Medial gastrocnemius and soleus muscle-tendon unit, fascicle, and tendon interaction during walking in children with cerebral palsy

Synergistic effects of MFG-E8 and whey protein on mitigating d-galactose-induced sarcopenia through PI3K/AKT/PGC-1α and MAPK/ERK signaling pathways

Milk fat globule epidermal growth factor 8 (MFG-E8) and whey protein have emerged as promising bionutrient supplements for enhancing skeletal muscle mass and function. In the present study, aging-related sarcopenia rat model was employed to elucidate the effects of the combined administration of MFG-E8 and whey protein on the catabolism and anabolism of gastrocnemius protein. Combined intervention led to notable enhancements in the antioxidative stress status and mitochondrial biogenesis capacity of gastrocnemius muscle fibers in the aging rats, concomitant with a significant inhibition of lipid accumulation. Moreover, the synergistic effect of MFG-E8 and whey protein was found to exert modulatory effects on key signaling pathways, including PI3K/Akt/PGC-1α pathway and MAPK/ERK signaling pathways in the gastrocnemius muscle of the aging rats. Specifically, this combined intervention was observed to promote mitochondrial biogenesis and regulate the expression of protein anabolism and catabolism-related regulators, thereby facilitating the alleviation of mitochondrial oxidative stress and enhancing biogenesis in gastrocnemius tissues. The findings of our study provide compelling evidence for the potential of MFG-E8 as a promising dietary supplement with antisarcopenic properties to ameliorate muscle protein metabolism disorders and mitigate mitochondrial-mediated myoblast apoptosis induced by oxidative stress.

ISB clinical biomechanics award winner 2023: Medial gastrocnemius muscle and Achilles tendon interplay during gait in cerebral palsy

BACKGROUND

The interplay between the medial gastrocnemius muscle and the Achilles tendon is crucial for efficient walking. In cerebral palsy, muscle and tendon remodelling alters the role of contractile and elastic components. The aim was to investigate the length changes of medial gastrocnemius belly and fascicles, and Achilles tendon to understand their interplay to gait propulsion in individuals with cerebral palsy.

METHODS

Twelve young individuals with cerebral palsy and 12 typically developed peers were assessed during multiple gait cycles using 3D gait analysis combined with a portable ultrasound device. By mapping ultrasound image locations into the shank reference frame, the medial gastrocnemius belly, fascicle, and Achilles tendon lengths were estimated throughout the gait cycle. Participants with cerebral palsy were classified into equinus and non-equinus groups based on their sagittal ankle kinematics.

FINDINGS

In typically developed participants, the Achilles tendon undertook most of the muscle-tendon unit lengthening during stance, whereas in individuals with cerebral palsy, this lengthening was shared between the medial gastrocnemius belly and Achilles tendon, which was more evident in the equinus group. The lengthening behaviour of the medial gastrocnemius fascicles resembled that of the Achilles tendon in cerebral palsy.

INTERPRETATION

The findings revealed similar length changes of the medial gastrocnemius fascicles and Achilles tendon, highlighting the enhanced role of the muscle in absorbing energy during stance in cerebral palsy. These results, together with the current knowledge of increased intramuscular stiffness, suggest the exploitation of intramuscular passive forces for such energy absorption.

Comparative validation of two patient-specific modelling pipelines for predicting knee joint forces during level walking

Over the past few years, the use of computer models and simulations tailored to the patient's physiology to assist clinical decision-making has increased enormously.While several pipelines to develop personalized models exist, their adoption on a large scale is still limited due to the required niche computational skillset and the lengthy operations required. Novel toolboxes, such as STAPLE, promise to streamline and expedite the development of image-based skeletal lower limb models. STAPLE-generated models can be rapidly generated, with minimal user input, and present similar joint kinematics and kinetics compared to models developed employing the established INSIGNEO pipeline. Yet, it is unclear how much the observed discrepancies scale up and affect joint contact force predictions. In this study, we compared image-based musculoskeletal models developed (i) with the INSIGNEO pipeline and (ii) with a semi-automated pipeline that combines STAPLE and nmsBuilder, and assessed their accuracy against experimental implant data.Our results showed that both pipelines predicted similar total knee joint contact forces between one another in terms of profiles and average values, characterized by a moderately high level of agreement with the experimental data. Nonetheless, the Student t-test revealed statistically significant differences between both pipelines. Of note, the STAPLE-based pipeline required considerably less time than the INSIGNEO pipeline to generate a musculoskeletal model (i.e., 60 vs 160 min). This is likely to open up opportunities for the use of personalized musculoskeletal models in clinical practice, where time is of the essence.

In vivo imaging of skeletal muscle form and function: 50 years of insight

Skeletal muscle form and function has fascinated scientists for centuries. Our understanding of muscle function has long been driven by advancements in imaging techniques. For example, the sliding filament theory of muscle, which is now widely leveraged in biomechanics research, stemmed from observations made possible by scanning electron microscopy. Over the last 50 years, advancing in medical imaging, combined with ingenuity and creativity of biomechanists, have provide a wealth of new and important insights into in vivo human muscle function. Incorporation of in vivo imaging has also advanced computational modeling and allowed our research to have an impact in many clinical populations. While this review does not provide a comprehensive or meta-analysis of the all the in vivo muscle imaging work over the last five decades, it provides a narrative about the past, present, and future of in vivo muscle imaging.

The influence of wearing an ultrasound device on gait in children with cerebral palsy and typically developing children

BACKGROUND

Ultrasonography with motion analysis enables dynamic imaging of medial gastrocnemius (MG) muscles and tendons during gait. This revealed pathological muscle-tendon dynamics in children with spastic cerebral palsy (CP) compared to typically developing (TD) children. However, wearing an ultrasound probe on the lower leg could interfere with gait and bias muscle length changes observed with ultrasound.

RESEARCH QUESTION

Does wearing an ultrasound probe on the MG influence gait in children with CP and TD children?

METHODS

Eighteen children with spastic CP and 16 age-matched TD children walked at comfortable walking speed on an instrumented treadmill. One baseline gait condition (BASE) and two conditions with an ultrasound probe and custom-made probe holder were measured: on the mid-muscle fascicles (FAS) and on the muscle-tendon junction (MTJ). The effect of condition and group on spatiotemporal parameters, hip, knee and ankle kinematics, ankle moment, ankle power, and modeled MG muscle-tendon unit (MTU) length was assessed using two-way repeated measures ANOVA's. Statistical non-parametric mapping was applied for time-series. Post-hoc paired-samples t-tests were conducted, and the root mean square difference was calculated for significant parts.

RESULTS

Children took wider steps during FAS (CP, TD) and MTJ (TD) compared to BASE, and during FAS compared to MTJ (CP). Hip extension was lower (2.7°) during terminal stance for MTJ compared to FAS for TD only. There was less swing knee flexion (FAS 4.9°; MTJ 4.0°) and ankle plantarflexion around toe-off (FAS 3.0°; MTJ 2.4°) for both ultrasound placements, with no group effect. Power absorption during loading response was slightly increased for both ultrasound placements (0.12 W/kg), with no group effect. MTU shortened less in swing for both ultrasound placements (FAS 3.6 mm; MTJ 3.7 mm), with no group effect.

SIGNIFICANCE

Wearing an ultrasound probe causes minimal lower-limb gait alterations and MTU length changes that are mostly similar in CP and TD.

Electromyographic biofeedback-driven gaming to alter calf muscle activation during gait in children with spastic cerebral palsy

BACKGROUND

Children with cerebral palsy often show deviating calf muscle activation patterns during gait, with excess activation during early stance and insufficient activation during push-off.

RESEARCH QUESTION

Can children with cerebral palsy improve their calf muscle activation patterns during gait using one session of biofeedback-driven gaming?

METHODS

Eighteen children (6-17 y) with spastic cerebral palsy received implicit game-based biofeedback on electromyographic activity of the calf muscle (soleus or gastrocnemius medialis) while walking on a treadmill during one session. Biofeedback alternately aimed to reduce early stance activity, increase push-off activity, and both combined. Early stance and push-off activity and the double-bump-index (early stance divided by push-off activity) were determined during baseline and walking with feedback. Changes were assessed at group level using repeated measures ANOVA with simple contrast or Friedman test with post-hoc Wilcoxon signed rank test, as well as individually using independent t-tests or Wilcoxon rank sum tests. Perceived competence and interest-enjoyment were assessed through a questionnaire.

RESULTS

Children successfully decreased their electromyographic activity during early stance feedback trials (relative decrease of 6.8 ± 12.2 %, P = 0.025), with a trend during the combined feedback trials (6.5 ± 13.9 %, P = 0.055), and increased their electromyographic activity during push-off feedback trials (8.1 ± 15.8 %, P = 0.038). Individual improvements were seen in twelve of eighteen participants. All children experienced high levels of interest-enjoyment (8.4/10) and perceived competence (8.1/10).

SIGNIFICANCE

This exploratory study suggests that children with cerebral palsy can achieve small within-session improvements of their calf muscle activation pattern when provided with implicit biofeedback-driven gaming in an enjoyable manner. Follow-up gait training studies can incorporate this method to assess retention and long-term functional benefits of electromyographic biofeedback-driven gaming.

