legged squat.MethodThirty OA (15 females) and 30 healthy (15 females) participants performed three 2-legged squats. Sagittal and frontal plane hip, knee, and ankle kinematics and kinetics were calculated. Two-way ANOVAs (Sex X OA Status) were used to characterize differences in squatting strategies between sexes and between those with and without knee OA.ResultsA greater decrease in sagittal hip, knee, and ankle range of motion and knee joint power was observed in the OA participants compared to the healthy controls. Females with OA had significantly reduced hip and knee adduction angles compared to the healthy females and males with OA. Females also had decreased hip power, hip flexion, and hip adduction moments and knee adduction moments compared to their male counterparts, with the greatest deficits observed in the females with OA. Females with OA also had the highest magnitude of muscle activation for the quadriceps, hamstrings, and gastrocnemius throughout the squat, while males with OA showed increased activation of the vastus lateralis and medial gastrocnemius compared to the healthy males.ConclusionsOA significantly altered biomechanics and neuromuscular control during the squat, with males employing a hip-dominant strategy, allowing them to achieve a greater lower limb range of motion.     

Kinematic alterations of the lower limbs and pelvis during an ascending stairs task are associated with the degree of knee osteoarthritis severity

Background

Individuals with knee osteoarthritis (OA) generally demonstrate great difficulty in ascending stairs. The strategies and compensations used by these individuals in stair activities have not been fully established. The purpose of this study was to investigate the joint kinematics of the pelvis, hip, knee and ankle throughout the gait cycle, in the sagittal and frontal planes, in individuals with mild and moderate knee OA, during an ascending stairs task.

Sex Differences in 2-DOF Human Ankle Stiffness in Relaxed and Contracted Muscles

Ankle stiffness has been known as one of the most important components contributing to the maintenance of lower body stability during postural balance and locomotion. It has been repeatedly shown that women have lower stability and increased risk of injury when compared to men participating in similar sports activities, yet sex differences in neuromuscular control of the ankle, including the modulation of ankle stiffness, and their contribution to stability remain unknown. To identify sex differences in human ankle stiffness, this study quantified multi-dimensional ankle stiffness in 20 young, healthy men and 20 young, healthy women over a range of ankle muscle contractions, from relaxed to 20% of maximum voluntary co-contraction of ankle muscles. A wearable ankle robot and a system identification method were used to reliably quantify ankle stiffness in a 2-dimensional space spanning the sagittal plane and the frontal plane. In all muscle activation levels, significant sex differences in ankle stiffness were identified in both the sagittal and frontal planes. In the given experimental conditions, ankle stiffness in males was higher than females up to 15.1 and 8.3 Nm/rad in the sagittal plane and the frontal plane, respectively. In addition, sex differences in the spatial structure of ankle stiffness were investigated by quantifying three parameters defining the stiffness ellipse of the ankle: area, aspect ratio, and orientation. In all muscle activation levels, a significant sex difference was identified in the area of stiffness ellipse as expected from the sex difference in the sagittal and frontal planes. However, no statistical sex difference was observed in the aspect ratio and orientation, which would be due to little differences in major anatomical configurations of the ankle joint between sexes. This study, in combination with future studies investigating sex differences during dynamic tasks (e.g. postural balance and locomotion) would serve as a basis to develop a risk assessment tool and sex-specific training programs for efficient ankle injury prevention or rehabilitation.     

Relative contribution of ankle and hip muscles in regulation of the human orthograde posture in a frontal plane

It was investigated, whether the postural regulation in the frontal plane takes place mainly at the hip or at the ankle level. The elimination of ankle torque was achieved by providing a point support in the frontal plane. (Two boards were attached to subject feet, below each board a metal pipe 2 cm diameter was fixed, so, the subject stood on contrivances resembling ‘skates’). The lateral displacements of breast and hip, the angle of ‘skates’ tilt and the characteristics of frontal stabilogram and electromyogram of two ankle muscles (m. peroneus and m. soleus) were compared in two situations: (1) during normal standing; (2) under the conditions of the exclusion of ankle torque from postural control. During normal standing the body behaved as two-link inverted pendulum. Transition from normal standing to standing on free ‘skates’ produced changes in the kinematics of body movement. Under the conditions of ankle torque exclusion (free ‘skates’) breast and hip of a subject moved in a frontal plane as a single unit (one-link inverted pendulum). During standing on free ‘skates’ the electromyographic activity of m. peroneus and m. soleus was the same as during normal standing (approximately 70–100 μV).     

