Assessment of tibial stiffness by vibration testing in situ--II. Influence of soft tissues, joints and fibula

The influence of soft tissues and joints on the vibration of the human tibia was examined by modal analysis on amputated lower limbs, where the soft tissues and the fibula were dissected gradually. Measurements were made in two different set ups, IFR and BRA, which were both designed to monitor fracture healing. In IFR, vibrations are generated by hammer impact on a relaxed hanging lower leg, with the knee flexed. Resonant frequencies are determined by a computer Fourier transform procedure. In BRA, a steady state vibration is induced in a lower leg, supported near the ankle and the tibial tuberosity, using an electromagnetic shaker. Resonant frequencies are determined from the maxima in vibration amplitudes. In both set ups the soft tissues have a similar influence on the vibration of the tibia: the skin hardly influences the determined modal parameter. The mass of the muscles influences both the resonant frequency and the damping. The fibula has a stiffening effect on the tibia. The influence of the joints is small in the IFR-set up: the tibia vibrates in conditions close to those for the free-free vibration. In the BRA-set up, the supports determine the boundary conditions.     

Deterioration of bone quality in the tibia and fibula in growing mice during skeletal unloading: gender-related differences

Skeletal unloading causes bone loss in both men and women; however, only a few studies have been performed on the effects of gender differences on bone quality during skeletal unloading. Moreover, although the fibula also plays an important role in load bearing and ankle stability, the effects of unloading on the fibula have been rarely investigated. The present study aimed to investigate the effects of skeletal unloading on bone quality of the tibia and fibula in growing animals and to determine whether differences existed between genders. Six-week-old female and male mice were randomly allocated into two groups. The right hindlimb of each mouse in the skeletal unloading group was subjected to sciatic neurectomy. After two weeks of skeletal unloading, the structural characteristics of the tibia and fibula in both genders were worsened. In addition, the bone mineralization density distribution (MDD) of the tibia and fibula in both genders were altered. However, the magnitude of deterioration and alteration of the MDD in the bones of females were larger than in those of males. These results demonstrate that skeletal unloading diminishes bone quality in the tibia and fibula, leading to an increase in bone fracture risks, particularly in females.     

Changes of bone morphology in response to hindlimb suspension of rats.

Effects of chronic hindlimb suspension or exposure to 2-G from postnatal day 4 to month 3 followed by ambulation recovery on the floor on the morphology of hindlimb bones were investigated in rats. The dorsi-flexion of the ankle was inhibited in the suspended group and such phenomena were not recovered at all. The mean weight and length of femur, tibia, and fibula were less than the cage controls at the end of suspension, but gradually increased during recovery. However, they were still less than those of the age-matched controls even after 3-month recovery. External bending of shaft and rotation of distal end of tibia were observed in the suspended group and these phenomena were not recovered at all. These morphological changes caused the inhibition of dorsi-flexion of ankle joints. The electromyogram activities of ankle plantar-flexors, soleus, plantaris, lateral gastrocnemius, were inhibited and those of dorsi-flexor, tibialis anterior, were increased during suspension. Typical changes in bone morphology were not induced by exposure to 2-G. It was suggested that gravitational unloading during developing period causes irreversible inhibition of normal bone growth. It was also indicated that the suspension-related changes in bone morphology may be caused by abnormal mechanical stress due to the altered mobilization of hindlimb muscles.     

Irreversible morphological changes in leg bone following chronic gravitational unloading of growing rats

Effects of gravitational unloading or loading on the growth and development of hindlimb bones were studied in rats. Male Wistar rats were hindlimb-unloaded or loaded at 2-G from the postnatal day 4 to month 3. The morphology and mineral content of tibia and fibula, as well as the mobility of ankle joints, were measured at the end of 3-month suspension or loading, and 1, 2, and 3 months after ambulation recovery. Growth-related increases of bone weight and mineral density were inhibited by unloading. But they were gradually recovered toward the control levels, even though they were still less than those in the age-matched controls after 3 months. None of the parameters were influenced by 2-G loading. However, here we report that chronic unloading causes abnormal morphological development in hindlimb bone of growing rats. Irreversible external bend of the shaft and rotation of the distal end of tibia, which limit the dorsiflexion of ankle joints, were induced following chronic gravitational unloading during developing period. It is also suggested that such phenomena are caused by the abnormal mechanical forces imposed by muscle utilization with altered patterns. The activity of ankle dorsiflexor was increased and that of plantarflexor was inhibited during unloading.     