A comprehensive normative reference database of muscle morphology in typically developing children aged 3-18 years-a cross-sectional ultrasound study

During childhood, muscle growth is stimulated by a gradual increase in bone length and body mass, as well as by other factors, such as physical activity, nutrition, metabolic, hormonal, and genetic factors. Muscle characteristics, such as muscle volume, anatomical cross-sectional area, and muscle belly length, need to continuously adapt to meet the daily functional demands. Pediatric neurological and neuromuscular disorders, like cerebral palsy and Duchenne muscular dystrophy, are characterized by impaired muscle growth, which requires treatment and close follow-up. Nowadays ultrasonography is a commonly used technique to evaluate muscle morphology in both pediatric pathologies and typically developing children, as it is a quick, easy applicable, and painless method. However, large normative datasets including different muscles and a large age range are lacking, making it challenging to monitor muscle over time and estimate the level of pathology. Moreover, in order to compare individuals with different body sizes as a result of age differences or pathology, muscle morphology is often normalized to body size. Yet, the usefulness and practicality of different normalization techniques are still unknown, and clear recommendations for normalization are lacking. In this cross-sectional cohort study, muscle morphology of four lower limb muscles (medial gastrocnemius, tibialis anterior, the distal compartment of the semitendinosus, rectus femoris) was assessed by 3D-freehand ultrasound in 118 typically developing children (mean age 10.35 ± 4.49 years) between 3 and 18 years of age. The development of muscle morphology was studied over the full age range, as well as separately for the pre-pubertal (3-10 years) and pubertal (11-18 years) cohorts. The assumptions of a simple linear regression were checked. If these assumptions were fulfilled, the cross-sectional growth curves were described by a simple linear regression equation. Additional ANCOVA analyses were performed to evaluate muscle- or gender-specific differences in muscle development. Furthermore, different scaling methods, to normalize muscle morphology parameters, were explored. The most appropriate scaling method was selected based on the smallest slope of the morphology parameter with respect to age, with a non-significant correlation coefficient. Additionally, correlation coefficients were compared by a Steiger's Z-test to identify the most efficient scaling technique. The current results revealed that it is valid to describe muscle volume (with exception of the rectus femoris muscle) and muscle belly length alterations over age by a simple linear regression equation till the age of 11 years. Normalizing muscle morphology data by allometric scaling was found to be most useful for comparing muscle volumes of different pediatric populations. For muscle lengths, normalization can be achieved by either allometric and ratio scaling. This study provides a unique normative database of four lower limb muscles in typically developing children between the age of 3 and 18 years. These data can be used as a reference database for pediatric populations and may also serve as a reference frame to better understand both physiological and pathological muscle development.

Motor performance, motor impairments, and quality of life after eccentric resistance training in neurological populations: A systematic review and meta-analyses

BACKGROUND

Many overlapping factors impair motor performance and quality of life in neurological patients. Eccentric resistance training (ET) has potential benefits for improving motor performance and treating motor impairments better than some traditional rehabilitation approaches.

OBJECTIVE

To estimate the effect of ET in neurological settings.

METHODS

Seven databases were reviewed up to May 2022 according to PRSIMA guidelines to find randomized clinical trials involving adults with a neurological condition, who underwent ET as set by the American College of Sports Medicine. Motor performance (main outcome) was assessed as strength, power and capacities during activity. Secondary outcomes (impairments) were muscle structure, flexibility, muscle activity, tone, tremor, balance and fatigue. Tertiary outcomes were risk of fall, and self-reports of quality of life.

RESULTS

Ten trials were included, assessed using Risk of Bias 2.0 tool, and used to compute meta-analyses. Effective effects in favour of ET were found for strength and power, but not for capacities during activity. Mixed results were found for secondary and tertiary outcomes.

CONCLUSION

ET may be a promising intervention to better improve strength/power in neurological patients. More studies are needed to improve the quality of evidence underlying changes responsible for these results.

Under pressure: design and validation of a pressure-sensitive insole for ankle plantar flexion biofeedback during neuromuscular gait training

BACKGROUND

Electromyography (EMG)-based audiovisual biofeedback systems, developed and tested in research settings to train neuromuscular control in patient populations such as cerebral palsy (CP), have inherent implementation obstacles that may limit their translation to clinical practice. The purpose of this study was to design and validate an alternative, plantar pressure-based biofeedback system for improving ankle plantar flexor recruitment during walking in individuals with CP.

METHODS

Eight individuals with CP (11-18 years old) were recruited to test both an EMG-based and a plantar pressure-based biofeedback system while walking. Ankle plantar flexor muscle recruitment, co-contraction at the ankle, and lower limb kinematics were compared between the two systems and relative to baseline walking.

RESULTS

Relative to baseline walking, both biofeedback systems yielded significant increases in mean soleus (43-58%, p < 0.05), and mean (68-70%, p < 0.05) and peak (71-82%, p < 0.05) medial gastrocnemius activation, with no differences between the two systems and strong relationships for all primary outcome variables (R = 0.89-0.94). Ankle co-contraction significantly increased relative to baseline only with the EMG-based system (52%, p = 0.03).

CONCLUSION

These findings support future research on functional training with this simple, low-cost biofeedback modality.

Use of shear wave elastography to analyze the muscle structure in children with spastic cerebral palsy

PURPOSE

In children with cerebral palsy (CP), gastrocnemius muscle spasticity may lead to pes equinus posture which causes insufficient ankle joint dorsiflexion for normal gait. The aim of this study was to analyze the stiffness of gastrocnemius and tibialis anterior muscles by shear wave elastography (SWE) in children with pes equinus deformity due to spastic CP.

METHODS

24 legs of 12 children (6 females and 6 males, mean age 45.8 months) with CP were prospectively included in the study. Tissue stiffness quantification with shear-wave velocity (SWV) was analyzed.

RESULTS

The mean SWVs of the gastrocnemius and tibialis anterior muscles were 3.91±0.26 m/s and 2.67±0.18 m/s, respectively. The stiffness of the gastrocnemius muscle was significantly higher than the stiffness of the tibialis anterior muscle (p <  0.0001). There was no correlation between the stiffness of these muscles (r = 0.129, p >  0.05).

CONCLUSION

Gastrocnemius muscles were stiffer than tibialis anterior muscles in patients with spastic CP. But stiffness between these muscles was not correlated with each other. Pes equinus may be related to stiff gastrocnemius in these patients. This study demonstrates the clinical potential for SWE as a non-invasive tool for analyzing calf muscle stiffness.

Aberrant movement-related somatosensory cortical activity mediates the extent of the mobility impairments in persons with cerebral palsy

KEY POINTS

Persons with cerebral palsy (CP) have reduced somatosensory cortical responses at rest and during movement. The somatosensory cortical responses during movement mediate the relationship between the somatosensory cortical responses at rest and mobility. Persons with CP may have altered sensorimotor feedback that ultimately contributes to impaired mobility.

ABSTRACT

There are numerous clinical reports that persons with cerebral palsy (CP) have proprioceptive, stereognosis and tactile discrimination deficits. The current consensus is that these altered perceptions are attributable to aberrant somatosensory cortical activity. It has been inferred from these data that persons with CP do not adequately process ongoing sensory feedback during motor actions, which accentuates the extent of their mobility impairments. However, this hypothesis has yet to be directly tested. We used magnetoencephalographic (MEG) brain imaging to address this knowledge gap by quantifying the somatosensory dynamics evoked by applying electrical stimulation to the tibial nerve in 22 persons with CP and 25 neurotypical (NT) controls while at rest and during an ankle plantarflexion isometric force motor task. We also quantified the spatiotemporal gait biomechanics of participants outside the scanner. Consistent with the literature, our results confirmed that the strength of somatosensory cortical activity was weaker in the persons with CP compared to the NT controls. Our results also showed that the strength of the somatosensory cortical responses were significantly weaker during the isometric ankle force task than at rest. Most importantly, our results showed that the strength of somatosensory cortical activity during the ankle plantarflexion force production task mediated the relationship between somatosensory cortical activity at rest and both walking velocity and step length. These results suggest that youth with CP have aberrant somatosensory cortical activity during isometric force generation, which ultimately contributes to the extent of mobility impairments seen in this patient population. Abstract figure legend Magnetoencephalographic brain imaging was used to determine the effect of sensory feedback during movement on mobility in persons with cerebral palsy. Persons with cerebral palsy had reduced somatosensory cortical activity at rest and during movement compared with their neurotypical peers. Further, the somatosensory cortical activity during movement mediated the relationship between somatosensory cortical activity at rest and mobility. These results indicate that difficulties in sensorimotor integration may contribute to the mobility impairments seen in this patient population. This article is protected by copyright. All rights reserved.

