Joint Coupling Research Articles

Multidimensional joint coupling: a case study visualisation approach to movement coordination and variability

A case study visualisation approach to examining the coordination and variability of multiple interacting segments is presented using a whole-body gymnastic skill as the task example. One elite male gymnast performed 10 trials of 10 longswings whilst three-dimensional locations of joint centres were tracked using a motion analysis system. Segment angles were used to define coupling between the arms and trunk, trunk and thighs and thighs and shanks. Rectified continuous relative phase profiles for each interacting couple for 80 longswings were produced. Graphical representations of coordination couplings are presented that include the traditional single coupling, followed by the relational dynamics of two couplings and finally three couplings simultaneously plotted. This method highlights the power of visualisation of movement dynamics and identifies properties of the global interacting segmental couplings that a more formal analysis may not reveal. Visualisation precedes and informs the appropriate qualitative and quantitative analysis of the dynamics.

Effect of distal interphalangeal joint fusion of the index or middle finger on the grip or finger force and load distribution in the hand

Due to the functional coupling of adjacent finger joints and the quadriga effect of the flexor digitorum profundus an influence of the grip pattern of the hand after fusion of a distal interphalangeal joint (DIPJ) is assumed. Two patients with DIPJ II- fusion and 8 patients with DIPJ III- fusion due to a posttraumatic osteoarthritis, but without any other pathology of both hands were assessed on average 55 (17-121) months postoperatively by manugraphy. Using three sizes of cylinders the total grip force and the load distribution of the hand and each finger were measured. The grip pattern was analyzed by 2D-graphs. The results of the affected hand were compared to the healthy opposite side. The consolidation of the DIPJ arthrodesis was confirmed and the angle of the joint fusion measured by radiographs. Patients rated their pain in rest or under strain by a visual analogue scale. The total grip force of the affected hand compared to the opposite side was 93 % for the small cylinder, 97 % for the middle, and 96 % for the large cylinder. Both patients with a DIPJ II- fusion neglected the index finger considerably and had a remarkably weak grip force (68/62/68 % for the 3 cylinders respectively). The grip pattern of all fingers has changed. Eight patients with DIPJ III- fusion averaged 99/106/103 % grip force. In six of them, the affected hand was stronger than the opposite hand when using the middle cylinder. The finger force of the middle and ring finger was reduced, but of the index and little finger increased. Five patients had a striking peak of local pressure at the fused DIPJ III.The angle of the fused DIPJ averaged 6° (0-21°) for all patients. Pain was rated on average 1.4 (0-5) at rest and 2 (0-8) with strain. Both aspects were not found to influence the grip force or the load distribution. After DIPJ- fusion of the middle finger its finger force is reduced; but, the total grip force is compensated by an increased finger force of the index and little finger. Despite limitations due to the small number of patients, a DIPJ II- fusion might have a considerable effect on grip force and load distribution of the hand rather due to omitting this finger than purely biomechanical effects.

Neural network model reference decoupling control for single leg joint of hydraulic quadruped robot

PurposeTo control one of the joints during the actual movement of the hydraulically driven quadruped robot, all the other joints in the leg need to be locked. Once the joints are unlocked, there is a coupling effect among the joints. Therefore, during the normal exercise of the robot, the movement of each joint is affected by the coupling of other joints. This brings great difficulties to the coordinated motion control of the multi-joints of the robot. Therefore, it is necessary to reduce the influence of the coupling of the hydraulically driven quadruped robot.Design/methodology/approachTo solve the coupling problem with the joints of the hydraulic quadruped robot, based on the principle of mechanism dynamics and hydraulic control, the dynamic mathematical model of the single leg mechanism of the hydraulic quadruped robot is established. On this basis, the coupling dynamics model of the two joints of the thigh and the calf is derived. On the basis of the multivariable decoupling theory, a neural network (NN) model reference decoupling controller is designed.FindingsThe simulation and prototype experiment are carried out between the thigh joint and the calf joint of the hydraulic quadruped robot, and the results show that the proposed NN model reference decoupling control method is effective, and this method can reduce the cross-coupling between the thigh and the calf and improve the dynamic characteristics of the single joint of the leg.Practical implicationsThe proposed method provides technical support for the mechanical–hydraulic cross-coupling among the joints of the hydraulic quadruped robot, achieving coordinated movement of multiple joints of the robot and promoting the performance and automation level of the hydraulic quadruped robot.Originality/valueOn the basis of the theory of multivariable decoupling, a new decoupling control method is proposed, in which the mechanical–hydraulic coupling is taken as the coupling behavior of the hydraulic foot robot. The method reduces the influence of coupling of system, improves the control precision, realizes the coordinated movement among multiple joints and promotes the popularization and use of the hydraulically driven quadruped robot.

