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The monitoring of athletes is crucial to preventing injuries, identifying fatigue or supporting return-to-play decisions. The purpose of this study was to explore the ability of Kohonen neural network self-organizing maps (SOM) to objectively characterize movement patterns during sidestepping and their association with injury risk. Further, the network's sensitivity to detect limb dominance was assessed. The data of 67 athletes with a total of 613 trials were included in this study. The 3D trajectories of 28 lower-body passive markers collected during sidestepping were used to train a SOM. The network consisted of 1247 neurons distributed over a 43 × 29 rectangular map with a hexagonal neighbourhood topology. Out of 61,913 input vectors, the SOM identified 1247 unique body postures. Visualizing the movement trajectories and adding several hidden variables allows for the investigation of different movement patterns and their association with joint loading. The used approach identified athletes that show significantly different movement strategies when sidestepping with their dominant or non-dominant leg, where one strategy was clearly associated with ACL-injury-relevant risk factors. The results highlight the ability of unsupervised machine learning to monitor an individual athlete's status without the necessity to reduce the complexity of the data describing the movement.

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BACKGROUND: Hallux valgus (HV) is a gait-altering orthopedic deformity, somewhat more prevalent in women, which often affects both limbs. Although surgery is a commonly applied treatment, there is no consensus in the literature on how invasive HV correction affects spatiotemporal gait parameters, or how quickly improvement can be expected. We investigated gait parameters in female HV patients who underwent bilateral surgical correction of hallux valgus, both preoperatively and 18 weeks following surgery (a timeframe relevant from the perspective of physical therapy), and also in relation to a non-HV control group. METHODS: A total of 23 women aged 40-70 years, with moderate to severe HV deformity in both feet, were assessed preoperatively and 18 weeks postoperatively, and an age-matched control group of 76 healthy women was also assessed. A total of 22 spatiotemporal parameters were collected during 30 s walks over an electronic walkway (Zebris Medical System). RESULTS: Of the 22 parameters analyzed, significant differences between the preoperative experimental and control groups were found only in 4 parameters (Velocity, Right step time, Total double support and Stride time), but in 16 parameters between the postoperative experimental and control groups (the greatest impact being found for: Left and Right Step time, Stride time, Cadence, Right Foot rotation, Left Step length (%leg length) and Stride length (%leg length)). CONCLUSIONS: Women after bilateral HV correction did not exhibit improved (i.e., more normal) gait parameters at 18 weeks postoperatively; rather, they showed more gait abnormalities than preoperatively. These findings urge longer-term planning of postoperative rehabilitation, involving continual evaluation of gait improvement.

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Aim: Stretching is often used to increase/maintain muscle length and improve joint range of motion (ROM) in children with cerebral palsy (CP). However, outcomes at the muscle (remodeling) and resulting function appear to be highly variable and often unsatisfactory. During passive joint rotation, the Achilles tendon lengthens more than the in-series medial gastrocnemius muscle in children with CP, which might explain the limited effectiveness of stretching interventions. We aimed to ascertain whether increasing tendon stiffness, by performing resistance training, improves the effectiveness of passive stretching, indicated by an increase in medial gastrocnemius fascicle length. Methods: Sixteen children with CP (Age median [IQR]: 9.6 [8.6, 10.5]) completed the study. Children were randomly assigned to a combined intervention of stretching and strengthening of the calf muscles (n = 9) or a control (stretching-only) group (n = 7). Medial gastrocnemius fascicle length at a resting ankle angle, lengthening during passive joint rotations, and tendon stiffness were assessed by combining dynamometry and ultrasound imaging. The study was registered on clinicaltrials.gov (NCT02766491). Results: Resting fascicle length and tendon stiffness increased more in the intervention group compared to the control group (median [95% CI] increase fascicle length: 2.2 [1.3, 4.3] mm; stiffness: 13.6 [9.9, 17.7] N/mm) Maximum dorsiflexion angle increased equally in both groups. Conclusion: This study provides proof of principle that a combined resistance and stretching intervention can increase tendon stiffness and muscle fascicle length in children with CP. This demonstrates that remodeling of muscle structure is possible with non-invasive interventions in spastic CP.