Effects of voluntary exercise on muscle structure and function in cerebral palsy

Skeletal muscles are required for functional movement and force production. While it is clear that cerebral palsy (CP) results in loss of muscle strength and bodily function, and that much of this loss is caused by injury to the central nervous system, muscle is a very plastic tissue that is also dramatically affected. In many studies, it is assumed that voluntary exercise will cause the muscle to respond in the same way that typically developing muscle does, but there are scarce data demonstrating that this is true. The purpose of this review is to briefly describe muscle architectural adaptation to various forms of exercise with specific reference to voluntary exercise performed in children with CP. Exercise itself is not generic but can vary by intensity, duration, and the exact nature of the muscle length change and velocity imposed during the exercise. Our goal is to stimulate discussion in this area by pointing out salient experimental variables and, ultimately, to improve activity and participation in children with CP.

A Human-Centered Machine-Learning Approach for Muscle-Tendon Junction Tracking in Ultrasound Images

Biomechanical and clinical gait research observes muscles and tendons in limbs to study their functions and behaviour. Therefore, movements of distinct anatomical landmarks, such as muscle-tendon junctions, are frequently measured. We propose a reliable and time efficient machine-learning approach to track these junctions in ultrasound videos and support clinical biomechanists in gait analysis. In order to facilitate this process, a method based on deep-learning was introduced. We gathered an extensive data set, covering 3 functional movements, 2 muscles, collected on 123 healthy and 38 impaired subjects with 3 different ultrasound systems, and providing a total of 66864 annotated ultrasound images in our network training. Furthermore, we used data collected across independent laboratories and curated by researchers with varying levels of experience. For the evaluation of our method a diverse test-set was selected that is independently verified by four specialists. We show that our model achieves similar performance scores to the four human specialists in identifying the muscle-tendon junction position. Our method provides time-efficient tracking of muscle-tendon junctions, with prediction times of up to 0.078 seconds per frame (approx. 100 times faster than manual labeling). All our codes, trained models and test-set were made publicly available and our model is provided as a free-to-use online service on https://deepmtj.org/.

Typical m. triceps surae morphology and architecture measurement from 0 to 18 years: A narrative review

The aim of this review was to report on the imaging modalities used to assess morphological and architectural properties of the m. triceps surae muscle in typically developing children, and the available reliability analyses. Scopus and MEDLINE (Pubmed) were searched systematically for all original articles published up to September 2020 measuring morphological and architectural properties of the m. triceps surae in typically developing children (18 years or under). Thirty eligible studies were included in this analysis, measuring fibre bundle length (FBL) (n = 11), pennation angle (PA) (n = 10), muscle volume (MV) (n = 16) and physiological cross‐sectional area (PCSA) (n = 4). Three primary imaging modalities were utilised to assess these architectural parameters in vivo: two‐dimensional ultrasound (2DUS; n = 12), three‐dimensional ultrasound (3DUS; n = 9) and magnetic resonance imaging (MRI; n = 6). The mean age of participants ranged from 1.4 years to 18 years old. There was an apparent increase in m. gastrocnemius medialis MV and pCSA with age; however, no trend was evident with FBL or PA. Analysis of correlations of muscle variables with age was limited by a lack of longitudinal data and methodological variations between studies affecting outcomes. Only five studies evaluated the reliability of the methods. Imaging methodologies such as MRI and US may provide valuable insight into the development of skeletal muscle from childhood to adulthood; however, variations in methodological approaches can significantly influence outcomes. Researchers wishing to develop a model of typical muscle development should carry out longitudinal architectural assessment of all muscles comprising the m. triceps surae utilising a consistent approach that minimises confounding errors.

Muscle-tendon unit in children with cerebral palsy

Muscle-tendon unit surgery for correction of deformities and movement dysfunction in children with cerebral palsy (CP) is fairly complicated. An understanding of basic muscle-tendon unit properties and their adaptation to both CP and surgery are important to develop advances in this field. In this review, we provide information to therapists, surgeons, and scientists regarding the short- and long-term adaptations of the muscle-tendon unit. Surgical releases, lengthening, and transpositions are discussed, as are some of the tissue, cellular, and molecular adaptations. What this paper adds Muscle strength, tone, and control must be considered in surgical interventions for cerebral palsy (CP). Muscle-tendon unit lengthening causes significant and lasting weakness requiring prolonged rehabilitation. Sarcomere length increases in CP muscle may be one of the underlying causes of muscle weakness. Muscle satellite cells are decreased and epigenetically modified in a way that may limit muscle growth in CP.

The importance of a consistent workflow to estimate muscle-tendon lengths based on joint angles from the conventional gait model

BACKGROUND

Musculoskeletal models enable us to estimate muscle-tendon length, which has been shown to improve clinical decision-making and outcomes in children with cerebral palsy. Most clinical gait analysis services, however, do not include muscle-tendon length estimation in their clinical routine. This is due, in part, to a lack of knowledge and trust in the musculoskeletal models, and to the complexity involved in the workflow to obtain the muscle-tendon length.

RESEARCH QUESTION

Can the joint angles obtained with the conventional gait model (CGM) be used to generate accurate muscle-tendon length estimates?

METHODS

Three-dimensional motion capture data of 15 children with cerebral palsy and 15 typically developing children were retrospectively analyzed and used to estimate muscle-tendon length with the following four modelling frameworks: (1) 2392-OSM-IK-angles: standard OpenSim workflow including scaling, inverse kinematics and muscle analysis; (2) 2392-OSM-CGM-angle: generic 2392-OpenSim model driven with joint angles from the CGM; (3) modif-OSM-IK-angles: standard OpenSim workflow including inverse kinematics and a modified model with segment coordinate systems and joint degrees-of-freedom similar to the CGM; (4) modif-OSM-CGM-angles: modified model driven with joint angles from the CGM. Joint kinematics and muscle-tendon length were compared between the different modelling frameworks.

RESULTS

Large differences in hip joint kinematics were observed between the CGM and the 2392-OpenSim model. The modif-OSM showed similar kinematics as the CGM. Muscle-tendon length obtained with modif-OSM-IK-angles and modif-OSM-CGM-angles were similar, whereas large differences in some muscle-tendon length were observed between 2392-OSM-IK-angles and 2392-OSM-CGM-angles.

SIGNIFICANCE

The modif-OSM-CGM-angles framework enabled us to estimate muscle-tendon lengths without the need for scaling a musculoskeletal model and running inverse kinematics. Hence, muscle-tendon length estimates can be obtained simply, without the need for the complexity, knowledge and time required for musculoskeletal modeling and associated software. An instruction showing how the framework can be used in a clinical setting is provided on https://github.com/HansUniVie/MuscleLength.

Automated analysis of medial gastrocnemius muscle-tendon junction displacements in heathy young adults during isolated contractions and walking using deep neural networks

BACKGROUND AND OBJECTIVE

Direct measurement of muscle-tendon junction (MTJ) position is important for understanding dynamic tendon behavior and muscle-tendon interaction in healthy and pathological populations. Traditionally, obtaining MTJ position during functional activities is accomplished by manually tracking the position of the MTJ in cine B-mode ultrasound images - a laborious and time-consuming process. Recent advances in deep learning have facilitated the availability of user-friendly open-source software packages for automated tracking. However, these software packages were originally intended for animal pose estimation and have not been widely tested on ultrasound images. Therefore, the purpose of this paper was to evaluate the efficacy of deep neural networks to accurately track medial gastrocnemius MTJ positions in cine B-mode ultrasound images across tasks spanning controlled loading during isolated contractions to physiological loading during treadmill walking.

METHODS

Cine B-mode ultrasound images of the medial gastrocnemius MTJ were collected from 15 subjects (6M/9F, 23 yr, 71.9 kg, 1.8 m) during treadmill walking at 1.25 m/s and during maximal voluntary isometric plantarflexor contractions (MVICs). Five deep neural networks were trained using 480 manually-labeled images collected during walking, defined as the ground truth, and were then used to predict MTJ position in images from novel subjects: 1) during walking (novel-subject) and 2) during MVICs (novel-condition).

RESULTS

We found an average mean absolute error of 1.26±1.30 mm and 2.61±3.31 mm between the ground truth and predicted MTJ positions in the novel-subject and novel-condition evaluations, respectively.

CONCLUSIONS

Our results provide support for the use of open-source software for creating deep neural networks to reliably track MTJ positions in B-mode ultrasound images. We believe this approach to MTJ position tracking is an accessible and time-saving solution, with broad applications for many fields, such as rehabilitation or clinical diagnostics.

Normative Achilles and patellar tendon shear wave speeds and loading patterns during walking in typically developing children

BACKGROUND

Motion analysis is commonly used to evaluate joint kinetics in children with cerebral palsy who exhibit gait disorders. However, one cannot readily infer muscle-tendon forces from joint kinetics. This study investigates the use of shear wave tensiometry to characterize Achilles and patellar tendon forces during gait.

RESEARCH QUESTION

How do Achilles and patellar tendon wave speed and loading modulate with walking speed in typically developing children?

METHODS

Twelve typically developing children (9-16 years old) walked on an instrumented treadmill with shear wave tensiometers over their Achilles (n = 11) and patellar (n = 9) tendons. Wave speeds were recorded at five leg length-normalized walking speeds (very slow to very fast). Achilles and patellar tendon moment arms were measured with synchronized ultrasound and motion capture. The tendon wave speed-load relationship was calibrated at the typical walking speed and used to estimate tendon loading at other walking speeds.