Analysis of the Stress and Displacement Distribution of Inferior Tibiofibular Syndesmosis Injuries Repaired with Screw Fixation: A Finite Element Study

Background

Studies of syndesmosis injuries have concentrated on cadaver models. However, they are unable to obtain exact data regarding the stress and displacement distribution of various tissues, and it is difficult to compare models. We investigated the biomechanical effects of inferior tibiofibular syndesmosis injuries (ITSIs) and screw fixation on the ankle using the finite element (FE) method.

Methodology/Principal Findings

A three-dimensional model of a healthy ankle complex was developed using computed tomography (CT) images. We established models of an ITSI and of screw fixation at the plane 2.5 cm above and parallel to the tibiotalar joint surface of the injured syndesmosis. Simulated loads were applied under three conditions: neutral position with single-foot standing and internal and external rotation of the ankle. ITSI reduced contact forces between the talus and fibula, helped periarticular ankle ligaments withstand more load-resisting movement, and increased the magnitude of displacement at the lower extreme of the tibia and fibula. ITSI fixation with a syndesmotic screw reduced contact forces in all joints, decreased the magnitude of displacement at the lower extreme of the tibia and fibula, and increased crural interosseous membrane stress.

Conclusions/significance

Severe syndesmosis injuries cause stress and displacement distribution of the ankle to change multidirectional ankle instability and should be treated by internal fixation. Though the transverse syndesmotic screw effectively stabilizes syndesmotic diastasis, it also changes stress distribution around the ankle and decreases the joint''s range of motion (ROM). Therefore, fixation should not be performed for a long period of time because it is not physiologically suitable for the ankle joint.     

单侧外固定架对胫腓骨严重开放性骨折的临床疗效

目的:探讨单侧外固定架对不同部位胫腓骨严重开放性骨折的临床治疗效果及关节恢复功能情况。方法:回顾性分析我院自2013年1月至2015年1月共收治胫腓骨严重开放骨折行单侧外固定术治疗患者,根据骨折部位的不同将所有病例分为三组,A组12例,为胫腓骨近端骨折或波及膝关节,固定时需要跨膝关节固定,B组30例,为胫腓骨中段骨折,固定时不跨关节,C组18例,为胫腓骨远端骨折或波及踝关节,固定时需跨踝关节固定。分别对其进行单侧外固定架手术治疗,术后对所有患者骨折愈合情况及膝、踝关节活动度统计,对比观察各组手术疗效。结果:所有手术均获得成功,无不良事件发生,A组下肢功能优良率为83.3%;B组为96.7%;C组为83.3%。下肢功能恢复情况B组与A、C组相比差异具有统计学意义(P0.05),A组与C组相比差异无统计学意义(P0.05)。A组膝、踝关节功能恢复优良率分别为膝66.7%,踝91.7%;B组为膝93.3%,踝96.7%;C组为膝94.4%,踝72.2%。膝关节功能恢复情况A组与B、C组相比差异具有统计学意义(P0.05),B组与C组相比差异无统计学意义(P0.05)。踝关节功能恢复情况C组与A、B组相比差异具有统计学意义(P0.05),A组与B组相比差异无统计学意义(P0.05)。结论:单侧外固定架对不同部位胫腓骨严重开放性骨折的治疗效果良好,关节恢复情况满意,值得临床推广。     

Stance and gait in the hindlimb of a therocephalian mammal-like reptile

The ilium, femur, tibia, fibula, astragalus and calcaneum of the therocephalian therapsid Regisaurus jacobi Mendrez are described. Functional consideration of the bones and particularly the nature of the hip, knee and ankle joints indicate that this animal was capable of at least two distinct gaits, a primitive, sprawling type and an advanced upright type. The ankle joint had a moveable articulation between the astragalus and the calcaneum analogous to that of the crocodiles. The possibility of such a multi-gaited intermediate stage having occurred in the course of the evolution of the mammalian locomotory pattern is suggested.     

