Muscle Synergies Facilitate Computational Prediction of Subject-Specific Walking Motions.

Researchers have explored a variety of neurorehabilitation approaches to restore normal walking function following a stroke. However, there is currently no objective means for prescribing and implementing treatments that are likely to maximize recovery of walking function for any particular patient. As a first step toward optimizing neurorehabilitation effectiveness, this study develops and evaluates a patient-specific synergy-controlled neuromusculoskeletal simulation framework that can predict walking motions for an individual post-stroke. The main question we addressed was whether driving a subject-specific neuromusculoskeletal model with muscle synergy controls (5 per leg) facilitates generation of accurate walking predictions compared to a model driven by muscle activation controls (35 per leg) or joint torque controls (5 per leg). To explore this question, we developed a subject-specific neuromusculoskeletal model of a single high-functioning hemiparetic subject using instrumented treadmill walking data collected at the subject's self-selected speed of 0.5 m/s. The model included subject-specific representations of lower-body kinematic structure, foot-ground contact behavior, electromyography-driven muscle force generation, and neural control limitations and remaining capabilities. Using direct collocation optimal control and the subject-specific model, we evaluated the ability of the three control approaches to predict the subject's walking kinematics and kinetics at two speeds (0.5 and 0.8 m/s) for which experimental data were available from the subject. We also evaluated whether synergy controls could predict a physically realistic gait period at one speed (1.1 m/s) for which no experimental data were available. All three control approaches predicted the subject's walking kinematics and kinetics (including ground reaction forces) well for the model calibration speed of 0.5 m/s. However, only activation and synergy controls could predict the subject's walking kinematics and kinetics well for the faster non-calibration speed of 0.8 m/s, with synergy controls predicting the new gait period the most accurately. When used to predict how the subject would walk at 1.1 m/s, synergy controls predicted a gait period close to that estimated from the linear relationship between gait speed and stride length. These findings suggest that our neuromusculoskeletal simulation framework may be able to bridge the gap between patient-specific muscle synergy information and resulting functional capabilities and limitations

Insights into muscle metabolic energetics: Modelling muscle-tendon mechanics and metabolic rates during walking across speeds

Prior studies have produced models to predict metabolic rates based on experimental observations of isolated muscle contraction from various species. Such models can provide reliable predictions of metabolic rates in humans if muscle properties and control are accurately modeled. This study aimed to examine how muscle-tendon model calibration and metabolic energy models influenced estimation of muscle-tendon states and time-series metabolic rates, to evaluate the agreement with empirical data, and to provide predictions of the metabolic rate of muscle groups and gait phases across walking speeds. Three-dimensional musculoskeletal simulations with prescribed kinematics and dynamics were performed. An optimal control formulation was used to compute muscle-tendon states with four levels of individualization, ranging from a scaled generic model and muscle controls based on minimal activations, to calibration of passive muscle forces, personalization of Achilles and quadriceps tendon stiffnesses, to finally informing muscle controls with electromyography. We computed metabolic rates based on existing models. Simulations with calibrated passive forces and personalized tendon stiffness most accurately estimate muscle excitations and fiber lengths. Interestingly, the inclusion of electromyography did not improve our estimates. The whole-body average metabolic cost was better estimated using Bhargava et al. 2004 and Umberger 2010 models. We estimated metabolic rate peaks near early stance, pre-swing, and initial swing at all walking speeds. Plantarflexors accounted for the highest cost among muscle groups at the preferred speed and was similar to the cost of hip adductors and abductors combined. Also, the swing phase accounted for slightly more than one-quarter of the total cost in a gait cycle, and its relative cost decreased with walking speed.Comment: 33 pages, 7 figure

Effects of toe-out and toe-in gaits on lower-extremity kinematics, dynamics, and electromyography