RESULTS

Characteristic Achilles and patellar tendon wave speed trajectories exhibited two peaks over a gait cycle. Peak Achilles tendon force closely aligned with peak ankle plantarflexor moment during pushoff, though force exhibited less modulation with walking speed. A second peak in late swing Achilles loading, which was not evident from the ankle moment, increased significantly with walking speed (p < 0.001). The two peaks in patellar tendon loading occurred at 12 ± 1% and 68 ± 6% of the gait cycle, matching the timing of peak knee extension moment in early stance and early swing. Both patellar tendon load peaks increased significantly with walking speed (p < 0.05).

SIGNIFICANCE

This is the first study to use shear wave tensiometry to characterize Achilles and patellar tendon loading during gait in children. These data could serve as a normative comparison when using tensiometry to identify abnormal tendon loading patterns in individuals who exhibit equinus and/or crouch gait.

Contribution of passive moments to inter-segmental moments during gait: A systematic review

Inter-segmental moments computed by inverse dynamic during gait come from active moments, due to muscle contraction, but also from passive moments, resulting from the resistance of the periarticular structures to their deformation. The evaluation of the proportion of the inter-segmental moments that can be attributed to passive moments has led to divergent results. Thus, the purpose of this study was to systematically search and synthesize the evidence of the contribution of passive moments to inter-segmental moments during healthy and pathological gait. A broad systematic search was performed including four databases. Thirteen studies met all inclusion criteria. Results showed that passive moments participate to inter-segmental moments during gait in a non-negligible way. For the ankle, the evaluation of the proportion of inter-segmental moment attributed to passive structures is 5-20% around the push-off. For the knee, this proportion is 40-98% during late swing and 10-80% during the single support phase. For the hip, it is 20-50% at push-off. For pathological population, it has been shown that this contribution may sometimes be more important, either due to a smaller inter-segmental moment or a larger passive moment. These results suggest that passive mechanisms can contribute substantially to normal human gait, facilitating the propulsion or the braking of the joint. Passive structures, acting as elastic springs, thus help to reduce the energy cost of gait. For pathological gait, studying the contribution of passive moments to inter-segmental moments can help to better understand the aetiology of the pathology.

The effect of musculoskeletal model scaling methods on ankle joint kinematics and muscle force prediction during gait for children with cerebral palsy and equinus gait

Clinical gait analysis incorporated with neuromusculoskeletal modelling could provide valuable information about joint movements and muscle functions during ambulation for children with cerebral palsy (CP). This study investigated how imposing pre-calculated joint angles during musculoskeletal model scaling influence the ankle joint angle and muscle force computation. Ten children with CP and equinus gait underwent clinical gait analysis. For each participant, a "default" (scaled without pre-calculated joint angles) and a "PJA" (scaled with pre-calculated ankle joint angles) model were generated to simulate their gait. Ankle joint angles were calculated with an inverse kinematic (IK) and direct kinematic (DK) approach. Triceps surae and tibialis anterior muscle forces were predicted by static optimisation and EMG-assisted modelling. We found that PJA-derived ankle angles showed a better agreement with what derived from the DK approach. The tibialis anterior muscle prediction was more likely to be affected by the scaling methods for the static optimisation approach and the gastrocnemius muscle force prediction was more likely to be influenced for the EMG-assisted modelling. This study recommends using the PJA model since the good consistency between IK and DK-derived joint angles facilitates communication among different research disciplines.

Dynamic muscle-tendon length following zone 2 calf lengthening surgery in two populations with equinus gait: Idiopathic Toe Walkers and Cerebral Palsy

BACKGROUND

Two populations commonly presenting with equinus gait are Idiopathic Toe-Walkers and children with Cerebral Palsy. Surgical intervention to treat equinus is defined by three zones. Zone three surgery, performed at the Achilles tendon, is most commonly used clinically. There is however, evidence from simulation studies that zone two surgery, performed at the muscle belly, might provide better functional outcomes. The purpose of this study was to investigate the effect of zone two calf-lengthening on post-operative gait in these populations.

METHODS

A retrospective audit of the Queensland Children's Motion Analysis Service database identified 17 toe-walkers (mean age 10.13 (SD 2.625)) and 11 Cerebral Palsy (mean age 9.72 (SD 4.04)) participants that received calf-lengthening surgery for plantarflexion contracture and had pre- and post-surgery 3D gait analysis. Inverse kinematics, dynamics, and muscle analysis were performed in OpenSim (v3.3) using a modified gait2392 model. Pre to post-surgery comparisons were performed in MATLAB using statistical parametric mapping. Dependent variables included ankle kinematics, powers and muscle-tendon length estimates.

FINDINGS

The primary outcome of this study was that ankle dorsiflexion increased in both Idiopathic Toe Walking and Cerebral Palsy groups post-calf lengthening across 90% and 85% of the gait cycle respectively. There was an increase in modelled muscle-tendon lengths, specifically in the medial gastrocnemius, of 78% (toe-walkers), and 100% (Cerebral Palsy) of the gait cycle. Power generation during push-off was not affected.

INTERPRETATION

Overall, the results appear to support the efficacy of zone 2 calf-lengthening for children with Cerebral Palsy and Idiopathic Toe Walking.

Plantar flexor voluntary activation capacity, strength and function in cerebral palsy

PURPOSE

Distal lower limb motor impairment impacts gait mechanics in individuals with cerebral palsy (CP), however, the contribution of impairments of muscle activation to reduced gross motor function (GMF) is not clear. This study aimed to investigate deficits in plantar flexion voluntary activation capacity in CP compared to typically developed (TD) peers, and evaluate relationships between voluntary activation capacity, strength and GMF.

METHODS

Fifteen ambulant individuals with spastic CP (23 ± 6 years, GMFCS I-III) and 14 TD (22 ± 2 years) people participated. Plantar- and dorsiflexion strength were assessed with a dynamometer. Voluntary activation capacity was assessed using the interpolated twitch technique via single twitch supramaximal tibial nerve stimulation. GMF was assessed using the timed upstairs test, 10 m walk test, muscle power sprint test and six-minute walk test.

RESULTS

Plantar- and dorsiflexion strength were 55.6% and 60.7% lower in CP than TD (p < 0.001). Although voluntary activation capacity was 17.9% lower on average for CP than TD (p = 0.039), 46.7% of individuals with CP achieved a sufficiently high activation to fall within one standard deviation of the TD mean. Plantar flexion voluntary activation capacity did not correlate with strength (R² = 0.092, p = 0.314) or GMF measures in the high functioning CP group (GMFCS I-II).

CONCLUSION

In contrast to previous research, plantar flexion activation capacity did not strongly predict weakness or reduced GMF. We propose that muscle size contributes more to weakness than voluntary activation capacity in high functioning individuals with CP and that relationships between muscle activation and functional capacity are complicated by effects at multiple joints.

Is there a relationship between muscle-tendon properties and a variety of functional tasks in children with spastic cerebral palsy?

BACKGROUND

Cerebral palsy (CP) is the most common motor and movement disability in childhood. The mechano-morphological alterations of the spastic muscle itself as well as the functional limitations in CP are well documented. However, the relationship between muscle tendon properties and functional tests in CP remains unknown.

RESEARCH QUESTION

The aim of this study was to explore the relationship between spastic muscle mechano-morphological properties and functional performance in children with CP.

METHODS

This study included retrospective data from 22 children with spastic cerebral palsy with a mean age of 12.8 years (19 GMFCS I/3 GMFC II, 15 male/7 female, 8 unilateral involved/14 bilateral). Mechano-morphological properties of gastrocnemius (GM) and Achilles tendon (AT) were correlated with a variety of functional measures, maximal isometric strength, the Muscle Power Sprint test (MPST), 6-minute walk test (6MWT) and 3D-gait analysis using the Pearson Coefficient.

RESULTS

Muscle-tendon properties were normalized to remove anthropometric dimensions because of strong associations with anthropometric data. Higher isometric muscle strength was related to longer normalized GM fascicle lengths (r = 0.67, p < 0.01). The distance reached in the 6MWT positively correlated with normalized GM fascicle lengths (r = 0.61, p < 0.01). Higher AT stiffness was associated with faster performance in the MPST (r = 0.77, p < 0.01). Finally, there was an association between ankle power and both longer normalized AT length and shorter muscle belly (r = 0.60 and r = 0.54, p < 0.01).

SIGNIFICANCE

The findings of this study give more insight into the function specific adaptations of a spastic muscle-tendon unit. While walking, assessed through the 6MWT, was related to normalized gastrocnemius fascicle length, sprint performance was associated with an increased AT stiffness. These results provide a better understanding of the relationship between functional tasks and spastic muscle-tendon properties, which offers potential for improved and targeted interventions in CP.

Measuring skeletal muscle morphology and architecture with imaging modalities in children with cerebral palsy: a scoping review

AIM

To investigate the use of ultrasound and magnetic resonance imaging (MRI) methodologies to assess muscle morphology and architecture in children with cerebral palsy (CP).

