In collaboration with Gillette Children’s Specialty Healthcare, we evaluated whether muscle synergies change when unimpaired individuals walk at different speeds and slopes.
Background: The aim of this study was to determine whether changes in synergies relate to changes in gait while walking on a treadmill at multiple speeds and slopes. The hypothesis was that significant changes in movement pattern would not be accompanied by significant changes in synergies, suggesting that synergies are not dependent on the mechanical constraints but are instead neurological in origin.
Methods: Sixteen typically developing children walked on a treadmill for nine combinations (stages) of different speeds and slopes while simultaneously collecting kinematics, kinetics, and surface electromyography (EMG) data. The kinematics for each stride were summarized using a modified version of the Gait Deviation Index that only includes the sagittal plane. The kinetics for each stride were summarized using a modified version of the Gait Deviation Index – Kinetic which includes sagittal plane moments and powers. Within each synergy group, the correlations of the synergies were calculated between the treadmill stages.
Results: While kinematics and kinetics were significantly altered at the highest slope compared to level ground when walking on a treadmill, synergies were similar across stages.
Conclusions: The high correlations between synergies across stages indicate that neuromuscular control strategies do not change as children walk at different speeds and slopes on a treadmill. However, the multiple significant differences in kinematics and kinetics between stages indicate real differences in movement pattern. This supports the theory that synergies are neurological in origin and not simply a response to the biomechanical task constraints.
To estimate the impact of dynamic motor control on treatment outcomes in children with cerebral palsy.
We used multiple regression on a retrospective cohort of 473 ambulatory children with cerebral palsy who underwent conservative treatment, single-level orthopaedic surgery, single-event multi-level orthopaedic surgery, or selective dorsal rhizotomy. Outcomes included gait pattern, gait speed, energy cost of walking, and the Pediatric Outcomes Data Collection Instrument. Explanatory variables considered were pre-treatment levels of each outcome, treatment group, prior treatment, age, and dynamic motor control computed from surface electromyography using synergy analysis. Effect sizes were estimated from the adjusted response.
Pre-treatment levels had effect sizes 2 to 13 times larger than the next largest variable. Individuals with milder pre-treatment involvement had smaller gains or actual declines. Dynamic motor control was significant in all domains except energy cost. The effect size of dynamic motor control was second only to pre-treatment level, and was substantially larger than the effect size of treatment group for outcomes where both were significant (gait pattern 2:1, gait speed 4:1). The effect of dynamic motor control was independent of treatment group.
Dynamic motor control is an important factor in treatment outcomes. Better dynamic motor control is associated with better outcomes, regardless of treatment. PDF
The Ability & Innovation Lab is excited to announce that two of our recent grant proposals have been funded! This funding will help to accelerate our mission to improve movement for individuals with neurologic disorders.
Quantifying patient-specific changes in neuromuscular control in cerebral palsy: Funded by the National Institute of Neurological Disorders and Stroke, this research will examine how new measures of neuromuscular control can be used to better predict outcomes after multi-level orthopaedic surgery for individuals with cerebral palsy. We will be working in close partnership with Gillette Children’s Specialty Healthcare, one of the leading institutions in the management of pediatric neurological disorders. This research will address the challenge of identifying the best treatment for each individual. Cerebral palsy is caused by a brain injury and every brain injury is unique. We will be using new measures from muscle synergy analysis (see prior work here) to determine how patient-specific measures of control can be used to predict outcomes after surgery.
Ubiquitous rehabilitation to improve movement after neurologic injury:Funded by the joint NSF-NIH Smart & Connected Health Initiative, this research will work in partnership with the University of Texas at Austin to use flexible electrodes to track and train muscle activity after stroke and other neurologic injuries. We know that more practice and use after brain injury increases long-term recovery and function. This research will investigate new pathways for both motivating patients to re-learn to use their muscle and providing doctors and therapists with the data and insight needed to guide and customize therapy.
Kat Steele partnered with Mike Schwartz and Adam Rozumalski of Gillette Children’s Specialty Healthcare to complete one of the largest studies to date of individuals with cerebral palsy. They quantified how neuromuscular control is altered among individuals with cerebral palsy and how this altered control can contribute to impaired function.
Abstract: Individuals with cerebral palsy (CP) have impaired movement due to a brain injury near birth. Understanding how neuromuscular control is altered in CP can provide insight into pathological movement. We sought to determine if individuals with CP demonstrate reduced complexity of neuromuscular control during gait compared with unimpaired individuals and if changes in control are related to functional ability. Muscle synergies during gait were retrospectively analyzed for 633 individuals (age range 3.9–70y): 549 with CP (hemiplegia, n=122; diplegia, n=266; triplegia, n=73; quadriplegia, n=88) and 84 unimpaired individuals. Synergies were calculated using non-negative matrix factorization from surface electromyography collected during previous clinical gait analyses. Synergy complexity during gait was compared with diagnosis subtype, functional ability, and clinical examination measures. Fewer synergies were required to describe muscle activity during gait in individuals with CP compared with unimpaired individuals. Changes in synergies were related to functional impairment and clinical examination measures including selective motor control, strength, and spasticity. Interpretation: Individuals with CP use a simplified control strategy during gait compared with unimpaired individuals. These results were similar to synergies during walking among adult stroke survivors, suggesting similar neuromuscular control strategies between these clinical populations. PDF
Also, make sure you look at the commentary from Diane Damiano. She provides perspective about the utility of synergies for evaluating neuromuscular control in children with cerebral palsy and future challenges.
Kat Steele presented our recent work on altered synergies during gait in cerebral palsy and the impact of altered gait patterns at theInternational Society of Biomechanics conference on July 15, 2015 in Glasgow, Ireland.