Relative strength of the tibia and fibula and locomotor behavior in hominoids

The fibula has rarely been considered in comparative morphological studies, probably due to its relatively minor role in carrying mechanical loads. However, some differences in morphology (and inferred function) of the fibula between humans and apes, and within apes, have been noted and related to differences in positional behavior. Therefore, the study of tibiofibular relations may be useful in characterizing such differences. This study examines cross-sectional geometric (CSG) properties (cortical area and polar section modulus, Z(p)) of the tibia and fibula at mid-diaphysis across a sample (n=87) of humans, chimpanzees, gorillas, orangutans, and gibbons. The fibula is compared against the tibia in the different taxa. The results indicate that the robusticity of the fibula relative to that of the tibia can be explained in terms of differences in positional behavior. In particular, hominoids that are more arboreal (i.e., gibbons, orangutans, and chimpanzees) possess a relatively more robust fibula than do hominoids that are more terrestrial (i.e., gorillas and humans). The difference appears to be a consequence of the more mobile fibula and more adducted position of the hindlimb necessary in an arboreal environment. Apart from providing the first CSG data on the fibula, these results may be helpful in reconstructing the locomotor behavior of fossil hominoids.     

Transient and long-time kinetic responses of the cadaveric leg during internal and external foot rotation

The purpose of this study was to determine the long-time and transient characteristics of the moment generated by external (ER) and internal (IR) rotation of the calcaneus with respect to the tibia. Two human cadaver legs were disarticulated at the knee joint while maintaining the connective tissue between the tibia and fibula. An axial rotation of 21° was applied to the proximal tibia to generate either ER or IR while the fibula was unconstrained and the calcaneus was permitted to translate in the transverse plane. These boundary conditions were intended to allow natural motion of the fibula and for the effective applied axis of rotation to move relative to the ankle and subtalar joints based on natural articular motions among the tibia, fibula, talus, and calcaneus. A load cell at the proximal tibia measured all components of force and moment. A quasi-linear model of the moment along the tibia axis was developed to determine the transient and long-time loads generated by this ER/IR. Initially neutral, everted, inverted, dorsiflexed, and plantarflexed foot orientations were tested. For the neutral position, the transient elastic moment was 16.5 N-m for one specimen and 30.3 N-m for the other in ER with 26.3 and 32.1 N-m in IR. The long-time moments were 5.5 and 13.2 N-m (ER) and 9.0 and 9.5 N-m (IR). These loads were found to be transient over time similar to previous studies on other biological structures where the moment relaxed as time progressed after the initial ramp in rotation.     

Anatomy and histochemistry of hindlimb flight posture in birds. I. The extended hindlimb posture of shorebirds

Birds utilize one of two hindlimb postures during flight: an extended posture (with the hip and knee joints flexed, while the ankle joint is extended caudally) or a flexed posture (with the hip, knee, and ankle joints flexed beneath the body). American Avocets (Recurvirostra americana) and Black‐necked Stilts (Himantopus mexicanus) extend their legs caudally during flight and support them for extended periods. Slow tonic and slow twitch muscle fibers are typically found in muscles functioning in postural support due to the fatigue resistance of these fibers. We hypothesized that a set of small muscles composed of high percentages of slow fibers and thus dedicated to postural support would function in securing the legs in the extended posture during flight. This study examined the anatomy and histochemical profile of eleven hindlimb muscles to gain insight into their functional roles during flight. Contrary to our hypothesis, all muscles possessed both fast twitch and slow twitch or slow tonic fibers. We believe this finding is due to the versatility of dynamic and postural functions the leg muscles must facilitate, including standing, walking, running, swimming, and hindlimb support during flight. Whether birds use an extended or flexed hindlimb flight posture may be related to the aerodynamic effect of leg position or may reflect evolutionary history. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Functional morphology of the hindleg in two kangaroos Macropus giganteus and Aepyprymnus rufescens

In this study the structures in the hindleg of the kangaroo which are potentially available for jumping were examined. Specimens of two species, Macropus giganteus and Aepyprymnus rufescens, were examined and are described and compared. The basic pattern of the jump of the two species is similar. This is reflected anatomically by the fact that in both species the extensors of the hip, knee and ankle as a percentage of the total weight of the hindleg are greater than the flexors of the same joints. An additional similarity is that the biceps femoris and adductor magnus have the greatest share in the weight of the hip extensors. Furthermore the estimated total force of the hip, knee and ankle extensors and total moment of the hip and ankle extensors are always greater than the flexors of the same joints. However, the percentage of the hip and knee extensors, the absolute forces and moments of both the extensors and flexors and the range of movement especially of the hip and knee are always greater in M. giganteus than in A. rufescens. As well as these differences, the long tibia and the position of the knee in view of the hip may be important factors for the longer jump achieved by M. giganteus. In comparison A. rufescens has a anatomical construction which seems to be a compromise between walking and jumping.     