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Stretch reflex hyperactivity in the gastrocnemius of children with spastic cerebral palsy (CP) is commonly evaluated by passively rotating the ankle joint into dorsiflexion at different velocities, such as applied in conventional clinical spasticity assessments. However, surface electromyography (sEMG) collected from the medial gastrocnemius (MG) during such examination reveals unexplained heterogeneity in muscle activation between patients. Recent literature also highlights altered muscle tensile behavior in children with spastic CP. We aimed to document MG muscle and tendon lengthening during passive ankle motion at slow and fast velocity and explore its interdependence with the elicited hyperactive stretch reflex. The ankle of 15 children with CP (11 ± 3 years, GMFCS 9I 6II, 8 bilateral, 7 unilateral) and 16 typically developing children (TDC) was passively rotated over its full range of motion at slow and fast velocity. Ultrasound, synchronized with motion-analysis, was used to track the movement of the MG muscle-tendon junction and extract the relative lengthening of muscle and tendon during joint rotation. Simultaneously, MG sEMG was measured. Outcome parameters included the angular and muscle lengthening velocities 30 ms before EMG onset and the gain in root mean square EMG during stretch, as a measure of stretch reflex activity. Compared to slow rotation, the muscle lengthened less and stretch reflex activity was higher during fast rotation. These velocity-induced changes were more marked in CP compared to TDC. In the CP group, muscle-lengthening velocity had higher correlation coefficients with stretch reflex hyperactivity than joint angular velocity. Muscles with greater relative muscle lengthening during slow rotation had earlier and stronger stretch reflexes during fast rotation. These initial results suggest that ankle angular velocity is not representative of MG muscle lengthening velocity and is less related to stretch reflex hyperactivity than MG muscle lengthening. In addition, muscles that lengthened more during slow joint rotation were more likely to show a velocity-dependent stretch reflex. This interdependence of muscle lengthening and stretch reflexes may be important to consider when administering treatment. However, muscle and tendon lengthening properties alone could not fully explain the variability in stretch reflexes, indicating that other factors should also be investigated.

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NEW FINDINGS: What is the central question of this study? Which structures of the medial gastrocnemius muscle-tendon unit contribute to its lengthening during joint rotation and thus receive the stretching stimulus? What is the main finding and its importance? We show, for the first time, that muscle and tendon lengthen in a different manner in children with cerebral palsy compared with typically developing children during a similar amount of muscle-tendon unit lengthening or joint rotation. This indicates possible differences in mechanical muscle and tendon properties attributable to cerebral palsy, which are not evident by assessment of muscle function at the level of a joint. ABSTRACT: Children with cerebral palsy (CP) commonly present with reduced ankle range of motion (ROM) attributable, in part, to changes in mechanical properties of the muscle-tendon unit (MTU). Detailed information about how muscle and tendon interact to contribute to joint rotation is currently lacking but might provide essential information to explain the limited effectiveness of stretching interventions in children with CP. The purpose of this study was to quantify which structures contribute to MTU lengthening and thus receive the stretch during passive ankle joint rotation. Fifteen children with CP (age, in mean ± SD, 11.4 ± 3 years) and 16 typically developing (TD) children (age, in mean ± SD, 10.2 ± 3 years) participated. Ultrasound was combined with motion tracking, joint torque and EMG to record fascicle, muscle and tendon lengthening of the medial gastrocnemius during passive ankle joint rotations over the full ROM and a common ROM. In children with CP, relative to MTU lengthening, muscle and fascicles lengthened less (CP, 50.4% of MTU lengthening; TD, 63% of MTU lengthening; P < 0.04) and tendon lengthened more (CP, 49.6% of MTU lengthening; TD, 37% of MTU lengthening; P < 0.01) regardless of the ROM studied. Differences between groups in the amount of lengthening of the underlying structures during a similar amount of joint rotation and MTU displacement indicate possible differences in tissue mechanical properties attributable to CP, which are not evident by assessment at the level of a joint. These factors should be considered when assessing and treating muscle function in children with CP, for example during stretching exercises, because the muscle might not receive much of the applied lengthening stimulus.