A novel approach for the detection and exploration of joint coupling patterns in the lower limb kinetic chain

BackgroundA comprehensive perspective on foot and lower limb joint coupling is lacking since previous studies did not consider the multi-articular nature of the foot and lower limb neither accounted for biomechanical heterogeneity. Research questionThe current manuscript describes a novel methodological process for detection and exploration of joint coupling patterns in the lower limb kinetic chain. MethodsThe first stage of the methodological process encompasses the measurement of 3D joint kinematics of the foot and lower limb kinetic chain during dynamic activities. The second stage consists of selecting the kinematic waveforms of interest. In the third stage, cross-correlation coefficients are calculated across the selected one-dimensional continua of each subject. In the fourth stage, all cross-correlation coefficients per subject are used as input variable in a cluster algorithm. Algorithm specific qualitative metrics are subsequently considered to determine the most robust clustering. Finally, in the fifth stage the process of biomechanical interpretation is initiated and further exploration is recommended by triangulating with other biomechanical variables. ResultsA first clinical illustration of the novel method was provided using data of fourteen young elite athletes. Cross-correlation coefficients for each leg were calculated across continua of the pelvis, hip, knee, rear foot and midfoot. A hierarchical clustering approach stratified the coefficients into two distinct clusters which was mainly guided by the frontal plane knee kinematics. Both clustered differed significantly from each other with respect to their frontal plane ankle, knee and hip kinetics. SignificanceThe presented method seems to provide a valuable approach to gain insight into foot and lower joint coupling.

Calcaneal adduction and eversion are coupled to talus and tibial rotation.

The purpose of this study was to quantify isolated coupling mechanisms of calcaneal adduction/abduction and calcaneal eversion/inversion to proximal bones invitro. The invitro approach is necessary because invivo both movements appear together, making it impossible to determine the extent of their individual contribution to overall ankle joint coupling. Eight fresh frozen foot-leg specimens were tested. Data describing bone orientation and coupling mechanisms between segments were obtained using bone pin marker triads. The bone movement was described in a global coordinate system to examine the coupling between the calcaneus, talus and tibia. The strength of coupling was determined by means of the slope of a linear least squares fit to an angle-angle plot. The coupling coefficients in the present study indicate that not only calcaneal eversion/inversion (coupling coefficient: 0.68±0.15) but to an even greater extent calcaneal adduction/abduction (coupling coefficient: 0.99±0.10) was transferred into talus and tibial rotation, highlighting the relevance of calcaneal adduction for the overall ankle joint coupling. The results of this study present the possibility that controlling calcaneal adduction/abduction can affect talus and tibial rotation and therefore the possible genesis of overuse knee injuries.

Toward Controllable Hydraulic Coupling of Joints in a Wearable Robot.

In this paper, we develop theoretical foundations for a new class of rehabilitation robot: body powered devices that route power between a user's joints. By harvesting power from a healthy joint to assist an impaired joint, novel bimanual and self-assist therapies are enabled. This approach complements existing robotic therapies aimed at promoting recovery of motor function after neurological injury. We employ hydraulic transmissions for routing power, or equivalently for coupling the motions of a user's joints. Fluid power routed through flexible tubing imposes constraints within a limb or between homologous joints across the body. Variable transmissions allow constraints to be steered on the fly, and simple valve switching realizes free space and locked motion. We examine two methods for realizing variable hydraulic transmissions: using valves to switch among redundant cylinders (digital hydraulics) or using an intervening electromechanical link. For both methods, we present a rigorous mathematical framework for describing and controlling the resulting constraints. Theoretical developments are supported by experiments using a prototype fluid-power exoskeleton.