Toe-in and toe-out gait modifications have received increasing attention as an effective, conservative treatment for individuals without severe osteoarthritis because of its potential for improving knee adduction moment (KAM) and knee flexion moment (KFM). Although toe-in and toe-out gaits have positive effects on tibiofemoral (TF) joint pain in the short term, negative impacts on other joints of the lower extremity may arise. The main purpose of this study was to quantitatively compare the effects of foot progression angle (FPA) gait modification with normal walking speeds in healthy individuals on lower-extremity joint, ground reaction force (GRF), muscle electromyography, joint moment, and TF contact force. Experimental measurements using the Vicon system and multi-body dynamics musculoskeletal modelling using OpenSim were conducted in this study. Gait analysis of 12 subjects (n = 12) was conducted with natural gait, toe-in gait, and toe-out gait. One-way repeated measures of ANOVA (p < 0.05) with Tukey’s test was used for statistical analysis. Results showed that the toe-in and toe-out gait modifications decreased the max angle of knee flexion by 8.8 and 12.18 degrees respectively (p < 0.05) and the max angle of hip adduction by 1.28 and 0.99 degrees respectively (p < 0.05) compared to the natural gait. Changes of TF contact forces caused by FPA gait modifications were not statistically significant; however, the effect on KAM and KFM were significant (p < 0.05). KAM or combination of KAM and KFM can be used as surrogate measures for TF medial contact force. Toe-in and toe-out gait modifications could relieve knee joint pain probably due to redistribution of TF contact forces on medial and lateral condylar through changing lateral contact centers and shifting bilateral contact locations

Simulated Development of Assistive Devices to Aid Older Adults in Ascending Stairs

Stair climbing is an important part of daily life. However, for older adults, stair climbing is one of the top five most difficult tasks, and the inability to climb stairs leads to a decreased quality of life. Assistive devices provide a way for people who cannot climb stairs to regain their mobility and improve their lives. While there are several assistive devices for climbing stairs on the market, assistive devices that use inexpensive elements like springs and assist joints like the knee and ankle have not been investigated. Simulations allow us to understand how assistive devices affect muscles during stair climbing and to test several variations of assistive devices before creating physical prototypes. In this study, I used OpenSim, software that models the human musculoskeletal system, to add ideal, massless torsional springs to simulations of individuals ascending stairs. Four healthy participants (4 female, age = 65.00 ± 4.76 years, height = 1.61 ± 0.02 m, weight = 58.59 ± 6.11 kg) provided IRB-approved written consent. Motion capture and electromyography data were previously collected and used to create individual models in OpenSim. Static Optimization (SO) was used to resolve the kinematics of the individuals into forces and activations. Metabolic cost was estimated from the SO activations and compared to an individual with no assistance. In addition, maximum forces produced by certain muscles while ascending stairs were compared with and without varying assistive devices. Overall metabolic cost increased for all spring stifffnesses and locations. The simulation of the unassisted individuals was the least metabolically expensive on average. However, two individuals had a decrease in overall metabolic cost when assisted at the ankle with a k =1 Nm/deg spring at the ankle, and one individual saw a decrease in metabolic cost when a k = 1 Nm/ deg spring was located at the hip. The vastus lateralis, vastus intermedius, vastus medialis, gluteus maximus, and soleus decreased in metabolic cost for all spring stiffnesses and for all joints. Overall, a spring with stiffness k = 1 Nm/deg located at the ankle was the least metabolically expensive spring simulated in this study, increasing the cost by 3 ± 11%. A spring with stiffness k = 5 Nm/deg located at the knee was the most metabolically expensive device, increasing overall cost by 1421 ± 421%. The results of this study can be used to further develop assistive devices to help older adults climb stairs and ultimately improve their quality of life.No embargoAcademic Major: Mechanical Engineerin

Changes in ankle work, foot work, and tibialis anterior activation throughout a long run