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NEW FINDINGS: What is the central question of this study? Can the increased range of motion seen acutely after stretching in children with cerebral palsy be explained by changes in the stiffness of the medial gastrocnemius fascicles? What is the main finding and its importance? We show, for the first time, that passive muscle and tendon properties are not changed acutely after a single bout of stretching in children with cerebral palsy and, therefore, do not contribute to the increase in range of motion. This contradicts common belief and what happens in healthy adults. ABSTRACT: Stretching is often used to increase or maintain the joint range of motion (ROM) in children with cerebral palsy (CP), but the effectiveness of these interventions is limited. Therefore, our aim was to determine the acute changes in muscle-tendon lengthening properties that contribute to increased ROM after a bout of stretching in children with CP. Eleven children with spastic CP [age 12.1 (3 SD) years, 5/6 hemiplegia/diplegia, 7/4 gross motor function classification system level I/II] participated. Each child received three sets of five × 20 s passive, manual static dorsiflexion stretches separated by 30 s rest, with 60 s rest between sets. Before and immediately after stretching, ultrasound was used to measure medial gastrocnemius fascicle lengthening continuously over the full ROM and an individual common ROM pre- to post-stretching. Simultaneously, three-dimensional motion of two marker clusters on the shank and the foot was captured to calculate ankle angle, and ankle joint torque was calculated from manually applied torques and forces on a six degrees-of-freedom load cell. After stretching, the ROM was increased [by 9.9 (12.0) deg, P = 0.005]. Over a ROM common to both pre- and post-measurements, there were no changes in fascicle lengthening or torque. The maximal ankle joint torque tolerated by the participants increased [by 2.9 (2.4) N m, P = 0.003], and at this highest passive torque the maximal fascicle length was 2.8 (2.4) mm greater (P = 0.009) when compared with before stretching. These results indicate that the stiffness of the muscle fascicles in children with CP remains unaltered by an acute bout of stretching.

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When studying muscle and whole-body function in children with cerebral palsy (CP), knowledge about both internal and external moment arms is essential since they determine the mechanical advantage of a muscle over an external force. Here we asked if Achilles tendon moment arm (MAAT) length is different in children with CP and age-matched typically developing (TD) children, and if MAAT can be predicted from anthropometric measurements. Sixteen children with CP (age: 10y 7m±3y, 7 hemiplegia, 12 diplegia, GMFCS level: I (11) and II (8)) and twenty TD children (age: 10y 6m±3y) participated in this case-control study. MAAT was calculated at 20° plantarflexion by differentiating calcaneus displacement with respect to ankle angle. Seven anthropometric variables were measured and related to MAAT. We found normalized MAAT to be 15% (∼7mm) smaller in children with CP compared to TD children (p=0.003). MAAT could be predicted by all anthropometric measurements with tibia length explaining 79% and 72% of variance in children with CP and TD children, respectively. Our findings have important implications for clinical decision making since MAAT influences the mechanical advantage about the ankle, which contributes to movement function and is manipulated surgically.

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OBJECTIVE: To illustrate and discuss sources of gait deviations (experimental, genuine and intentional) during a gait analysis and how these deviations inform clinical decision making. METHODS: A case study of a 24-year old male diagnosed with Alkaptonuria undergoing a routine gait analysis. A 3D motion capture with the Helen-Hayes marker set was used to quantify lower-limb joint kinematics during barefoot walking along a 10m walkway at a self-selected pace. Additional 2D video data were recorded in the sagittal and frontal plane. The patient reported no aches or pains in any joint and described his lifestyle as active. RESULTS: Temporal-spatial parameters were within normal ranges for his age and sex. Three sources of gait deviations were identified; the posteriorly rotated pelvis was due to an experimental error and marker misplacement, the increased rotation of the pelvis in the horizontal plane was genuine and observed in both 3D gait curves and in 2D video analysis, finally the inconsistency in knee flexion/extension combined with a seemingly innocuous interest in the consequences of abnormal gait suggested an intentional gait deviation. CONCLUSIONS: Gait analysis is an important analytical tool in the management of a variety of conditions that negatively impact on movement. Experienced gait analysts have the ability to recognise genuine gait adaptations that forms part of the decision-making process for that patient. However, their role also necessitates the ability to identify and correct for experimental errors and critically evaluate when a deviation may not be genuine.

