Sharif Digital Repository

Background: Muscle synergy is the leading hypothesis on how the central nervous system coordinates limb functions. Cerebral palsy (CP) patients utilize fewer synergies, and are believed to have a simpler neuromuscular control. This study was undertaken to determine whether consistent muscle synergies are recruited during ambulation in cerebral palsy crouch gait and how the muscles contribute to such synergies. Methods: Ten ambulatory CP patients were recruited. All walked with crouch gait. sEMG data were collected from 14 lower limb muscles during gait analysis. Non-negative matrix factorization method was utilized to extract muscle synergies. Results and significance: A total of five... 

It has been suggested that the central nervous system simplifies muscle control through basic units, called synergies. In this study, we have developed a novel target-matching protocol and used non-negative matrix factorization (NMF) technique to extract trunk muscle synergies and corresponding torque synergies. Isometric torque data at the L5/S1 level and electromyographic patterns of twelve abdominal and back muscles from twelve healthy participants (five females) were simultaneously recorded. Each participant performed a total number of 24 isometric target-matching tasks using 12 different angular directions and 2 levels of uniaxial and biaxial exertions. Within- and between-subject... 

The way central nervous system manages the excess degrees of freedom to solve kinetic redundancy of musculoskeletal system remains an open question. In this study, we utilise the concept of synergy formation as a simplifying control strategy to find the muscle recruitment based on summation of identified muscle synergies to balance the biomechanical demands (biaxial external torque) during an isometric shoulder task. A numerical optimisation-based shoulder model was used to obtain muscle activation levels when a biaxial external isometric torque is imposed at the shoulder glenohumeral joint. In the numerical simulations, 12 different shoulder torque vectors in the transverse plane are... 

Individuals with spinal cord injury (SCI) at lower thoracic levels might walk independently with the aid of mechanical orthoses and walker by using their unimpaired trunk and upper extremity muscles (TUEM). The required motor skills and the associated subtasks of the paraplegic locomotion, however, have not been well understood yet. The purpose of this study was to investigate the coordination of the TUEM activities throughout the paraplegic gait cycle using synergy analysis. For eight paraplegic individuals (30.6 ± 11.6 years; SCI level: T12), the kinematics data and the surface electromyography (EMG) signals of TUEM were recorded during 15 gait cycles. Non-negative matrix factorization... 

In this study the properties of muscle synergies, arising from optimal feedback control are investigated. Three different tasks namely reaching, via-point, and hitting are performed using optimization of corresponding cost functions. Then by applying non-negative matrix factorization method to a dataset of muscle tensions, synchronous muscle synergies are obtained. In this way, different muscle patterns can be generated by linear combination of these basis vectors with non-negative time-varying scaling coefficients. According to our simulations some of obtained muscle synergies are shared between tasks and some of them are specific for one task. This finding is also in agreement with the... 

Background: Lower limb amputation is a major public health issue globally, and its prevalence is increasing significantly around the world. Previous studies on lower limb amputees showed analogous complexity implemented by the neurological system which does not depend on the level of amputation. Research question: What are the differences in muscle synergies between healthy subjects (HS) and transfemoral amputees (TFA) during self-selected normal transient-state walking speed? Methods: thirteen male HS and eleven male TFA participated in this study. Surface electromyography (sEMG) data were collected from HS dominant leg and TFA intact limb. Concatenated non-negative matrix factorization... 

A hallmark of more advanced models is their higher details of trunk muscles represented by a larger number of muscles. The question is if in reality we control these muscles individually as independent agents or we control groups of them called "synergy". To address this, we employed a 3-D biomechanical model of the spine with 18 trunk muscles that satisfied equilibrium conditions at L4/5, with different cost functions. The solutions of several 2-D and 3-D tasks were arranged in a data matrix and the synergies were computed by using non-negative matrix factorization (NMF) algorithms. Variance accounted for (VAF) was used to evaluate the number of synergies that emerged by the analysis, which... 

The central pattern generators (CPG) in the spinal cord are thought to be responsible for producing the rhythmic motor patterns during rhythmic activities. For locomotor tasks, this involves much complexity, due to a redundant system of muscle actuators with a large number of highly nonlinear muscles. This study proposes a reduced neural control strategy for the CPG, based on modular organization of the co-active muscles, i.e., muscle synergies. Four synergies were extracted from the EMG data of the major leg muscles of two subjects, during two gait trials each, using non-negative matrix factorization algorithm. A Matsuoka׳s four-neuron CPG model with mutual inhibition, was utilized to... 

In spite of the extensive literature on the analysis of the muscle synergies during gait, the functionality of these synergies has not been studied in detail. This study explored the relationship between the motor modules and the kinematic maneuvers involved in human walking. Motion and surface electromyography data (of 28 trunk and lower extremity muscles) were acquired from ten healthy subjects during ten trials of self-selected speed gait each. The joint angle trajectories were half-wave rectified and divided into two independent positive directional degrees-of-freedom. The muscle and kinematic synergies were both extracted using the non-negative matrix factorization (NNMF) technique and...