Motor patterns of a fast voluntary postural task in man: trunk extension in standing

The co-ordination between muscles controlling the primary movement and associated postural adjustments during fast trunk extension movements was studied in six male subjects. Myoelectrical activity (EMG) was recorded from antagonistic muscle pairs at the trunk, hip, knee and ankle. Horizontal displacements of the upper trunk, hip and knee were recorded with an opto-electronic system (Selspot). A backward displacement of the trunk was accompanied by a forward displacement of the hip and knee. In general, the trunk started to move 30 ms before the hip and knee. Muscle activity first appeared in the ankle extensors (soleus/gastrocnemius) up to 150 ms prior to onset of prime mover muscles (trunk extensor, erector spinae; and hip extensors/knee flexors, hamstrings). This pre-activation was seldom followed by any detectable ankle joint movement. Prime mover muscles were activated simultaneously followed by the hip extensor gluteus maximus. Time to activation of muscles braking the movement (rectus abdominis, rectus femoris and vastus lateralis) was correlated with the amplitude of the primary movement (r = 0.63 0.75, P less than 0.01). Onset of activity in vastus lateralis was highly correlated with the amplitude of the forward displacement of the knee (r = 0.93, P less than 0.01). An associated postural adjustment appeared as an ankle flexion accompanied by activity in the ankle flexor tibialis anterior, and often also in the ankle extensors. This co-activation of antagonistic ankle muscles can under certain conditions have interesting functional implications for the control of posture.     

Neuromuscular functioning of athletes and non-athletes in the drop jump

In many sports vertical jumping is important. This study compared neuromuscular functioning of the lower extremity muscles together with some kinetic and kinematic parameters before and during ground contact in drop jumps from two heights [0.4?m (DJ40) and 0.8?m (DJ80)] in 7 highly trained triple-jumpers and 11 physically active controls. The triple-jumpers jumped 32% higher in DJ40 and 34% higher in DJ80, had shorter braking and total contact times, and greater average and peak vertical ground reaction forces than the controls. In both drop jumps in the electromyogram pre-activity of the vastus lateralis and gastrocnemius muscles started earlier in the jumpers than in the controls. For the control group the increase in dropping height was associated with a decrease in the propulsion force, and resulted in more extended knee and ankle angles at touch down and more flexed angles at the deepest position than for the jumpers. All angular displacements for DJ80 were larger than for DJ40 in the control group. The triple jumpers and control subjects differed with respect to their neuromuscular functioning in the drop jump exercise and they responded in a different way to the increase in dropping height.     

Modulation of lower limb withdrawal reflexes during gait: a topographical study

The aim of this study was to investigate the modulation and topography of the nociceptive withdrawal reflex elicited by painful electrical stimulation of the foot sole during gait. Fifteen healthy volunteers participated in this study. Cutaneous electrical stimulation was delivered on five locations of the foot sole after heel-contact, during foot-flat, after heel-off, and during the mid-swing phase of the gait cycle during treadmill walking. Reflexes were recorded from muscles of the ipsilateral and contralateral legs. Furthermore, the kinematic responses in the sagittal plane of the ipsilateral ankle, knee, and hip joints were recorded. Reflexes in the distal muscles showed a site-dependent modulation. The largest responses in tibialis anterior were evoked at the arch of the foot and the smallest at the heel (P < 0.05). The largest soleus responses were also elicited at the arch of the foot (P < 0.04). The EMG responses in flexors and extensors of the knee and extensors of the contralateral leg were generally not dependent on the stimulation site. The response at the three joints showed site dependency, especially during the swing phase where maximal flexion was obtained by stimulation at the arch of the foot (P < 0.05). The withdrawal reflex was modulated during the gait cycle and presented distinctive characteristics for the different muscles studied. Minimal kinematic responses were observed during stance in contrast to swing phase. Modulation of the reflex probably ensures an appropriate withdrawal but primarily secures balance and continuity of movement.     