METHOD

A scoping review was conducted with systematic searches of Medline, Embase, Scopus, Web of Science, PubMed, and PsycInfo for all original articles published up to January 2019 utilizing ultrasound and/or MRI to determine morphological and architectural properties of lower limb skeletal muscle in children with CP.

RESULTS

Eighty papers used ultrasound (n=44), three-dimensional ultrasound (n=16), or MRI (n=20) to measure at least one muscle parameter in children and adolescents with CP. Most research investigated single muscles, predominantly the medial gastrocnemius muscle, included children classified in Gross Motor Function Classification System levels I (n=62) and II (n=65), and assessed fascicle length (n=35) and/or muscle volume (n=35). Only 21 papers reported reliability of imaging techniques. Forty-six papers assessed measures of Impairment (n=39), Activity (n=24), and Participation (n=3).

INTERPRETATION

Current research study design, variation in methodology, and preferences towards investigation of isolated muscles may oversimplify the complexities of CP muscle but provide a foundation for the understanding of the changes in muscle parameters in children with CP.

WHAT THIS PAPER ADDS

Current evidence is biased towards the medial gastrocnemius muscle and more functionally able children with cerebral palsy (CP). Variations in imaging techniques and joint positioning limit comparisons between studies. Clinimetric testing of parameters of CP muscle is not always considered. Assessment of parameter(s) of muscle with measures of participation is sparse.

Automatic generation of personalised skeletal models of the lower limb from three-dimensional bone geometries

The generation of personalised and patient-specific musculoskeletal models is currently a cumbersome and time-consuming task that normally requires several processing hours and trained operators. We believe that this aspect discourages the use of computational models even when appropriate data are available and personalised biomechanical analysis would be beneficial. In this paper we present a computational tool that enables the fully automatic generation of skeletal models of the lower limb from three-dimensional bone geometries, normally obtained by segmentation of medical images. This tool was evaluated against four manually created lower limb models finding remarkable agreement in the computed joint parameters, well within human operator repeatability. The coordinate systems origins were identified with maximum differences between 0.5 mm (hip joint) and 5.9 mm (subtalar joint), while the joint axes presented discrepancies between 1° (knee joint) to 11° (subtalar joint). To prove the robustness of the methodology, the models were built from four datasets including both genders, anatomies ranging from juvenile to elderly and bone geometries reconstructed from high-quality computed tomography as well as lower-quality magnetic resonance imaging scans. The entire workflow, implemented in MATLAB scripting language, executed in seconds and required no operator intervention, creating lower extremity models ready to use for kinematic and kinetic analysis or as baselines for more advanced musculoskeletal modelling approaches, of which we provide some practical examples. We auspicate that this technical advancement, together with upcoming progress in medical image segmentation techniques, will promote the use of personalised models in larger-scale studies than those hitherto undertaken.

Impact of Lower Limb Active Movement Training in Individuals With Spastic Type Cerebral Palsy on Neuromuscular Control Outcomes: A Systematic Review

Background: Cerebral Palsy (CP) is a non-progressive neurological condition that results in motor impairment which increases proximally to distally along the lower extremity (i.e., greatest impairment at the ankle). Consequently, motor impairment and reduced voluntary muscle activation results in reduced neuromuscular control of the lower limb in this population. CP rehabilitation traditionally aims to improve movement proficiency for functional activities, such as walking, by using a range of active movement modalities that require volitional effort; however, the underlying neural mechanisms of improved control and function remain unknown. The primary purpose of this study was to systematically determine the efficacy of lower limb active movement interventions to improve neuromuscular control in individuals with CP.

Methodology: A search for studies involving an active lower limb intervention and neurophysiological outcome measures in individuals with CP was performed in five electronic databases. Studies were assessed for methodological quality using the Downs and Black assessment tool.

Results: Nine of 6,263 articles met the inclusion criteria. Methodological quality of all studies was poor, ranging from 2 to 27 out of a possible score of 32 points on the Downs and Black assessment tool. The study interventions varied extensively in modality and prescription as well as in the outcome measures used.

Conclusions: Whether active movement improves neuromuscular control of the lower limb in CP is unclear due to high variability in intervention protocols and selected outcomes measures. Future active intervention studies must carefully consider the selection of neurophysiological outcome measures.

Automatic Tracking of the Muscle Tendon Junction in Healthy and Impaired Subjects using Deep Learning

Recording muscle tendon junction displacements during movement, allows separate investigation of the muscle and tendon behaviour, respectively. In order to provide a fully-automatic tracking method, we employ a novel deep learning approach to detect the position of the muscle tendon junction in ultrasound images. We utilize the attention mechanism to enable the network to focus on relevant regions and to obtain a better interpretation of the results. Our data set consists of a large cohort of 79 healthy subjects and 28 subjects with movement limitations performing passive full range of motion and maximum contraction movements. Our trained network shows robust detection of the muscle tendon junction on a diverse data set of varying quality with a mean absolute error of 2.55 ± 1 mm. We show that our approach can be applied for various subjects and can be operated in real-time. The complete software package is available for open-source use.

Impact of Altered Gastrocnemius Morphometrics and Fascicle Behavior on Walking Patterns in Children With Spastic Cerebral Palsy

Spastic cerebral palsy (SCP) affects neural control, deteriorates muscle morphometrics, and may progressively impair functional walking ability. Upon passive testing, gastrocnemius medialis (GM) muscle bellies or fascicles are typically shorter, thinner, and less extensible. Relationships between muscle and gait parameters might help to understand gait pathology and pathogenesis of spastic muscles. The current aim was to link resting and dynamic GM morphometrics and contractile fascicle behavior (both excursion and velocity) during walking to determinants of gait. We explored the associations between gait variables and ultrasonography of the GM muscle belly captured during rest and during gait in children with SCP [n = 15, gross motor function classification system (GMFCS) levels I and II, age: 7–16 years] and age-matched healthy peers (n = 17). The SCP children’s plantar flexors were 27% weaker. They walked 12% slower with more knee flexion produced 42% less peak ankle push-off power (all p < 0.05) and 7/15 landed on their forefoot. During the stance phase, fascicles in SCP on average operated on 9% shorter length (normalized to rest length) and displayed less and slower fascicle shortening (37 and 30.6%, respectively) during push-off (all p ≤ 0.024). Correlation analyses in SCP patients revealed that (1) longer-resting fascicles and thicker muscle bellies are positively correlated with walking speed and negatively to knee flexion (r = 0.60–0.69, p < 0.0127) but not to better ankle kinematics; (2) reduced muscle strength was associated with the extent of eccentric fascicle excursion (r = −0.57, p = 0.015); and (3) a shorter operating length of the fascicles was correlated with push-off power (r = −0.58, p = 0.013). Only in controls, a correlation (r = 0.61, p = 0.0054) between slower fascicle shortening velocity and push-off power was found. Our results indicate that a thicker gastrocnemius muscle belly and longer gastrocnemius muscle fascicles may be reasonable morphometric properties that should be targeted in interventions for individuals with SCP, since GM muscle atrophy may be related to decreases in walking speed and undesired knee flexion during gait. Furthermore, children with SCP and weaker gastrocnemius muscle may be more susceptible to chronic eccentric muscle overloading. The relationship between shorter operating length of the fascicles and push-off power may further support the idea of a compensation mechanism for the longer sarcomeres found in children with SCP. Nevertheless, more studies are needed to support our explorative findings.

Effective Mechanical Advantage About the Ankle Joint and the Effect of Achilles Tendon Curvature During Toe-Walking

Aim: To study the causes of locomotor dysfunction, estimate muscle forces, or understand the influence of altered sarcomere and muscle properties and behaviours on whole body function, it is necessary to examine the leverage with which contractile forces operate. At the ankle joint, current methods to quantify this leverage for the plantarflexors do not account for curvature of the Achilles tendon, and so may not be appropriate when studying equinus gait. Thus, novel methodologies need to be developed and implemented to quantify the Achilles tendon moment arm length during locomotion. Methods: Plantarflexor internal moment arm length and effective mechanical advantage of 11 typically developed young adults were calculated throughout stance, while heel-toe walking and voluntarily toe-walking on an instrumented treadmill. Achilles tendon moment arm was defined in two-ways: (1) assuming a straight tendon, defined between the gastrocnemius medialis myotendinous junction and Achilles tendon insertion point, and (2) accounting for tendon curvature, by tracking the initial path of the Achilles tendon from the calcaneal insertion. Results: When accounting for tendon curvature, Achilles tendon moment arm length and plantarflexor effective mechanical advantage did not differ between walking conditions (p > 0.05). In contrast, when assuming a straight tendon, Achilles tendon moment arm length (p = 0.043) and plantarflexor effective mechanical advantage (p = 0.007) were significantly greater when voluntary toe-walking than heel-toe walking in late stance. Discussion: Assuming a straight Achilles tendon led to a greater Achilles tendon moment arm length and plantarflexor effective mechanical advantage during late stance, compared to accounting for tendon curvature. Consequently, plantarflexor muscle force would appear smaller when assuming a straight tendon. This could lead to erroneous interpretations of muscular function and fascicle force-length-velocity behaviour in vivo, and potentially inappropriate and ineffective clinical interventions for equinus gait.