Background The ankle and foot together contribute to over half of the positive and negative work performed by the lower limbs during running. Yet, little is known about how foot kinetics change throughout a run. The amount of negative foot work may decrease as tibialis anterior (TA) electromyography (EMG) changes throughout longer-duration runs. Therefore, we examined ankle and foot work as well as TA EMG changes throughout a changing-speed run. Methods Fourteen heel-striking subjects ran on a treadmill for 58 min. We collected ground reaction forces, motion capture, and EMG. Subjects ran at 110%, 100%, and 90% of their 10-km running speed and 2.8 m/s multiple times throughout the run. Foot work was evaluated using the distal rearfoot work, which provides a net estimate of all work contributors within the foot. Results Positive foot work increased and positive ankle work decreased throughout the run at all speeds. At the 110% 10-km running speed, negative foot work decreased and TA EMG frequency shifted lower throughout the run. The increase in positive foot work may be attributed to increased foot joint work performed by intrinsic foot muscles. Changes in negative foot work and TA EMG frequency may indicate that the TA plays a role in negative foot work in the early stance of a run. Conclusion This study is the first to examine how the kinetic contributions of the foot change throughout a run. Future studies should investigate how increases in foot work affect running performance

Ankle Mechanical Impedance Under Muscle Fatigue

This paper reports preliminary results on the effects of ankle muscle fatigue on ankle mechanical impedance. The experiment was designed to induce fatigue in the Tibialis Anterior and Triceps Surae muscle group by asking subjects to perform isometric contractions against a constant ankle torque generated by the Anklebot, a backdriveable robot that interacts with the ankle in two degrees of freedom. Median frequencies of surface electromyographic signals collected from Tibialis Anterior and Triceps Surae muscle group were evaluated to assess muscle fatigue. Using a standard multi-input and multi-output stochastic impedance identification method, multivariable ankle mechanical impedance was measured in two degrees of freedom under muscle fatigue. Preliminary results indicate that, for both Tibialis Anterior and Triceps Surae muscle group, ankle mechanical impedance decreases in both the dorsi-plantarflexion and inversion-eversion directions under muscle fatigue. This finding suggests that decreasing ankle impedance with muscle fatigue may help to develop joint support systems to prevent ankle injuries caused by muscle fatigue.United States. Defense Advanced Research Projects Agency (Warrior Web Program BAA-11-72)Samsung Scholarship Foundatio

Ankle mechanical impedance under muscle fatigue

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 20-21).This study reports the effects of ankle muscle fatigue on ankle mechanical impedance. It suggests that decreasing ankle impedance with muscle fatigue may contribute to an increased probability of ankle injury. If confirmed, this observation may have important athletic, military and clinical implications. The experiment was designed to induce fatigue in the tibialis anterior and triceps surae muscle groups by instructing subjects to perform isometric contractions against a constant ankle torque generated by a backdrivable robot, Anklebot, which interacts with the ankle in two degrees of freedom. Median frequencies of surface electromyographic (EMG) signals collected from tibialis and triceps surae muscle groups were evaluated to assess muscle fatigue. Using a standard multi-input and multi-output stochastic impedance identification method, multivariable ankle mechanical impedance was measured in two degrees of freedom under muscle fatigue. Results indicate that ankle mechanical impedance decreases in both the dorsi-plantarflexion and inversion-eversion directions under tibialis muscle fatigue. However, the effect of triceps surae on ankle mechanical impedance is uncertain since the current experimental protocol could not effectively induce fatigue in triceps surae.by Shuo Wang.S.B

Muscle activations during functional tasks in individuals with chronic ankle instability: a systematic review of electromyographical studies

Background: It has been reported that individuals with chronic ankle instability (CAI) show motor control ab-normalities. The study of muscle activations by means of surface electromyography (sEMG) plays a key role in understanding some of the features of movement abnormalities. Research question: Do common sEMG activation abnormalities and strategies exists across different functional movements? Methods: Literature review was conducted on PubMed, Web-of-Science and Cochrane databases. Studies pub-lished between 2000 and 2020 that assessed muscle activations by means of sEMG during any type of functional task in individuals with CAI, and used healthy individuals as controls, were included. Methodological quality was assessed using the modified Downs&Black checklist. Since the methodologies of different studies were hetero-geneous, no meta-analysis was conducted. Results: A total of 63 articles investigating muscle activations during gait, running, responses to perturbations, landing and hopping, cutting and turning; single-limb stance, star excursion balance task, forward lunges, ball- kicking, y-balance test and single-limb squatting were considered. Individuals with CAI showed a delayed activation of the peroneus longus in response to sudden inversion perturbations, in transitions between double- and single-limb stance, and in landing on unstable surfaces. Apparently, while walking on ground there are no differences between CAI and controls, walking on a treadmill increases the variability of muscles activations, probably as a “safety strategy” to avoid ankle inversion. An abnormal activation of the tibialis anterior was observed during a number of tasks. Finally, hip/spine muscles were activated before ankle muscles in CAI compared to controls. Conclusion: Though the methodology of the studies herein considered is heterogeneous, this review shows that the peroneal and tibialis anterior muscles have an abnormal activation in CAI individuals. These individuals also show a proximal muscle activation strategy during the performance of balance challenging tasks. Future studies should investigate whole-body muscle activation abnormalities in CAI individuals