Evolution of hindlimb bone dimensions and muscle masses in house mice selectively bred for high voluntary wheel‐running behavior

We have used selective breeding with house mice to study coadaptation of morphology and physiology with the evolution of high daily levels of voluntary exercise. Here, we compared hindlimb bones and muscle masses from the 11th generation of four replicate High Runner (HR) lines of house mice bred for high levels of voluntary wheel running with four non‐selected control (C) lines. Mass, length, diameter, and depth of the femur, tibia‐fibula, and metatarsal bones, as well as masses of gastrocnemius and quadriceps muscles, were compared by analysis of covariance with body mass or body length as the covariate. Mice from HR lines had relatively wider distal femora and deeper proximal tibiae, suggesting larger knee surface areas, and larger femoral heads. Sex differences in bone dimensions were also evident, with males having thicker and shorter hindlimb bones when compared with females. Several interactions between sex, linetype, and/or body mass were observed, and analyses split by sex revealed several cases of sex‐specific responses to selection. A subset of the HR mice in two of the four HR lines expressed the mini‐muscle phenotype, characterized mainly by an ～50% reduction in hindlimb muscle mass, caused by a Mendelian recessive mutation, and known to have been under positive selection in the HR lines. Mini‐muscle individuals had elongated distal elements, lighter and thinner hindlimb bones, altered 3rd trochanter muscle insertion positions, and thicker tibia‐fibula distal widths. Finally, several differences in levels of directional or fluctuating asymmetry in bone dimensions were observed between HR and C, mini‐ and normal‐muscled mice, and the sexes. This study demonstrates that skeletal dimensions and muscle masses can evolve rapidly in response to directional selection on locomotor behavior.     

The line of action in the tibia during axial compression of the leg

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions. For each test, the location and angle of the line of action were calculated at the tibial midshaft. The line of action was extended to the bone ends in order to determine the locations of the effective centers of pressure on the tibial plafond and tibial plateau. The effective center of pressure on the tibial plafond consistently migrated anteriorly in dorsiflexion, laterally in eversion, posteriorly in plantarflexion, and medially in inversion. An opposite pattern was observed on the tibial plateau. When the knee was flexed, the effective center of pressure was generally isolated to a small area in the posterior portion of the medial tibial condyle. The percentage of the axial load borne by the fibula varied from -8% to 19%, and was related to the inversion/eversion angle of the ankle (p<0.02), as well as the distance between the fibula and the axial load path at the midshaft (p<0.001). The line of action through the tibia appeared to follow the external load path to the extent allowed by the available joint contact surfaces.     

Ankle flexor muscles in the cat: Length-active tension and muscle unit properties as related to locomotion

The mechanical properties of the whole muscle and fast-twitch muscle units of the cat hindlimb pretibial flexors have been explored and related to normal locomotion. Tibialis anterior (TA) is parallel-fibered and functionally crosses a single joint, the ankle, whereas extensor digitorum longus (EDL) is pinnate and spans the ankle, knee, metatarsophalangeal and interphalangeal joints. The active tetanic tension of TA remains near its peak value over a range of muscle lengths associated with normal ankle movement. In contrast, the length-tension curve of EDL is sharply peaked. However, normal corollary action of the knee, ankle and metatarsophalangeal joints during stepping minimizes EDL's excursion and maintains it at or near a length optimal for peak tension development. EDL is capable of producing synchronous but sterotyped digit and ankle movements while TA provides for independent ankle flexion at all relevant joint angles. The mechanical properties of 84 TA and 98 EDL fast-twitch muscle units were studied by measuring twitch contraction time (≤45 msec), peak tetanic tension, response to repetitive stimulation, and contractile fatigue resistance during electrical stimulation of single alpha axons, functionally isolated from ventral root filaments. These mechanical properties were essentially similar for both muscles with the exception of mean peak tetanic tension which was 30% lower for TA units (14 gm-wt) than for EDL units (20 gm-wt). A high proportion of units in both muscles demonstrated fatigue resistance which is reflective of the repetitive, phasic demand upon these muscles during locomotion.     