Increased movement variability in one-leg hops about 20 years after treatment of anterior cruciate ligament injury

BackgroundRecent studies highlight the need for understanding movement control of adjacent joints when evaluating knee function following anterior cruciate ligament (ACL) injury. However, while short-term adaptations to lower-extremity joint coupling have been studied, little is known about any potential long-term adaptations in neuromuscular control displayed by ACL-injured individuals. The aim of our study was to determine whether coordination variability of the hip-knee joint couplings during the one-leg hop is altered about 20 years after injury in two ACL-injured groups compared to healthy knee controls. MethodsSeventy persons performed one leg hops ~23 years after ACL injury and following different treatments: 33 participants treated with physiotherapy in combination with ACL-reconstruction (ACLR); 37 participants with physiotherapy alone (ACLPT). They were compared to 33 matched controls. A vector coding procedure was used to create joint couplings for knee and hip angles on all the cardinal planes for the Take-off and Landing phases. The standard deviation of each coupling was computed as a measure of coordination variability. FindingsBoth the ACL groups differed significantly from controls on their injured side with ~50% higher knee abduction-adduction/hip internal-external rotation variability during the Take-off phase; ~33% higher knee abduction-adduction/knee flexion-extension variability and greater knee abduction-adduction/hip flexion-extension variability (ACLR 50%; ACLPT 80%) during the Landing phase. There were no major differences between injured and non-injured sides in any group. InterpretationIncreased variability in lower-extremity joint couplings has emerged as a conspicuous feature of ACL injured persons in the very long term compared to non-injured controls, independent of treatment. Further research of the processes leading to alterations in movement variability using longitudinal studies would facilitate better understanding of the functional adaptations leading to knee dysfunction in the short- and long-term after ACL injury.

Static analysis of thin-walled space frame structures with arbitrary closed cross-sections using transfer matrix method

This paper develops a new transfer matrix method for the static analysis of thin-walled space frame structures with arbitrary closed single-cell sections, that is, thin-walled beam transfer matrix method (TBTMM), which expands the advantages of the general transfer matrix method (TMM). In this method, the bimoment B and the rate of twist of the beam φ(x) are taken into account based on the Vlasov's beam theory and Kollbrunner-Hajdin assumption, and the bending and twisting can be calculated separately combined with the characteristic of Maillart's shear center. Using this method, the transfer matrix of single beam is obtained through Laplace transform and inverse Laplace transform at first, and then gets the coupling equations of the whole structure with respect to coordinate transformation matrices and joint coupling matrices. Some numerical examples are given and compared with the general TMM and the finite element method (B-FEM and S-FEM) results to validate the developed method.

Patterns of intermuscular inhibitory force feedback across cat hindlimbs suggest a flexible system for regulating whole limb mechanics.

Prior work has suggested that Golgi tendon organ feedback, via its distributed network linking muscles spanning all joints, could be used by the nervous system to help regulate whole limb mechanics if appropriately organized. We tested this hypothesis by characterizing the patterns of intermuscular force-dependent feedback between the primary extensor muscles spanning the knee, ankle, and toes in decerebrate cat hindlimbs. Intermuscular force feedback was evaluated by stretching tendons of selected muscles in isolation and in pairwise combinations and then measuring the resulting force-dependent intermuscular interactions. The relative inhibitory feedback between extensor muscles was examined, as well as symmetry of the interactions across limbs. Differences in the directional biases of inhibitory feedback were observed across cats, with three patterns identified as points on a spectrum: pattern 1, directional bias of inhibitory feedback onto the ankle extensors and toe flexors; pattern 2, convergence of inhibitory feedback onto ankle extensors and mostly balanced inhibitory feedback between vastus muscle group and flexor hallucis longus, and pattern 3, directional bias of inhibitory feedback onto ankle and knee extensors. The patterns of inhibitory feedback, while different across cats, were symmetric across limbs of individual cats. The variable but structured distribution of force feedback across cat hindlimbs provides preliminary evidence that inhibitory force feedback could be a regulated neural control variable. We propose the directional biases of inhibitory feedback observed experimentally could provide important task-dependent benefits, such as directionally appropriate joint compliance, joint coupling, and compensation for nonuniform inertia. NEW & NOTEWORTHY Feedback from Golgi tendon organs project widely among extensor motor nuclei in the spinal cord. The distributed nature of force feedback suggests these pathways contribute to the global regulation of limb mechanics. Analysis of this network in individual animals indicates that the strengths of these pathways can be reorganized appropriately for a variety of motor tasks, including level walking, slope walking, and landing.