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Alkaptonuria is a rare metabolic disease leading to systemic changes including early and severe arthropathy which affects mobility. For unknown reasons, the onset of degenerative changes is delayed to around 30 years of age when both objective and subjective symptoms develop. In order to complement description of the structural changes in alkaptonuria with measures of movement function, clinical gait analysis was added to the list of assessments in 2013. The aim of this study was to describe the deviation of gait from normality as a function of age in patients with alkaptonuria. Three-dimensional movement of reflective markers attached to joints were captured during walking in 39 patients and 10 controls. Subsequent to processing the data to emphasise the shape of marker trajectories, the mean Movement Deviation Profile was generated for all participants. This single number measure gives the deviation of a patient's gait from a distributed definition of gait normality. Results showed that gait deviation roughly follows a sigmoid profile with minimal increase of gait deviations in a younger patient group and an abrupt large increase around the second half of the 4th decade of life. Larger variations of gait deviations were found in the older group than in the younger group suggesting a complex interaction of multiple factors which determine gait function after symptoms manifest. Continued gait analysis of adults with AKU, extended to younger adults and children with AKU, is expected to complete understanding of both the natural history of alkaptonuria and how interventions can affect movement function.

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The ability of the Movement Deviation Profile (MDP) and Gait Deviation Index (GDI) to detect gait changes was compared in a child with cerebral palsy who underwent game training. Conventional gait analysis showed that sagittal plane angles became mirrored about normality after training. Despite considerable gait changes, the GDI showed minimal change, while the MDP detected a difference equal to a shift between 10-9 on the Functional Assessment Questionnaire scale. Responses of the GDI and MDP were examined during a synthetic transition of the patient's curves from before intervention to a state mirrored about normality. The GDI showed a symmetric response on the two opposite sides of normality but the neural network based MDP gave an asymmetric response reflecting faithfully the unequal biomechanical consequences of joint angle changes. In conclusion, the MDP can detect altered gait even if the changes are missed by the GDI.

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BACKGROUND: Upper limb motor control in fast, goal-directed aiming is altered in tetraplegics following posterior-deltoid musculotendinous transfer. Specifically, movements have similar end-point accuracy but longer duration and lower peak velocity than those of age-matched, neurotypical controls. Here, we examine in detail the interplay between primary movement and submovement phases in five C6 tetraplegic and five control participants. METHODS: Aiming movements were performed in two directions (20 cm away or toward), with or without vision. Trials that contained a submovement phase (i.e., discontinuity in velocity, acceleration or jerk) were identified. Discrete kinematic variables were then extracted on the primary and submovements phases. RESULTS: The presence of submovements did not differ between the tetraplegic (68%) and control (57%) groups, and almost all submovements resulted from acceleration and jerk discontinuities. Tetraplegics tended to make a smaller amplitude primary movement, which had lower peak velocity and greater spatial variability at peak velocity. This was followed by a larger amplitude and longer duration secondary submovement. Peak velocity of primary movement was not related to submovement incidence. Together, the primary and submovement phases of both groups were equally effective in reducing end-point error. CONCLUSIONS: C6 tetraplegic participants exhibit some subtle differences in measures of motor behaviour compared to control participants, but importantly feedforward and feedback processes work effectively in combination to achieve accurate goal-directed aiming.