Design of a controlled-release ergometer for the measurement of musculotendinous stiffness of the knee flexors

The stiffness of muscle-tendon units (MTUs) influences many aspects of human movement from athletic performance to injury risk. Presently the controlled-release technique of measuring MTU stiffness has been applied almost exclusively to the distal joints of the body, i.e., the ankle. This is primarily because of the mechanical limitations of implementing this technique. However, in order to better understand how the elastic properties of the MTU affect both performance and injury potential, measurements of MTU stiffness of the more proximal joints must be made. The knee flexors are a logical choice because of the integral role of MTU stiffness of this muscle group in both hamstring strains and knee injury. The purpose of this study was to modify a commercial ergometer so that it could be used to measure the musculotendinous stiffness of the knee flexors. Data are presented for a representative participant to illustrate the feasibility and capability of this ergometer, and the measured MTU stiffness was 519 N.m.rad(-1) at a knee flexion moment of 100 N.m. Our results indicate that it is indeed possible to modify a commercial ergometer and measure musculotendinous stiffness of large muscle groups crossing proximal joints.     

Analysis of surface-to-surface distance mapping during three-dimensional motion at the ankle and subtalar joints

Joint surface interaction and ligament constraints determine the kinematic characteristics of the ankle and subtalar joints. Joint surface interaction is characterized by joint contact mechanics and by relative joint surface position potentially characterized by distance mapping. While ankle contact mechanics was investigated, limited information is available on joint distance mapping and its changes during motion. The purpose of this study was to use image-based distance mapping to quantify this interaction at the ankle and subtalar joints during tri-planar rotations of the ankle complex. Five cadaveric legs were scanned using Computed Tomography and the images were processed to produce 3D bone models of the tibia, fibula, talus and calcaneus. Each leg was tested on a special linkage through which the ankle complex was loaded in dorsiflexion/plantarflexion, inversion/eversion, and internal/external rotation and the resulting bone movements were recorded. Fiduciary bone markers data and 3D bone models were combined to generate color-coded distance maps for the ankle and subtalar joints. The results were processed focusing on the changes in surface-to-surface distance maps between the extremes of the range of motion and neutral. The results provided detailed insight into the three-dimensional highly coupled nature of these joints showing significant and unique changes in distance mapping from neutral to extremes of the range of motion. The non-invasive nature of the image-based distance mapping technique could result, after proper modifications, in an effective diagnostic and clinical evaluation technique for application such as ligament injuries and quantifying the effect of arthrodesis or total ankle replacement surgery.     

Hox11 genes establish synovial joint organization and phylogenetic characteristics in developing mouse zeugopod skeletal elements

Hox11 genes are essential for zeugopod skeletal element development but their roles in synovial joint formation remain largely unknown. Here, we show that the elbow and knee joints of mouse embryos lacking all Hox11 paralogous genes are specifically remodeled and reorganized. The proximal ends of developing mutant ulna and radius elements became morphologically similar and formed an anatomically distinct elbow joint. The mutant ulna lacked the olecranon that normally attaches to the triceps brachii muscle tendon and connects the humerus to the ulna. In its place, an ulnar patella-like element developed that expressed lubricin on its ventral side facing the joint and was connected to the triceps muscle tendon. In mutant knees, both tibia and fibula fully articulated with an enlarged femoral epiphyseal end that accommodated both elements, and the neo-tripartite knee joint was enclosed in a single synovial cavity and displayed an additional anterior ligament. The mutant joints also exhibited a different organization of the superficial zone of articular cartilage that normally exerts an anti-friction function. In conclusion, Hox11 genes co-regulate and coordinate the development of zeugopod skeletal elements and adjacent elbow and knee joints, and dictate joint identity, morphogenesis and anatomical and functional organization. Notably, the ulnar patella and tripartite knee joints in the mouse mutants actually characterize several lower vertebrates, including certain reptiles and amphibians. The re-emergence of such anatomical structures suggests that their genetic blueprint is still present in the mouse genome but is normally modified to the needs of the mammalian joint-formation program by distinct Hox11 function.     