Simulating the impact of sensorimotor deficits on reaching performance.

The healthy human nervous system accurately and robustly controls movements despite nonlinear dynamics, noise, and delays. After a stroke, motor ability frequently becomes impaired. To provide insight into the relative impact of specific sensorimotor deficits on motor performance, we modeled neural control of reaching with the human upper limb as a near-optimally feedback-controlled two-degree-of-freedom system with biologically based parameters. We added three sensorimotor impairments commonly associated with post-stroke hemiparesis - abnormal joint coupling, increased noise on internally modeled dynamics, and muscular weakness - and examined the impact on reaching performance. We found that abnormal joint coupling unknown to the system's internal model caused systematic perturbations to trajectories, longer reach durations, and target overshoot. Increasing internal model noise and muscular weakness had little impact on motor performance unless model noise was increased by several orders of magnitude. Many reaches performed by our perturbed models replicate features commonly observed in reaches by hemiparetic stroke survivors. The sensitivity to unmodeled abnormal joint coupling agrees with experimental findings that abnormal coupling (possibly related to internal model errors) is the main cause of post-stroke motor impairment.

Lower extremity joint coupling variability during gait in young adults with and without chronic ankle instability

Chronic ankle instability (CAI) is a condition resulting from a lateral ankle sprain. Shank-rearfoot joint-coupling variability differences have been found in CAI patients; however, joint-coupling variability (VCV) of the ankle and proximal joints has not been explored. Our purpose was to analyse VCV in adults with and without CAI during gait. Four joint-coupling pairs were analysed: knee sagittal-ankle sagittal, knee sagittal-ankle frontal, hip frontal-ankle sagittal and hip frontal-ankle frontal. Twenty-seven adults participated (CAI:n = 13, Control:n = 14). Lower extremity kinematics were collected during walking (4.83 km/h) and jogging (9.66 km/h). Vector-coding was used to assess the stride-to-stride variability of four coupling pairs. During walking, CAI patients exhibited higher VCV than healthy controls for knee sagittal-ankle frontal in latter parts of stance thru mid-swing. When jogging, CAI patients demonstrated lower VCV with specific differences occurring across various intervals of gait. The increased knee sagittal-ankle frontal VCV in CAI patients during walking may indicate an adaptation to deal with the previously identified decrease in variability in transverse plane shank and frontal plane rearfoot coupling during walking; while the decreased ankle-knee and ankle-hip VCV identified in CAI patients during jogging may represent a more rigid, less adaptable sensorimotor system ambulating at a faster speed.

Upper Extremity Motor Impairments and Microstructural Changes in Bulbospinal Pathways in Chronic Hemiparetic Stroke

Following hemiparetic stroke, precise, individuated control of single joints is often replaced by highly stereotyped patterns of multi-joint movement, or abnormal limb synergies, which can negatively impact functional use of the paretic arm. One hypothesis for the expression of these synergies is an increased dependence on bulbospinal pathways such as the rubrospinal (RubST) tract and especially the reticulospinal (RetST) tracts, which co-activate multiple muscles of the shoulder, elbow, wrist, and fingers. Despite indirect evidence supporting this hypothesis in humans poststroke, it still remains unclear whether it is correct. Therefore, we used high-resolution diffusion tensor imaging (DTI) to quantify white matter microstructure in relation to severity of arm synergy and hand-related motor impairments. DTI was performed on 19 moderately to severely impaired chronic stroke individuals and 15 healthy, age-matched controls. In stroke individuals, compared to controls, there was significantly decreased fractional anisotropy (FA) and significantly increased axial and radial diffusivity in bilateral corona radiata and body of the corpus callosum. Furthermore, poststroke, the contralesional (CL) RetST FA correlated significantly with both upper extremity (UE) synergy severity (r = −0.606, p = 0.003) and hand impairment (r = −0.609, p = 0.003). FA in the ipsilesional RubST significantly correlated with hand impairment severity (r = −0.590, p = 0.004). For the first time, we separately evaluate RetST and RubST microstructure in chronic stroke individuals with UE motor impairment. We demonstrate that individuals with the greatest UE synergy severity and hand impairments poststroke have the highest FA in the CL RetST a pattern consistent with increased myelination and suggestive of neuroplastic reorganization. Since the RetST pathway microstructure, in particular, is sensitive to abnormal joint coupling and hand-related motor impairment in chronic stroke, it could help test the effects of specific, and novel, anti-synergy neurorehabilitation interventions for recovery from hemiparesis.

