Feedforward neural control of toe walking in humans

Relation between stretch and activation of the medial gastrocnemius muscle during gait in children with cerebral palsy compared to typically developing children

Stretch hyperreflexia is often a target for treatment to improve gait in children with spastic cerebral palsy (CP). However, the presence of stretch hyperreflexia during gait remains debated. Therefore, we assessed the relation between gastrocnemius medialis muscle-tendon stretch and muscle activation during gait in children with CP compared to typically developing (TD) children. 3D gait analysis including electromyography (EMG) and dynamic ultrasound was carried out to assess, respectively gastrocnemius medialis activation and fascicle, belly, and tendon stretch during treadmill walking. Musculotendon-unit stretch was also estimated using OpenSim. Ratios of EMG/peak lengthening velocities and accelerations were compared between CP and TD. Velocity and acceleration peaks prior to EMG peaks were qualitatively assessed. EMG/velocity and EMG/acceleration ratios were up to 500% higher for CP (n = 14) than TD (n = 15) for most structures. Increased late swing muscle activation in CP was often preceded by fascicle and musculotendon-unit peak lengthening velocity, and early stance muscle activation by peaks in multiple structures. Increased muscle activation in CP is associated with muscle-tendon stretch during gait. Concluding, late swing muscle activation in CP appears velocity-dependent, whereas early stance activation can be velocity- and acceleration-dependent. These insights into stretch reflex mechanisms during gait can assist development of targeted interventions.

Efficacy of tissue-bone homeostasis manipulation on the gait and knee function for the patients with knee osteoarthritis: a randomized controlled trial

BACKGROUND

Knee osteoarthritis (KOA) was characterized by pain and limited joint function, which seriously affected the quality of life of patients. The vast majority of KOA was closely related to degeneration of the patellofemoral joint and abnormal patellar movement trajectory. Tissue-bone homeostasis manipulation (TBHM) could correct abnormal patellar movement trajectory on the basis of loosening soft tissue. However, there was little strong evidence to verify its efficacy on the patients with KOA. The study objective was to explore the efficacy of the TBHM on gait and knee function in the patients with KOA.

METHODS

Sixty KOA patients were randomly assigned to either the joint mobilization (n = 30) or TBHM (n = 30) group. The joint mobilization group received joint mobilization, while the TBHM group received TBHM. For two groups, the patients participated in 30 min rehabilitation sessions thrice per week for 12 weeks. The primary outcome was biomechanical gait outcomes during walking, including step length, step velocity, double support, knee range of motion (ROM), and knee adduction moment (KAM). The secondary outcomes were the Western Ontario and McMaster Index (WOMAC) and 36-Item short- form health survey (SF-36), which reflected improvements in knee function and quality of life, respectively. At baseline and 12 weeks, evaluations were conducted and compared between groups.

RESULTS

After a 12-week intervention, significant group differences were observed in KAM (p = 0.018), WOMAC-Pain (p = 0.043) and WOMAC-Stiffness (p = 0.026). A noteworthy finding was the presence of a significant interaction effect between group and time specifically observed in step velocity during gait (p = 0.046), WOMAC-Function (p = 0.013) and SF-36 (p = 0.027). Further analysis revealed a significant difference in step velocity (p = 0.034), WOMAC-Function (p = 0.025) and SF-36 (p = 0.042) during post-assessment between the two groups. Moreover, a significant time effect was observed across all outcomes of the two groups (p < 0.05).

CONCLUSION

The TBHM intervention has better improved the gait, knee function, and quality of life in the patients with KOA.

TRIAL REGISTRATION

ITMCTR, ITMCTR2200005507. Registered 06/01/2022, http://itmctr.ccebtcm.org.cn/zh-CN/Home/ProjectView?pid=09cdadad-0aef-41ee-81bd-a8dceb63f7f5 .

A Pilot Study of Idiopathic Toe Walking: Measures and Outcomes

This pilot study sought to determine the feasibility of quantifying sensory processing, postural control, motor skill development and participation in daily life in children with idiopathic toe walking (ITW) compared to children without ITW. A nonrandomized, prospective case-control design was employed. Twenty participants were recruited. Computerized weight bearing and postural control data was successfully collected. Differences were found in forefoot/rearfoot weight bearing, balance, sensory-motor abilities and parent reported participation challenges. Sensory processing results were inconclusive. Findings can inform standardized assessment and treatment of ITW.

Predictive simulations identify potential neuromuscular contributors to idiopathic toe walking

BACKGROUND

Most cases of toe walking in children are idiopathic. We used pathology-specific neuromusculoskeletal predictive simulations to identify potential underlying neural and muscular mechanisms contributing to idiopathic toe walking.

METHODS

A musculotendon contracture was added to the ankle plantarflexors of a generic musculoskeletal model to represent a pathology-specific contracture model, matching the reduced ankle dorsiflexion range-of-motion in a cohort of children with idiopathic toe walking. This model was employed in a forward dynamic simulation controlled by reflexes and supraspinal drive, governed by a multi-objective cost function to predict gait patterns with the contracture model. We validated the predicted gait using experimental gait data from children with idiopathic toe walking with ankle contracture, by calculating the root mean square errors averaged over all biomechanical variables.