Mechanical muscular power output and work during ergometer cycling at different work loads and speeds

Summary The aim of the study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling at different work loads and speeds. Six healthy subjects pedalled a weight-braked cycle ergometer at 0, 120 and 240 W at a constant speed of 60 rpm. The subjects also pedalled at 40, 60, 80 and 100 rpm against the same resistance, giving power outputs of 80, 120, 160 and 200 W respectively. The subjects were filmed with a cine-film camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work for the hip, knee and ankle joint muscles was calculated using a model based upon dynamic mechanics and described elsewhere. The total work during one pedal revolution significantly increased with increased work load but did not increase with increased pedalling rate at the same braking force. The relative proportions of total positive work at the hip, knee and ankle joints were also calculated. Hip and ankle extension work proportionally decreased with increased work load. Pedalling rate did not change the relative proportion of total work at the different joints.     

Intralimb coordination of the paw-shake response: a novel mixed synergy

Intralimb coordination of the paw-shake response (PSR) was studied in five normal and eleven spinal adult cats. Representative extensor and flexor muscles that function at the hip, knee, and ankle joints were recorded, and in six spinal cats the kinematics of these joints were determined from high-speed cinefilm. The PSR was characterized uniquely by mixed (flexor-extensor) synergies. Knee extensor (VL) and ankle flexor (TA) coactivity constituted one synergy, while the second synergy included hip extensors (GM, BF), knee flexors (BF, LG), and ankle extensor (LG). Joint displacements reflected the mixed synergy. Motions at the knee and ankle were out of phase, while motions at the hip were in phase with movements of the knee. Electromyographic burst durations and onset latencies were similar for normal and spinal cats, and in all cycles of a given PSR, the recruitment pattern was consistent for all muscles, except VL. High variability and missing bursts marked the activity of VL in some spinal cats. In PSRs with missing VL bursts, oscillations at the knee joint were not coordinated with cyclic actions at the hip and ankle. From the kinematic records three distinct phases of the PSR were identified: start-up consisted of the initial four to six cycles during which hip, knee, and ankle actions progressively became organized; steady-state included the middle three to five cycles that were characterized by consistent displacement at all three joints; and slow-down comprised the last three to four cycles during which the rate of oscillations slowed, and joint excursions decreased. During steady-state cycles, muscle contractions acted to reverse joint motions at the knee and ankle joints. Thus, knee and ankle extensor recruitment coincided with joint flexion, while joint flexors were recruited during joint extension. Muscle activity at the hip, however, was in phase with displacement. While neural input to muscle is consistent throughout the three phases of the PSR, segment motions can become progressively organized during start-up to achieve stable oscillations. Whether the PSR attains steady-state or not may hinge on the sensitive interplay that occurs between muscle activities and intersegmental mechanical interactions. That kinetic interplay is detailed in the following paper.     

搂膝拗步膝踝关节预激活与共收缩的表面肌电分析

目的 分析长期太极拳练习者进行搂膝拗步和正常行走时下肢膝、踝关节肌群预激活与共收缩的表面肌电（surface electromyography, sEMG）特征,探讨太极预防跌倒的神经肌肉控制策略。方法 采用Vicon运动捕捉系统、Kistler测力板和Noraxon表面肌电图系统同步采集搂膝拗步和正常行走时股直肌、股二头肌、胫骨前肌、外侧腓肠肌的sEMG信号和体位信息。通过股直肌和股二头肌、胫骨前肌和外侧腓肠肌两对肌肉的积分肌电分别计算膝、踝关节预激活和共收缩。结果 与正常行走相比,搂膝拗步在4个阶段的平均用时显著增加;搂膝拗步在4个阶段内时间百分比存在显著性差异;搂膝拗步膝关节共收缩水平和预激活水平降低,踝关节共收缩水平和预激活水平升高。结论 长期的太极拳练习可能使膝关节周围肌肉的激活水平提高,增强肌肉群之间的协同作用,以帮助稳定关节。研究结果为神经肌肉控制障碍疾病的康复评估和训练提供参考。