Automated Generation of Three-Dimensional Complex Muscle Geometries for Use in Personalised Musculoskeletal Models

The geometrical representation of muscles in computational models of the musculoskeletal system typically consists of a series of line segments. These muscle anatomies are based on measurements from a limited number of cadaveric studies that recently have been used as atlases for creating subject-specific models from medical images, so potentially restricting the options for personalisation and assessment of muscle geometrical models. To overcome this methodological limitation, we propose a novel, completely automated technique that, from a surface geometry of a skeletal muscle and its attachment areas, can generate an arbitrary number of lines of action (fibres) composed by a user-defined number of straight-line segments. These fibres can be included in standard musculoskeletal models and used in biomechanical simulations. This methodology was applied to the surfaces of four muscles surrounding the hip joint (iliacus, psoas, gluteus maximus and gluteus medius), segmented on magnetic resonance imaging scans from a cadaveric dataset, for which highly discretised muscle representations were created and used to simulate functional tasks. The fibres’ moment arms were validated against measurements and models of the same muscles from the literature with promising outcomes. The proposed approach is expected to improve the anatomical representation of skeletal muscles in personalised biomechanical models and finite element applications.

Ultrasound imaging to assess skeletal muscle architecture during movements: a systematic review of methods, reliability, and challenges

B-mode ultrasound is often used to quantify muscle architecture during movements. Our objectives were to 1) systematically review the reliability of fascicle length (FL) and pennation angles (PA) measured using ultrasound during movements involving voluntary contractions; 2) systematically review the methods used in studies reporting reliability, discuss associated challenges, and provide recommendations to improve the reliability and validity of dynamic ultrasound measurements; and 3) provide an overview of computational approaches for quantifying fascicle architecture, their validity, agreement with manual quantification of fascicle architecture, and advantages and drawbacks. Three databases were searched until June 2019. Studies among healthy human individuals aged 17-85 yr that investigated the reliability of FL or PA in lower-extremity muscles during isoinertial movements and that were written in English were included. Thirty studies (n = 340 participants) were included for reliability analyses. Between-session reliability as measured by coefficient of multiple correlations (CMC), and coefficient of variation (CV) was FL CMC: 0.89-0.96; CV: 8.3% and PA CMC: 0.87-0.90; CV: 4.5-9.6%. Within-session reliability was FL CMC: 0.82-0.99; CV: 0.0-6.7% and PA CMC: 0.91; CV: 0.0-15.0%. Manual analysis reliability was FL CMC: 0.89-0.96; CV: 0.0-15.9%; PA CMC: 0.84-0.90; and CV: 2.0-9.8%. Computational analysis FL CMC was 0.82-0.99, and PA CV was 14.0-15.0%. Eighteen computational approaches were identified, and these generally showed high agreement with manual analysis and high validity compared with phantoms or synthetic images. B-mode ultrasound is a reliable method to quantify fascicle architecture during movement. Additionally, computational approaches can provide a reliable and valid estimation of fascicle architecture.

Flip-flops do not alter the neuromuscular function of the gastrocnemius muscle and tendon during walking in children

INTRODUCTION/AIM

Flip-flops are a popular choice of footwear for children. However, their inherent design provides minimal support to the foot and ankle and has been suggested to increase the work performed by muscle and tendon structures, potentially predisposing them to injury. Therefore, the aim of this study was to compare the length change behaviour of the medial gastrocnemius (MG) muscle fascicles and muscle tendon unit (MTU) and their mechanical function at the ankle and subtalar joints in children during walking with and without flip-flop.

METHODS

Eight healthy children walked barefoot and with flip-flops whilst 3D gait analysis and simultaneous B-mode ultrasound images of the MG fascicles during level walking were collected. Joint kinematics, kinetics and MTU lengths were analysed using musculoskeletal modelling and fascicle lengths using a semi-automated tracking algorithm.

RESULTS

The muscles and tendons across the ankle absorbed greater amounts of power during barefoot walking compared to flip-flop walking. The muscle activations of the lateral gastrocnemius, soleus and tibialis anterior remained invariant across the conditions as did the activation, and fascicle length change behaviour of the medial gastrocnemius. In the barefoot condition, there was a trend of greater MTU lengthening, to potentially absorb greater amounts of power, although no differences in shortening was observed during late stance.

CONCLUSION

Walking with flip-flops does not increase the mechanical work performed by the MG muscle at the ankle and subtalar joints, suggesting that flip-flops do not increase the stresses and strains of the Achilles tendon and hence its predisposition to strain induced injury. Instead, our results suggest that flip-flops, act as a compliant surface and absorb energy during contact and hence the strain experienced by the Achilles tendon.

Maturation of feedforward toe walking motor program is impaired in children with cerebral palsy

Voluntary toe walking in adults is characterized by feedforward control of ankle muscles in order to ensure optimal stability of the ankle joint at ground impact. Toe walking is frequently observed in children with cerebral palsy, but the mechanisms involved have not been clarified. Here, we investigated maturation of voluntary toe walking in typically-developing children and typically-developed adults and compared it to involuntary toe walking in children with cerebral palsy. Twenty-eight children with cerebral palsy (age 3-14 years), 24 typically-developing children (age 2-14 years) and 15 adults (mean age 30.7 years) participated in the study. EMG activity was measured from the tibialis anterior and soleus muscles together with knee and ankle joint position during treadmill walking. In typically-developed adults, low step-to-step variability of the drop of the heel after ground impact was correlated with low tibialis anterior and high soleus EMG with no significant coupling between the antagonist muscle EMGs. Typically-developing children showed a significant age-related decline in EMG amplitude reaching an adult level at 10-12 years of age. The youngest typically-developing children showed a broad peak EMG-EMG synchronization (>100 ms) associated with large 5-15 Hz coherence between antagonist muscle activities. EMG coherence declined with age and at the age of 10-12 years no correlation was observed similar to adults. This reduction in coherence was closely related to improved step-to-step stability of the ankle joint position. Children with cerebral palsy generally showed lower EMG levels than typically-developing children and larger step-to-step variability in ankle joint position. In contrast to typically-developing children, children with cerebral palsy showed no age-related decline in tibialis anterior EMG amplitude. Motor unit synchronization and 5-15 Hz coherence between antagonist EMGs was observed more frequently in children with cerebral palsy when compared to typically-developing children and in contrast to typically-developing participants there was no age-related decline. We conclude that typically-developing children develop mature feedforward control of ankle muscle activity as they age, such that at age 10-12 years there is little agonist-antagonist muscle co-contraction around the time of foot-ground contact during toe walking. Children with cerebral palsy, in contrast, continue to co-contract agonist and antagonist ankle muscles when toe walking. We speculate that children with cerebral palsy maintain a co-contraction activation pattern when toe walking due to weak muscles and insufficient motor and sensory signalling necessary for optimization of feedforward motor programs. These findings are important for understanding of the pathophysiology and treatment of toe walking.

Gait deficits and dynamic stability in children and adolescents with cerebral palsy: A systematic review and meta-analysis

BACKGROUND

Studies have demonstrated that ambulatory children and adolescents with cerebral palsy demonstrate atypical gait patterns. Out of numerous gait variables, identification of the most deteriorated gait parameters is important for targeted and effective gait rehabilitation. Therefore, this study aimed to identify the gait parameters with the most discriminating nature to distinguish cerebral palsy gait from normal gait.

METHODS

Multiple databases were searched to include studies on ambulatory children and adolescents with cerebral palsy that included gait (spatio-temporal, kinematic, and kinetic) and dynamic stability variables.

FINDINGS

Of 68 studies that met the inclusion criteria, 35 studies were included in the meta analysis. Effect size was used to assess the discriminative strength of each variable. A large effect (≥ 0.8) of cerebral palsy on double limb support time (Standardized Mean Difference = 0.98), step length (Standardized Mean Difference = 1.65), step width (Standardized Mean Difference = 1.21), stride length (Standardized Mean Difference = 1.75), and velocity (Standardized Mean Difference = 1.42) was observed at preferred-walking speed. At fast-walking speed, some gait variables (i.e. velocity and stride length) exhibited larger effect size compared to preferred-walking speed. For some kinematic variables (e.g. range of motion of pelvis), the effect size varied across the body planes.

INTERPRETATION

Our systematic review detects the most discriminative features of cerebral palsy gait. Non-uniform effects on joint kinematics across the anatomical planes support the importance of 3D gait analysis. Differential effects at fast versus preferred speeds emphasize the importance of measuring gait at a range of speeds.

Semi-automatic methods for tracking the medial gastrocnemius muscle-tendon junction using ultrasound: a validation study

NEW FINDINGS

What is the central question of this study? Is the proposed semi-automatic algorithm suitable for tracking the medial gastrocnemius muscle-tendon junction in ultrasound images collected during passive and active conditions? What is the main finding and its importance? The validation of a method allowing efficient tracking of the muscle-tendon junction in both passive and active conditions, in healthy as well as in pathological conditions. This method was tested in common acquisition conditions and the developed software made freely available.