FINDINGS

A predictive simulation with the pathology-specific model with contracture approached experimental ITW data (root mean square error = 1.37SD). Gastrocnemius activation was doubled from typical gait simulations, but lacked a peak in early stance as present in electromyography. This synthesised idiopathic toe walking was more costly for all cost function criteria than typical gait simulation. Also, it employed a different neural control strategy, with increased length- and velocity-based reflex gains to the plantarflexors in early stance and swing than typical gait simulations.

INTERPRETATION

The simulations provide insights into how a musculotendon contracture combined with altered neural control could contribute to idiopathic toe walking. Insights into these neuromuscular mechanisms could guide future computational and experimental studies to gain improved insight into the cause of idiopathic toe walking.

In Vivo Strain Patterns in the Achilles Tendon During Dynamic Activities: A Comprehensive Survey of the Literature

Achilles' tendon (AT) injuries such as ruptures and tendinopathies have experienced a dramatic rise in the mid- to older-aged population. Given that the AT plays a key role at all stages of locomotion, unsuccessful rehabilitation after injury often leads to long-term, deleterious health consequences. Understanding healthy in vivo strains as well as the complex muscle-tendon unit interactions will improve access to the underlying aetiology of injuries and how their functionality can be effectively restored post-injury. The goals of this survey of the literature with a systematic search were to provide a benchmark of healthy AT strains measured in vivo during functional activities and identify the sources of variability observed in the results. Two databases were searched, and all articles that provided measured in vivo peak strains or the change in strain with respect to time were included. In total, 107 articles that reported subjects over the age of 18 years with no prior AT injury and measured while performing functional activities such as voluntary contractions, walking, running, jumping, or jump landing were included in this review. In general, unclear anatomical definitions of the sub-tendon and aponeurosis structures have led to considerable confusion in the literature. MRI, ultrasound, and motion capture were the predominant approaches, sometimes coupled with modelling. The measured peak strains increased from 4% to over 10% from contractions, to walking, running, and jumping, in that order. Importantly, measured AT strains were heavily dependent on measurement location, measurement method, measurement protocol, individual AT geometry, and mechanical properties, as well as instantaneous kinematics and kinetics of the studied activity. Through a comprehensive review of approaches and results, this survey of the literature therefore converges to a united terminology of the structures and their common underlying characteristics and presents the state-of-knowledge on their functional strain patterns.

Contribution of sensory feedback to Soleus muscle activity during voluntary contraction in humans

Sensory feedback contributes to plantar flexor muscle activity during walking, but it is unknown whether this is also the case during non-locomotor movements. Here, we explored the effect of reduction of sensory feedback to ankle plantar flexors during voluntary isometric contractions. 13 adult volunteers were seated with the right leg attached to a foot plate which could be moved in dorsi- or plantarflexion direction by a computer-controlled motor. During static plantar flexion while the plantar flexors were slowly stretched, a sudden plantar flexion caused a decline in Soleus EMG at stretch reflex latency. This decline in EMG remained when transmission from dorsiflexors was blocked. It disappeared following block of transmission from plantar flexors. Imposed plantarflexion failed to produce a similar decline in EMG during static or ramp-and-hold plantar flexion in the absence of slow stretch. Instead, a decline in EMG was observed 15-20 ms later, which disappeared following block of transmission from dorsiflexors. Imposed plantarflexion in the stance phase during walking caused a decline in SOL EMG which in contrast remained following block of transmission from dorsiflexors. These findings imply that the contribution of spinal interneurons to the neural drive to muscles during gait and voluntary movement differs and supports that a locomotion specific spinal network contributes to plantar flexor muscle activity during human walking.

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.

Multi-segment foot model reveals distal joint kinematic differences between habitual heel-toe walking and non-habitual toe walking

Toe walking is observed in pathological populations including cerebral palsy, stroke, and autism spectrum disorder. To understand pathological toe walking, previous studies have analyzed non-habitual toe walking. These studies found sagittal plane deviations between heel-toe and toe walking at the hip, knee, and ankle. Further investigation is merited as toe walking may involve altered biomechanics at more distal joints, such as the midtarsal joint. The purpose of this study was to examine biomechanical differences between rearfoot strike walking (RFSW) and non-rearfoot strike walking (NRFSW) in the midfoot and ankle. We hypothesized that during NRFSW, midtarsal kinematics would diverge from those during RFSW in all three cardinal planes and ankle kinematics would display increased supination. Twenty-four healthy females walked overground with both walking patterns. Motion capture, electromyography (EMG), and force plate data were collected. A validated multi-segment foot model was used with mean difference waveform analyses to compare walking conditions during stance. Significantly different kinematics were found in all three planes for the midtarsal and ankle joint during NRFSW. The NRFSW midtarsal joint exhibited increased plantarflexion, eversion, and adduction with the largest differences occurring at initial contact and in the sagittal plane. The NRFSW ankle exhibited increased supination at initial contact and during early stance. These findings indicate that toe walking alters both distal and proximal foot joint kinematics in multiple planes. This may further the understanding of altered biomechanics during toe walking while providing a basis for future analyses of pathological gait.

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.