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BACKGROUND: A mirror placed in the mid-sagittal plane of the body has been used to reduce phantom limb pain and improve movement function in medical conditions characterised by asymmetrical movement control. The mirrored illusion of unimpaired limb movement during gait might enhance the effect, but a physical mirror is only capable of showing parallel movement of limbs in real time typically while sitting. We aimed to overcome the limitations of physical mirrors by developing and evaluating a Virtual Mirror Box which delays the mirrored image of limbs during gait to ensure temporal congruency with the impaired physical limb. METHODS: An application was developed in the CAREN system's D-Flow software which mirrors selected limbs recorded by real-time motion capture to the contralateral side. To achieve phase shifted movement of limbs during gait, the mirrored virtual limbs are also delayed by a continuously calculated amount derived from past gait events. In order to accommodate non-normal proportions and offsets of pathological gait, the movements are morphed so that the physical and virtual contact events match on the mirrored side. Our method was tested with a trans-femoral amputee walking on a treadmill using his artificial limb. Joint angles of the elbow and knee were compared between the intact and mirrored side using cross correlation, root mean squared difference and correlation coefficients. RESULTS: The time delayed adaptive virtual mirror box produced a symmetrical looking gait of the avatar coupled with a reduction of the difference between the intact and virtual knee and elbow angles (10.86° and 5.34° reduced to 4.99° and 2.54° respectively). Dynamic morphing of the delay caused a non-significant change of toe-off events when compared to delaying by 50% of the previous gait cycle, as opposed to the initial contact events which showed a practically negligible but statistically significant increase (p < 0.05). CONCLUSIONS: Adding an adaptive time delay to the Virtual Mirror Box has extended its use to treadmill gait, for the first time. Dynamic morphing resulted in a compromise between mirrored movement of the intact side and gait events of the virtual limbs matched with physical events of the impaired side. Asymmetrical but repeatable gait is expected to provide even more faithful mirroring.

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BACKGROUND: Good control of trunk and pelvic movements is necessary for well controlled leg movements required to perform activities of daily living. The nature of movement coupling between the trunk and pelvis varies and depends on the type of activity. Children with cerebral palsy often have reduced ability to modulate coupling between the trunk and pelvis but movement patterns of the pelvis can be improved by training. The aim of this study was to examine how pelvis to trunk coupling changed while playing a computer game driven by pelvic rotations. METHODS: One boy with cerebral palsy diplegia played the Goblin Post Office game on the CAREN virtual rehabilitation system for six weeks. He navigated a flying dragon in a virtual cave towards randomly appearing targets by rotating the pelvis around a vertical axis. Motion of the pelvis and trunk was captured in real-time by a Vicon 612 optoelectronic system tracking two clusters of three markers attached to the sacrum and thoracic spine. RESULTS: Convex hull areas calculated from angle-angle plots of pelvic and trunk rotations showed that coupling increased over game training (F1,11 = 7.482, p = 0.019). Reaching to targets far from the midline required tighter coupling than reaching near targets (F1,12 = 10.619, p = 0.007). CONCLUSIONS: Increasing coupling appears to be an initial compensation mechanism using the better controlled trunk to drive rotation of the pelvis. Co-contractions causing increased coupling are expected to reduce over longer exposure to training. The control scheme of the training game can be set to facilitate de-coupling of pelvic movements from the trunk. Using large ranges of pelvic rotation required more coupling suggesting that training of selective pelvic movements is likely to be more effective close to a neutral pelvic posture.

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We introduce the Movement Deviation Profile (MDP), which is a single curve showing the deviation of an individual's movement from normality. Joint angles, recorded from typically developing children over one gait cycle, were used to train a self-organizing map (SOM) which then generated MDP curves for patients with gait problems. The mean MDP over the gait cycle showed a high correlation (r(2) = .927) with the Gait Deviation Index (GDI), a statistically significant difference between groups of patients with a range of functional levels (Gillette Functional Assessment Questionnaire Walking Scale 7-10) and a trend of increasing values for patients with cerebral palsy through hemiplegia I-IV, diplegia, triplegia, and quadriplegia. The small difference between the MDP and GDI can be explained by the SOM's method of operation comparing biomechanical patterns to the nearest abstract reference pattern, and its flexibility to compensate for temporal shifts in movement data. The MDP is an alternative method of processing complex biomechanical data, potentially supporting clinical interpretation. The electronic addendum accompanying this article is a standalone program, which can be used to calculate the MDP from gait data, and can also be used in other applications where the deviation of multi-channel temporal data from a reference is required.