ABSTRACT

Clinically relevant information can be extracted from ultrasound (US) images by tracking the displacement of the junction between muscle and tendon. This paper validated automatic methods for tracking the location of muscle-tendon junction (MTJ) between the medial gastrocnemius and the Achilles tendon during passive slow and fast stretches, and active ankle rotations while walking on a treadmill. First, an automatic algorithm based on an optical flow approach was applied on collected US images. Second, results of the automatic algorithm were evaluated and corrected using a quality measure that indicated which critical images need to be manually corrected. US images from 12 typically developed (TD) children, 12 children with spastic cerebral palsy (SCP) and eight healthy adults were analysed. Automatic and semi-automatic tracking methods were compared to manual tracking using root mean square errors (RMSE). For the automatic tracking, RMSE was less than 3.1 mm for the slow stretch and 5.2 mm for the fast stretch, the worst case being for SCP. The tracking results in the fast stretch condition were improved (especially in SCP) by using the semi-automatic approach, with an RMSE reduction of about 30%. During walking, the semi-automatic method also reduced errors, with a final RMSE of 3.6 mm. In all cases, data processing was considerably shorter using the semi-automatic method (2 min) compared to manual tracking (20 min). A quick manual correction considerably improves tracking of the MTJ during gait and allows to achieve results suitable for further analyses. The proposed algorithm is freely available.

Ultrasound as a Tool to Study Muscle-Tendon Functions during Locomotion: A Systematic Review of Applications

Movement science investigating muscle and tendon functions during locomotion utilizes commercial ultrasound imagers built for medical applications. These limit biomechanics research due to their form factor, range of view, and spatio-temporal resolution. This review systematically investigates the technical aspects of applying ultrasound as a research tool to investigate human and animal locomotion. It provides an overview on the ultrasound systems used and of their operating parameters. We present measured fascicle velocities and discuss the results with respect to operating frame rates during recording. Furthermore, we derive why muscle and tendon functions should be recorded with a frame rate of at least 150 Hz and a range of view of 250 mm. Moreover, we analyze why and how the development of better ultrasound observation devices at the hierarchical level of muscles and tendons can support biomechanics research. Additionally, we present recent technological advances and their possible application. We provide a list of recommendations for the development of a more advanced ultrasound sensor system class targeting biomechanical applications. Looking to the future, mobile, ultrafast ultrasound hardware technologies create immense opportunities to expand the existing knowledge of human and animal movement.

The effect of combined functional anaerobic and strength training on treadmill gait kinematics and kinetics in ambulatory young adults with cerebral palsy

BACKGROUND

Leg muscle weakness is a major impairment for individuals with cerebral palsy (CP) and is related to reduced functional capacity. Evidence is limited regarding the translation of strength improvements following conventional resistance training to improved gait outcomes.

RESEARCH QUESTION

Does a combined functional anaerobic and lower limb strength training intervention improve gait kinematics and kinetics in individuals with CP aged 15-30 years? 17 young adults (21 ± 4 years, 9 males, GMFCS I = 11, II = 6) were randomized to 12 weeks, 3 sessions per week, of high intensity functional anaerobic and progressive resistance training of the lower limbs (n = 8), or a waitlist control group (n = 9). Pre- and post-training outcomes included maximum ankle dorsiflexion angle at foot contact and during stance, gait profile score, ankle and hip power generation during late stance, and the ratio of ankle to hip power generation.

RESULTS

There were no between-group differences after the intervention for any kinematic or kinetic gait outcome variable. Within-group analysis revealed an increase in peak ankle power during late stance (0.31 ± 0.28 W·kg^-1, p = 0.043) and ankle to hip power ratio (0.43 ± 0.37, p = 0.034) following training in the intervention group.

SIGNIFICANCE

We have previously reported increased overground walking capacity, agility and sprint power, in the training group compared to the control group at 12-weeks. These changes in overground measures of functional capacity occurred in the absence of changes in treadmill gait kinematics and kinetics reported here.

ANZCTR

12614001217695.

Functional Task Training Combined With Electrical Stimulation Improves Motor Capacity in Children With Unilateral Cerebral Palsy: A Single-Subject Design

PURPOSE

Reduced propulsive capability can impact negatively on mobility activities of many children with spastic unilateral cerebral palsy (SUCP). This study investigated the effect of a task-oriented training program combined with functional electrical stimulation (FES) on the motor capacity of children with SUCP.

METHODS

Single-case A-B design with follow-up. Gross motor function and biomechanical walking data of 4 children with SUCP were measured repeatedly across the baseline, intervention, and follow-up phases. Intervention was a task-oriented training program combined with FES applied on the gastrocnemius. Outcome variables included gait speed, impulsive torque, and ankle/hip power generation ratio. The 2-SD band and celeration line methods compared outcomes among the baseline, intervention, and follow-up periods.

RESULTS

One child improved walking speed. All children improved impulsive torque and ankle/hip power ratio of the affected leg. All children improved gross motor function.

CONCLUSION

The intervention improved children's propulsive capability and positively influenced their mobility.

Contribution of corticospinal drive to ankle plantar flexor muscle activation during gait in adults with cerebral palsy

Impaired plantar flexor muscle activation during push-off in late stance contributes importantly to reduced gait ability in adults with cerebral palsy (CP). Here we used low-intensity transcranial magnetic stimulation (TMS) to suppress soleus EMG activity during push-off as an estimate of corticospinal drive in CP adults and neurologically intact (NI) adults. Ten CP adults (age 34 years, SD 14.6, GMFCS I-II) and ten NI adults (age 33 years, SD 9.8) walked on a treadmill at their preferred walking speed. TMS of the leg motor cortex was elicited just prior to push-off during gait at intensities below threshold for motor-evoked potentials. Soleus EMG from steps with and without TMS were averaged and compared. Control experiments were performed while standing and in NI adults during gait at slow speed. TMS induced a suppression at a latency of about 40 ms. This suppression was similar in the two populations when differences in control EMG and gait speed were taken into account (CP 18%, NI 16%). The threshold of the suppression was higher in CP adults. The findings suggest that corticospinal drive to ankle plantar flexors at push-off is comparable in CP and NI adults. The higher threshold of the suppression in CP adults may reflect downregulation of cortical inhibition to facilitate corticospinal drive. Interventions aiming to facilitate excitability in cortical networks may contribute to maintain or even improve efficient gait in CP adults.

Characterization of torque generating properties of ankle plantar flexor muscles in ambulant adults with cerebral palsy

PURPOSE

Weakness of plantar flexor muscles is related to reduced push-off and forward propulsion during gait in persons with cerebral palsy (CP). It has not been clarified to what an extent altered muscle contractile properties contribute to this muscle weakness. Here, we investigated the torque generating capacity and muscle fascicle length in the triceps surae muscle throughout ankle range of motion (ROM) in adults with CP using maximal single muscle twitches elicited by electrical nerve stimulation and ultrasonography.

METHODS

Fourteen adults with CP (age 36, SD 10.6, GMFCS I-III) and 17 neurological intact (NI) adults (age 36, SD 4.5) participated. Plantar flexor torque during supramaximal stimulation of the tibial nerve was recorded in a dynamometer at 8 ankle angles throughout ROM. Medial gastrocnemius (MG) fascicle length was tracked using ultrasonography.

RESULTS

Adults with CP showed reduced plantar flexor torque and fascicle shortening during supramaximal stimulation throughout ROM. The largest torque generation was observed at the ankle joint position where the largest shortening of MG fascicles was observed in both groups. This was at a more plantarflexed position in the CP group.

CONCLUSION

Reduced torque and fascicle shortening during supramaximal stimulation of the tibial nerve indicate impaired contractile properties of plantar flexor muscles in adults with CP. Maximal torque was observed at a more plantarflexed position in adults with CP indicating an altered torque-fascicle length/ankle angle relation. The findings suggest that gait rehabilitation in adults with CP may require special focus on improvement of muscle contractility.

Combining muscle morphology and neuromotor symptoms to explain abnormal gait at the ankle joint level in cerebral palsy

BACKGROUND

Individuals with spastic cerebral palsy (CP) have neuromotor symptoms contributing towards their gait patterns. However, the role of altered muscle morphology alongside these symptoms is yet to be fully investigated.

RESEARCH QUESTION

To what extent can medial gastrocnemius and tibialis anterior volume and echo-intensity, plantar/dorsiflexion strength and selective motor control, plantarflexion spasticity and passive ankle dorsiflexion explain abnormal ankle gait.

METHOD

In thirty children and adolescents with spastic CP (8.6 ± 3.4 y/mo) and ten typically developing peers (9.9 ± 2.4 y/mo), normalised muscle volume and echo-intensity were estimated. Both cohorts also underwent three-dimensional gait analysis, whilst for participants with spastic CP, plantar/dorsi-flexion strength and selective motor control, plantarflexion spasticity and maximum ankle dorsiflexion were also measured. The combined contribution of these parameters towards five clinically meaningful features of gait were evaluated, using backwards multiple regression analyses.

