Are Modular Activations Altered in Lower Limb Muscles of Persons with Multiple Sclerosis during Walking? Evidence from Muscle Synergies and Biomechanical Analysis

Abstract

Background: Persons with Multiple Sclerosis frequently have gait deficits that lead to diminished activities of daily living. Identification of motoneuron activity patterns may elucidate new insight into impaired locomotor coordination and underlying neural systems. The aim of the present study was to investigate muscle synergies, identified by motor modules and their activation profiles, in persons with Multiple Sclerosis (PwMS) during walking compared to those of healthy subjects (HS), as well as, exploring relationship of muscle synergies with walking ability of PwMS.Methods: Seventeen PwMS walked at their natural speed while 12 HS walked at slower than their natural speeds in order to provide normative gait values at matched speeds (spatio-temporal, kinematic, and kinetic parameters and electromyography signals). Non-negative matrix factorization was used to identify muscle synergies from eight muscles. Pearson's correlation coefficient was used to evaluate the similarity of motor modules between PwMS and HS. To assess differences in module activations, each module's activation timing was integrated over 100% of gait cycle and the activation percentage was computed in six phases.Results: Fifty-nine% of PwMS and 58% of HS had 4 modules while the remaining of both populations had 3 modules. Module 2 (related to soleus, medial, and lateral gastrocnemius primarily involved in mid and terminal stance) and Module 3 (related to tibialis anterior and rectus femoris primarily involved in early stance, and early and late swing) were comparable across all subjects regardless of synergies number. PwMS had shorter stride length, longer double support phase and push off deficit with respect to HS (p < 0.05). The alterations of activation timing profiles of specific modules in PwMS were associated with their walking deficits (e.g., the reduction of Module 2 activation percentage index in terminal stance, PwMS 35.55 ± 13.23 vs. HS 50.51 ± 9.13% p < 0.05, and the push off deficit, PwMS 0.181 ± 0.136 vs. HS 0.291 ± 0.062 w/kg p < 0.05).Conclusion: During gait PwMS have synergies numbers similar to healthy persons. Their neurological deficit alters modular control through modifications of the timing activation profiles rather than module composition. These changes were associated with their main walking impairment, muscle weakness, and prolonged double support.

Motor primitives are determined in early development and are then robustly conserved into adulthood

“…Second, some synergies were not altered in weights but instead, ceased to be used strongly in patterns. Both of these types of changes are likely significant in motor drive infrastructure, pattern generation, and the pathologies and injury effects where synergies may have impact (27,(33)(34)(35)(36)(37)(38)(39)(40)(44)(45)(46)(47)(48)(49). Synergies normally weakly activated in intact CNS that become active in disease would interfere with normal function and be pathological.…”

Muscle Dysfunction and Walking Impairment in Women with Multiple Sclerosis

“…37 However, the participant pool represents a large range of walking functions and disability levels (EDSS score = 2.5-6.5), and measures of walking endurance and speed in the present study are similar to those previously reported for men and women with MS. 26,27 The medial gastrocnemius muscle was evaluated in the present study because of the critical role of this muscle in ambulation and its association with gait parameters. 38,39 Yet, note that many other lower extremity and trunk muscles contribute to ambulation, 39 and relationships between muscle function and walking ability may vary if assessed in different lower extremity muscles. In addition, muscle strength was evaluated during voluntary contractions, which can be influenced by both central and peripheral factors, so the observations related to strength cannot be solely attributed to peripheral mechanisms associated with skeletal muscle dysfunction.…”

Intra-Subject Consistency during Locomotion: Similarity in Shared and Subject-Specific Muscle Synergies

“…Muscle synergies during walking are generally extracted from a few gait cycles ranging from 1 ( Steele et al, 2015 ; Lencioni et al, 2016 ) to 20 gait cycles ( Kim et al, 2016 ). In most cases, synergies are computed by averaging or concatenating around 10 gait cycles ( Ivanenko et al, 2003 , 2004 ; Monaco et al, 2010 ; Chvatal and Ting, 2012 ; Coscia et al, 2015 ; Haghpanah et al, 2017 ).…”