Foot segmental motion and coupling in stage II and III tibialis posterior tendon dysfunction

BackgroundClassification systems developed in the field of posterior tibialis tendon dysfunction omit to include dynamic measurements. Since this may negatively affect the selection of the most appropriate treatment modality, studies on foot kinematics are highly recommended. Previous research characterised the foot kinematics in patients with posterior tibialis tendon dysfunction. However, none of the studies analysed foot segmental motion synchrony during stance phase, nor compared the kinematic behaviour of the foot in presence of different posterior tibialis tendon dysfunction stages. Therefore, we aimed at comparing foot segmental motion and coupling in patients with posterior tibialis tendon dysfunction grade 2 and 3 to those of asymptomatic subjects. MethodsFoot segmental motion of 11 patients suffering from posterior tibialis tendon dysfunction stage 2, 4 patients with posterior tibialis tendon dysfunction stage 3 and 15 asymptomatic subjects was objectively quantified with the Rizzoli foot model using an instrumented walkway and a 3D passive motion capture system. Dependent variables were the range of motion occurring at the different inter-segment angles during subphases of stance and swing phase as well as the cross-correlation coefficient between a number of segments. ResultsSignificant differences in range of motion were predominantly found during the forefoot push off phase and swing phase. In general, both patient cohorts demonstrated a reduced range of motion compared to the control group. This hypomobility occurred predominantly in the rearfoot and midfoot (p<0.01). Significant differences between both posterior tibialis tendon dysfunction patient cohorts were not revealed. Cross-correlation coefficients highlighted a loss of joint coupling between rearfoot and tibia as well as between rearfoot and forefoot in both posterior tibialis tendon dysfunction groups. InterpretationThe current evidence reveals considerable mechanical alterations in the foot which should be considered in the decision making process since it may help explaining the success and failure of certain conservative and surgical interventions.

A Unified Theory of Neuro-MRI Data Shows Scale-Free Nature of Connectivity Modes.

A primary goal of many neuroimaging studies that use magnetic resonance imaging (MRI) is to deduce the structure-function relationships in the human brain using data from the three major neuro-MRI modalities: high-resolution anatomical, diffusion tensor imaging, and functional MRI. To date, the general procedure for analyzing these data is to combine the results derived independently from each of these modalities. In this article, we develop a new theoretical and computational approach for combining these different MRI modalities into a powerful and versatile framework that combines our recently developed methods for morphological shape analysis and segmentation, simultaneous local diffusion estimation and global tractography, and nonlinear and nongaussian spatial-temporal activation pattern classification and ranking, as well as our fast and accurate approach for nonlinear registration between modalities. This joint analysis method is capable of extracting new levels of information that is not achievable from any of those single modalities alone. A theoretical probabilistic framework based on a reformulation of prior information and available interdependencies between modalities through a joint coupling matrix and an efficient computational implementation allows construction of quantitative functional, structural, and effective brain connectivity modes and parcellation. This new method provides an overall increase of resolution, accuracy, level of detail, and information content and has the potential to be instrumental in the clinical adaptation of neuro-MRI modalities, which, when jointly analyzed, provide a more comprehensive view of a subject's structure-function relations, while the current standard, wherein single-modality methods are analyzed separately, leaves a critical gap in an integrated view of a subject's neuorphysiological state. As one example of this increased sensitivity, we demonstrate that the jointly estimated structural and functional dependencies of mode power follow the same power law decay with the same exponent.

Assessment of patterns and variability in lower extremity coordination between genders with different shoe insole stiffness during jump-landing tasks

PurposeThe study aims to examine how shoe insole cushioning can influence coordination pattern and variability in males and females during the landing phase of a jump-landing task. Methods. Twenty participants (10 males and 10 females) performed jump-landing tasks, and the continuous relative phase (CRP) and the variability of CRP in foot-shank and shank-thigh couplings were determined during the landing phase.ResultsWomen represented lower CRP and CRP variability of foot-shank coupling in non-insole conditions (&lt;i&gt;p&lt;/i&gt; &lt; 0.05). Shoe insole stiffness had no significant effect on CRP or variability in CRP (&lt;i&gt;p&lt;/i&gt; &gt; 0.05).ConclusionsAlthough females are characterised by lower coupling variability in non-insole conditions, they do have the capacity to achieve similar coordination patterns and variability as males, in soft and hard conditions. These findings suggest that with changes in the shoe insole, females can achieve similar joint coupling coordination patterns and variability as compared with males under soft and stiff conditions. In addition, as per this study, changes in shoe insole stiffness may not have an impact on coordinative strategies or variability of lower extremity joints couplings during landing.