RESULTS

With respect to the typically developing cohort, the participants with spastic CP had deficits in normalised medial gastrocnemius and tibialis anterior volume of 40% and 33%, and increased echo-intensity values of 19% and 16%, respectively. The backwards multiple regression analyses revealed that the combination of reduced ankle dorsiflexion, muscle volume, plantarflexion strength and dorsiflexion selective motor control could account for 12-62% of the variance in the chosen features of gait.

SIGNIFICANCE

The combination of altered muscle morphology and neuromotor symptoms partly explained abnormal gait at the ankle in children with spastic CP. Both should be considered as important measures for informed treatment decision-making, but further work is required to better unravel the complex pathophysiology.

Validity and reliability of a freehand 3D ultrasound system for the determination of triceps surae muscle volume in children with cerebral palsy

This study assessed the validity, intra-rater and inter-rater reliability of segmentation of in vivo medial gastrocnemius (MG), lateral gastrocnemius (LG) and soleus (SOL) muscle volume measurement using a single sweep freehand 3D ultrasound (3DUS) in children with cerebral palsy (CP). The MG, LG and SOL of both limbs of 18 children with CP (age 8 years 4 months ± 1 year 10 months, 11 males, unilateral CP = 9, bilateral CP = 9, Gross Motor Functional Classification System I = 11, II = 7) were scanned using freehand 3DUS and magnetic resonance imaging (MRI). All freehand 3DUS and MRI images were segmented and volumes rendered by two raters. Validity was assessed using limits of agreement method. Intra-rater and inter-rater reliability was assessed using intra-class correlation (ICC), coefficient of variance (CV) and minimal detectable change (MDC). Freehand 3DUS overestimated muscle volume of the MG and LG by < 0.3 mL (1%) and underestimated SOL by < 1.3 mL (1.5%) compared with MRI. ICCs for intra-rater reliability of the segmentation process for the freehand 3DUS system and MRI for muscle volume were > 0.98 and 0.99, respectively, for all muscles. ICCs for inter-rater reliability of the segmentation process for freehand 3DUS and MRI volumes were > 0.96 and 0.98, respectively, for all muscles. MDCs for single rater freehand 3DUS and MRI were < 4.0 mL (14%) and 3.2 mL (11%), respectively, in all muscles. Freehand 3DUS is a valid and reliable method for the measurement of lower leg muscle volume that can be measured with a single sweep in children with CP in vivo. It can be used as an alternative to MRI for the detection of clinically relevant changes in calf muscle volume as the result of growth and interventions.

Usefulness of a Qualitative Ultrasound Evaluation of the Gastrocnemius-Soleus Complex with the Heckmatt Scale for Clinical Practice in Cerebral Palsy

Ultrasound is increasingly used for the evaluation of spastic muscles in cerebral palsy. Increased echo intensity is considered indicative of a muscle fibrous involution. The aim of this study was to highlight any correlation between increased echo intensity of the gastrocnemius-soleus complex and clinical tests for stiffness evaluation, age and functional level measured with the Gross Motor Function Classification System. We used the qualitative echo intensity grading system of the Heckmatt scale (HS) and tested its inter-rater reliability. The study group comprised 60 patients with cerebral palsy. We found a weak significant correlation between HS scores and clinical stiffness measures and between HS and age for all muscles studied, and between the HS and Gross Motor Function Classification System only for the soleus muscle. The study indicated moderate inter-rater reliability, with κ values between 0.60 and 0.73, for almost all muscles studied. Ultrasound provides a useful complementary survey of stiffness tests in cerebral palsy.

Medial Gastrocnemius Muscle-Tendon Junction and Fascicle Lengthening across the Range of Motion Analyzed in 2-D and 3-D Ultrasound Images

Ultrasound imaging modalities offer a clinically viable method to visualize musculoskeletal structures. However, proper data comparison between investigations is compromised because of a lack of measurement error documentation and method standardization. This investigation analyzes the reliability and validity of extracting medial gastrocnemius belly and fascicle lengths and pennation angles in different ankle joint positions, across the full range of motion, in a cohort of 11 children with spastic cerebral palsy and 11 typically developed children. Each of these parameters was extracted from two consecutive acquisitions, using both 2-D and 3-D ultrasound images. The findings suggest that the muscle tendon junction extraction in 2-D images can be a suitable parameter for analyzing medial gastrocnemius muscle length in typically developed children and children with spastic cerebral palsy, although averaging over multiple measurements is recommended to reduce variability. More caution should be taken when performing analyses based on fascicle length.

Reliability of joint kinematic calculations based on direct kinematic and inverse kinematic models in obese children

BACKGROUND

In recent years, the reliability of inverse (IK) and direct kinematic (DK) models in gait analysis have been assessed intensively, but mainly for lean populations. However, obesity is a growing issue. So far, the sparse results available for the reliability of clinical gait analysis in obese populations are limited to direct kinematic models. Reliability error-margins for inverse kinematic models in obese populations have not been reported yet.

RESEARCH QUESTIONS

Is there a difference in the reliability of IK models compared with a DK model in obese children? Are there any differences in the joint kinematic output between IK and DK models?

METHODS

A test-retest study was conducted using three-dimensional gait analysis data from two obese female and eight obese male participants from an earlier study. Data were analyzed using a DK model and two OpenSim-based IK models. Test-retest reliability was compared by calculating the Standard Error of Measurement (SEM) along with similar absolute reliability measures. A Friedman Test was used to assess whether there were any significant differences in the reliability between the models. Kinematic output of the models was compared by using Statistical Parametric Mapping (SPM).

RESULTS

No significant differences were found in the reliability between the DK and IK models. The SPM analysis indicated several significant differences between both IK models and the DK approach. Most of these differences were continuous offsets.

SIGNIFICANCE

Reliability values showed clinically acceptable error-margins and were comparable between all models. Therefore, our results support the careful use of IK models in overweight or obese populations, e.g. for musculoskeletal modelling studies. The inconsistent kinematic output can mainly be explained by different model conventions and anatomical segment coordinate frame definitions.

The influence of maximum isometric muscle force scaling on estimated muscle forces from musculoskeletal models of children with cerebral palsy

BACKGROUND

Musculoskeletal models do not include patient-specific muscle forces but rely on a scaled generic model, with muscle forces left unscaled in most cases. However, to use musculoskeletal simulations to inform clinical decision-making in children with cerebral palsy (CP), inclusion of subject-specific muscle forces is of utmost importance in order to represent each child's compensation mechanisms introduced through muscle weakness.

RESEARCH AIM

The aims of this study were to (i) evaluate if maximum isometric muscle forces (MIMF) in musculoskeletal models of children with CP can be scaled based on strength measurements obtained with a hand-held-dynamometer (HHD), (ii) evaluate the impact of the HHD based scaling approach and previously published MIMF scaling methods on computed muscle forces during gait, and (iii) compare maximum muscle forces during gait between CP and typically developing (TD) children.

METHODS

Strength and motion capture data of six CP and motion capture data of six TD children were collected. The HHD measurements to obtain hip, knee and ankle muscle strength were simulated in OpenSim and used to modify MIMF of the 2392-OpenSim model. These muscle forces were compared to the MIMF scaled on the child's body mass and a scaling approach, which included the body mass and muscle-tendon lengths. OpenSim was used to calculate peak muscle forces during gait.

RESULTS

Ankle muscle strength was insufficient to reproduce joint moments during walking when MIMF were scaled based on HHD. During gait, peak hip and knee extensor muscle forces were higher and peak ankle dorsi-flexor forces were lower in CP compared to TD participants.

SIGNIFICANCE

HHD measurements can be used to scale MIMF for the hip and knee muscle groups but underestimate the force capacity of the ankle muscle groups during walking. Muscle-tendon-length and mass based scaling methods affected muscle activations but had little influence on peak muscle forces during gait.

Medial gastrocnemius structure and gait kinetics in spastic cerebral palsy and typically developing children: A cross-sectional study

To compare medial gastrocnemius muscle-tendon structure, gait propulsive forces, and ankle joint gait kinetics between typically developing children and those with spastic cerebral palsy, and to describe significant associations between structure and function in children with spastic cerebral palsy.A sample of typically developing children (n = 9 /16 limbs) and a sample of children with spastic cerebral palsy (n = 29 /43 limbs) were recruited. Ultrasound and 3-dimensional motion capture were used to assess muscle-tendon structure, and propulsive forces and ankle joint kinetics during gait, respectively.Children with spastic cerebral palsy had shorter fascicles and muscles, and longer Achilles tendons than typically developing children. Furthermore, total negative power and peak negative power at the ankle were greater, while total positive power, peak positive power, net power, total vertical ground reaction force, and peak vertical and anterior ground reaction forces were smaller compared to typically developing children. Correlation analyses revealed that smaller resting ankle joint angles and greater maximum dorsiflexion in children with spastic cerebral palsy accounted for a significant decrease in peak negative power. Furthermore, short fascicles, small fascicle to belly ratios, and large tendon to fascicle ratios accounted for a decrease in propulsive force generation.Alterations observed in the medial gastrocnemius muscle-tendon structure of children with spastic cerebral palsy may impair propulsive mechanisms during gait. Therefore, conventional treatments should be revised on the basis of muscle-tendon adaptations.