Multi-functionality of the cat medical gastrocnemius during locomotion

The functional role of biarticular muscles was investigated based on direct force measurement in the cat medial gastrocnemius (MG) and analysis of hindlimb kinematics and kinetics for the stance phase of level, uphill, and downhill walking. Four primary functional roles of biarticular muscles have been proposed in the past. These functional roles have typically been discussed independently of each other, and biarticular muscles have rarely been assigned more than one functional roles for different phases of the work cycle. The purpose of this study was to elucidate the functional role of the biarticular cat MG during locomotion. It was found that MG forces were primarily associated with the moment requirements at the ankle for most of the stance phase, but also helped to satisfy the moments at the knee in the initial phase of stance. In the second half of stance, MG transferred mechanical energy from the knee to the ankle from the knee to the ankle, while simultaneously producing a substantial amount of mechanical work. Based on these results, we hypothesize that MG's primary function is that of an ankle extensor. However, because of the coupling of the ankle extensor moment with a knee flexor moment in the initial, and a knee extensor moment in the final phase of stance, MG satisfies two joint moments in early stance, and transfers mechanical energy from the knee to the ankle in late stance. We conclude that cat MG has multiple functional roles during the stance phase of locomotion, and speculate that such multi-functionality also exists in other bi- and multi-articular muscles.     

The role of intersegmental dynamics during rapid limb oscillations

The interactive dynamic effects of muscular, inertial and gravitational moments on rapid, multi-segmented limb oscillations were studied. Using three-segment, rigid-body equations of motion, hip, knee and ankle intersegmental dynamics were calculated for the steady-state cycles of the paw-shake response in adult spinal cats. Hindlimb trajectories were filmed to obtain segmental kinematics, and myopotentials of flexors and extensors at each of the three joints were recorded synchronously with the ciné film. The segmental oscillations that emerged during the paw-shake response were a consequence of an interplay between active and passive musculotendinous forces, inertial forces, and gravity. During steady-state oscillations, the amplitudes of joint excursions, peak angular velocities, and peak angular accelerations increased monotonically and significantly in magnitude from the proximal joint (hip) to the most distal joint (ankle). In contrast to these kinematic relationships, the maximal values of net moments at the hip and knee were equal in magnitude, but of significantly lower magnitude than the large net moment at the ankle joint. At both the ankle and the knee, the flexor and extensor muscle moments were equal, but at the hip the magnitude of the peak flexor muscle moment was significantly greater than the extensor muscle moment. Muscle moments at the hip not only acted to counterbalance accelerations of the more distal segments, but also acted to maintain the postural orientation of the hindlimb. Large muscle moments at the knee functioned to counterbalance the large inertial moments generated by the large angular accelerations of the paw. At the ankle, the muscle moments dominated the generation of the paw accelerations. At the ankle and the knee, muscle moments controlled limb dynamics by slowing and reversing joint motions, and the active muscle forces contributing to ankle and knee moments were derived from lengthening of active musculotendinous units. In contrast to the more distal joints, the active muscles crossing the hip predominantly shortened as a result of the interplay among inertial forces and gravitational moments. The muscle function and kinetic data explain key features of the complex interactions that occur between central control mechanisms and multi-segmented, oscillating limb segments during the paw-shake response.     

Inter-segmental coordination: motor pattern in humans stepping over an obstacle with mechanical ankle joint friction

This study examined the influence of a mechanical perturbation of the ankle joint on obstacle avoidance pattern. A decoupled control between the distal joint and the combined (hip-knee) proximal joints was observed according to the task requirement. In this context, a greater mechanical friction at the ankle should be compensated at this joint (local compensation) or alternatively, by regulating more combined proximal joints (knee and/or hip). The leading limb inter-segmental coordination was evaluated in both no constraint and constraint conditions in calculating ranges of motion (ROM), moments of force and powers (from heel-off to obstacle) at the ankle, knee and hip joints. Electromyographic activities were also analyzed. With the constraint, the dorsiflexor moment and the tibialis anterior activity remained unchanged while both ROM and power bursts (absorbed and generated) decreased. The hip and knee ROM remain invariant. At heel-off the absorption by hip extensors decreased and the forthcoming generation by knee flexors increased in the constraint condition. To quantify the inter-joint coordination, principal component analysis was used and indicated a high level of inter-joint coupling (synergy) that decreased with the constraint (i.e. less inter-joint coupling). At the ankle joint, the results suggest that the central command was the same in both conditions thus, not be adapted. At both the hip and knee joints, a combined joints modulation occurred to overcome additional friction.