Tibial rotation in running: Does rearfoot adduction matter?

ObjectiveTo quantify the magnitude of global rearfoot motion, in particular, rearfoot adduction and to investigate its relationship to tibial rotation. DesignOne hundred and four participants ran barefoot on an Ethylene Vinyl Acetate (EVA) foam. Global range of motion values for the shank, rearfoot and medial metatarsal segment as well as foot motion within the transverse plane were determined using an optoelectric motion capture system. Relationships between parameters were assessed using partial correlation analysis. ResultsGlobal rearfoot adduction amounts to 6.1° (±2.7). Furthermore global rearfoot adduction and rearfoot eversion were significantly related to internal tibial rotation (partial correlation: r=0.37, p<0.001 and r=−0.24, p=0.015, respectively). Furthermore, a strong relationship between rearfoot adduction and transverse within foot motion (r=−0.65, p<0.001) was found. ConclusionNext to rearfoot eversion, rearfoot adduction may be also important to the understanding of ankle joint coupling. Controlling rearfoot adduction and transverse within foot motion may be a mechanism to control excessive tibial rotation.

The effects of fatigue on lower extremity kinematics, kinetics and joint coupling in symptomatic female runners with iliotibial band syndrome

BackgroundAltered hip and knee kinematics and joint coupling have been documented in runners with iliotibial band syndrome. Symptoms often present themselves after several minutes of running, yet the effect of fatigue warrants further exploration. The purpose of this study was to determine the effect of a run to fatigue in runners with iliotibial band syndrome, as compared to healthy controls. MethodsTwenty uninjured and 12 female runners with iliotibial band syndrome performed a treadmill run to fatigue. Prior-to and following a run to fatigue, overground running data were collected. Variables of interest included stance phase: peak hip adduction and internal rotation, peak hip abductor and external rotator joint moments and frontal-sagittal plane hip and knee joint coupling. FindingsFatigue resulted in decreased peak hip adduction angles in injured runners. Fatigue did not affect injured runners differently than controls with respect to the remaining variables. Coupling differences did not exist between healthy and injured runners with respect to the loading or propulsive phases of stance. InterpretationWhile clinicians often strengthen hip abductor muscles and provide gait re-training to decrease stance phase hip adduction, our results suggest that, when exerted, female runners with iliotibial band syndrome independently modify their running gait to decrease hip adduction, potentially as a result of pain. Fatigue did not have an effect on the remaining study variables. It is possible that reducing the length of the iliotibial band through minimizing hip adduction reduces pain, but the other variables examined are not sensitive to this phenomenon.

The Effects of Trunk Fatigue on Proximal Joint Kinematics and Coupling During Running

Fatigue is a risk factor for injury and may alter neuromuscular coordination. The trunk accounts for a large percentage of overall body mass and relies on local musculature to control the body’s center of mass (COM). As the trunk fatigues, it has a reduced ability to control the COM and may alter joint mechanics and coordination leading to injury. PURPOSE: To determine how trunk fatigue changes trunk and pelvis excursion and coupling during running. METHODS: Instrumented gait analysis was performed on 32 subjects (16 M, age 21 ± 3 yrs, H: 1.7 ± 0.1 m, M: 65.3 ± 12.5 kg, Tegner: 6.4 ± 1.3). Subjects ran at a self-selected speed (3.1 ± 0.5 m/s) until reporting a 14 on the Borg scale. Next, the subjects performed a trunk fatiguing circuit. Once fatigued, the subjects ran at their previous speed for a 2nd gait analysis. Visual3D and MATLAB were used to calculate joint excursion and angle-angle plots for the trunk and pelvis motions during the stance phase of running. A line of best fit was applied to all angle-angle plots to assess joint coupling. Paired t-tests were used to test differences between the fresh and fatigued conditions. RESULTS: There was a significant reduction in pelvic excursion when fatigued in all three planes (Table 1). There were no significant differences in trunk or hip excursion or joint coupling between the fresh and fatigued states. CONCLUSIONS: Reduced pelvic excursion may be an adaptation to reduce the work the trunk muscles perform. However, no changes in joint coupling were found suggesting that coordination patterns within limbs are maintained. Potentially, trunk fatigue may affect conditions such as anterior knee pain which have been linked to altered pelvic mechanics. Research reported was supported through grant number TL1TR00015.