Experimental & Simulation Approaches to Study Neuromuscular Control in People with Chronic Ankle Instability

Ankle sprains are among the most common musculoskeletal injuries, and up to 70% of people who sprain their ankles develop chronic ankle instability (CAI). Moreover, people who develop CAI have a significantly higher risk of developing ankle osteoarthritis. Recent research has identified neuromuscular deficits that may be responsible for the high recurrence rates of ankle sprains and for the progression towards ankle osteoarthritis in people with CAI. Unfortunately, current rehabilitation strategies are not completely successful because the mechanisms responsible for these deficits are not fully elucidated. Therefore, the purpose of this dissertation was to investigate individual muscle forces and force generating capacities, the contributions of individual muscles to ankle joint contact forces, muscle activation patterns in the time-frequency domain, and central nervous system control strategies in people with CAI.Eleven people with CAI and 11 matched healthy control performed landing, anticipated cutting, and unanticipated cutting tasks, while three-dimensional movement, ground reaction force, and muscle activation data were collected with motion capture system, force plate, and electromyography, respectively. In the first study, a musculoskeletal model and static optimization were used to estimate the force and force generating capacity of individual muscles. In the second study, an additional joint reaction analysis was used in combination with the musculoskeletal model to estimate the contribution of individual muscle forces to ankle joint contact forces. In the third study, wavelet transformation and principal component analysis were used to analyze the time-frequency domain of muscle activation patterns. In the final study, non-negative matrix factorization was used to extract muscle synergies in order to identify central nervous system control strategies. Results from all analyses were compared between people with and without CAI.The primary findings of this dissertation were that, compared to healthy controls, people with CAI exhibit 1) greater muscle forces and/or force generating capacities in proximal muscles, 2) greater ankle anterior shear forces during early and late stance phases of unanticipated cutting, 3) lower intensity of muscle activation and a task-dependent inability to shift activation towards higher frequencies, and 4) similar complexity in neuromuscular control from a central nervous system perspective

Modular footwear that partially offsets downhill or uphill grades minimizes the metabolic cost of human walking

Walking on different grades becomes challenging on energetic and muscular levels compared to level walking. While it is not possible to eliminate the cost of raising or lowering the centre of mass (COM), it could be possible to minimize the cost of distal joints with shoes that offset downhill or uphill grades. We investigated the effects of shoe outsole geometry in 10 participants walking at 1 m s−1 on downhill, level and uphill grades. Level shoes minimized metabolic rate during level walking (Psecond-order effect \u3c 0.001). However, shoes that entirely offset the (overall) treadmill grade did not minimize the metabolic rate of walking on grades: shoes with a +3° (upward) inclination minimized metabolic rate during downhill walking on a −6° grade, and shoes with a −3° (downward) inclination minimized metabolic rate during uphill walking on a +6° grade (P interaction effect = 0.023). Shoe inclination influenced (distal) ankle joint parameters, including soleus muscle activity, ankle moment and work rate, whereas treadmill grade influenced (whole-body) ground reaction force and COM work rate as well as (distal) ankle joint parameters including tibialis anterior and plantarflexor muscle activity, ankle moment and work rate. Similar modular footwear could be used to minimize joint loads or assist with walking on rolling terrain