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The aim of this study was to determine the influence of punch type (Jab, Cross, Lead Hook and Reverse Hook) and punch modality (Single maximal, 'In-synch' and 'Out of synch' combination) on punch speed and delivery time. Ten competition-standard volunteers performed punches with markers placed on their anatomical landmarks for 3D motion capture with an eight-camera optoelectronic system. Speed and duration between key moments were computed. There were significant differences in contact speed between punch types (F(2,18,84.87) = 105.76, p = 0.001) with Lead and Reverse Hooks developing greater speed than Jab and Cross. There were significant differences in contact speed between punch modalities (F(2,64,102.87) = 23.52, p = 0.001) with the Single maximal (M+/- SD: 9.26 +/- 2.09 m/s) higher than 'Out of synch' (7.49 +/- 2.32 m/s), 'In-synch' left (8.01 +/- 2.35 m/s) or right lead (7.97 +/- 2.53 m/s). Delivery times were significantly lower for Jab and Cross than Hook. Times were significantly lower 'In-synch' than a Single maximal or 'Out of synch' combination mode. It is concluded that a defender may have more evasion-time than previously reported. This research could be of use to performers and coaches when considering training preparations.

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Cervical spinal lesions at C6 result in paralysis of the triceps brachii while leaving deltoid and elbow flexor function intact. We examined the spatial-temporal characteristics of goal-directed aiming movements performed by C6 tetraplegics who had undergone musculotendinous transfer surgery in which the posterior deltoid replaces the triceps as the elbow extensor. On some trials, liquid crystal goggles were used to eliminate vision of the limb and target upon movement initiation. Although tetraplegic participants achieved the same degree of movement accuracy/consistency as control participants, their movement times were longer regardless of whether the movements were made away from (elbow extension) or towards the body (elbow flexion). Longer movement times were related to lower peak velocities, and not the symmetry of the aiming profiles. The tetraplegic participants were no more dependent on visual feedback for limb regulation than control participants. Although the characteristics of the movement trajectories were surprisingly similar, in both vision conditions, tetraplegics required more real and proportional time to reduce spatial variability in the limb's trajectory for elbow extensions. Our results indicate that the sensorimotor system is adaptable and that the representations governing limb control are not muscle specific.

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The functionality of movable platforms used in human balance studies is limited as they allow rotations around pre-defined axes, which typically run close to the platform's surface and so cannot be used to directly investigate control mechanisms of proximal joints. A new six degrees of freedom platform (CAREN, Motek, Amsterdam) is now available which in principle could be programmed to rotate around any axis of rotation. The location of the default axes of rotation for this device are not documented and the algorithm to move the axes has not yet been defined. The purpose of this study was to (1) locate the platform's default axes of rotation, (2) implement an algorithm for relocating its axes of rotation and (3) evaluate the algorithm. A simplified method was developed to locate the bounding rectangles within which the default axes of rotations were located. The three axes of rotation were found to be at x=1.13+/-0.69 mm, z=-204.22+/-0.63 mm in the roll plane, y=-2.67+/-0.59 mm, z=-211.38+/-0.63 mm in the pitch plane and x=0.43+/-0.70 mm, y=-4.72+/-0.65 mm in the yaw plane (X: left, Y: rear, Z: up), relative to the centre of its surface, with the maximum bounding rectangle of dimensions 2.50mm by 2.42 mm. Relocation of the platform's axes of rotation was achieved by the use of compensatory corrections, which were determined using a translation algorithm. Evaluation of the algorithm involved pitching the platform around three newly defined axes in the sagittal plane, representing the ankle, knee and hip joints. The platform was able to rotate around the new axes while keeping the instantaneous axes of rotation within bounding rectangles of 1.87 mm x 0.81 mm (ankle), 3.04 mm x 1.23 mm (knee), 3.14 mm x 1.63 mm (hip). The ability to overcome the limitation of other moveable platforms makes the CAREN system a valuable tool in research on the role of individual joints in balance.

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