Foot Joint Coupling Variability in Rearfoot and Forefoot Runners After an Exhaustive Run

While most runners use a rearfoot strike (RFS), recent research suggests that midfoot or forefoot strike (FFS) running is more natural and reduces injuries. Joint coupling is believed to be an important factor in running related injuries. Further, according to the dynamical systems theory, increased joint coupling variability while running may prevent repetitive loading of tissues which may lead to overuse injury. PURPOSE: This study compared joint coupling variability of the foot in habitual RFS and FFS runners prior to and following an exhaustive run. METHODS: Fifteen FFS and 15 RFS runners performed a maximal 5 km treadmill run. Foot motion was assessed using a 7-segment foot model which identified 6 functional articulations (rearfoot, medial midfoot, lateral midfoot, medial forefoot, lateral forefoot, and 1st metatarsophalangeal). Motion capture data was collected for 10 s at the beginning and end of the run and 5 steps were processed for subsequent analysis. Vector coding methods were used to calculate 10 different joint couples. Standard deviations of the coupling angles were used to identify variability within the first 2 subphases of stance (0-20% and 21-50% stance). Mixed between-within subjects ANOVAs were used to compare differences between the foot strikes and pre and post run. RESULTS:Subphase 1: FFS group had increased variability over RFS group in 2 medial midfoot-forefoot couples (1.22° and 2.84° difference) while RFS group had increased coupling variability in 1 lateral midfoot-forefoot couple (0.94° difference). Subphase 2: RFS group had increased variability in 3 rearfoot-midfoot couplings over FFS group (3.43°, 3.66°, and 1.30° difference). Subphase 2 post run, both groups increased variability in rearfoot (0.68° difference pre to post run) and 3 rearfoot-midfoot couplings (0.77°, 0.65°, and 0.84° difference). An interaction occurred between group and pre-post run in the midfoot-forefoot where only RFS runners decreased variability over time (0.99°). CONCLUSION: FFS runners had greater variability in subphase 1, while RFS had greater variability in subphase 2 indicating that a FFS may provide better injury protection during the initial heel strike period. Increased variability post-run in subphase 2 suggests that overstressing tissues may be more critical to prevent during subphase 2.

Effects of aging and Parkinson's disease on joint coupling, symmetry, complexity and variability of lower limb movements during gait

BackgroundNatural aging and disease processes such as Parkinson's disease often lead to gait impairment. This impairment often manifests as changes in symmetry, complexity, and variability of lower limb joint movements during gait as compared to young healthy adults. Current gait assessment tools primarily focus on discrete events during gait or are based on univariate statistical techniques. Therefore, they fall short in examining spatiotemporally complex gait characteristics including interactions across multiple segments and joints. MethodsTreadmill walking data from ten healthy older adults and ten individuals with idiopathic Parkinson's disease were collected at their self-selected speed. Additionally treadmill walking data from previously collected gait studies on 20 young adults were also used. This study utilized new gait assessment techniques that quantitatively examined joint coupling characteristics (via Condition Signature Analysis), variability and complexity of joint variables (via Phase Portrait Analysis), and movement asymmetry (via Regions of Deviation analysis) of the three different groups. FindingsPeople with Parkinson's disease had the highest asymmetry among the three groups. Aging and Parkinson's disease significantly decreased complexity of hip and ankle joint movements, respectively, while there were no significant differences in variability measures among the three groups. The Condition Signature Analysis method suggested significant differences of joint coupling patterns due to aging and Parkinson's disease. InterpretationThese new gait assessment techniques successfully captured changes in asymmetry, variability, complexity, and joint coupling patterns. Quantitative gait assessment using these tools can be used to detect various types of gait impairments.