Inter-Limb Muscle Synergy of Hands-and-Knees Crawling in Typical Developing Infants and Infants with Developmental Delay.

The aim of this study was to quantify and compare the inter-limb muscle coordination during crawling between typically developing infants and infants with developmental delay. Typically developing (TD, $\text{N}=$20) infants and infants with at risk of developmental delay (ARDD, $\textbf{N}=$33) or confirmed developmental delayCDD, N=14) participated in this study. Surface electromyography of eight muscles from arms and legs and the corresponding joint kinematic data were collected while they were crawling on hands and knees at their self-selected velocity. The number of used inter-limb muscle synergies during crawling was identified by nonnegative matrix factorization algorithm. Our results showed that there was no significant difference in the number of used muscle synergies between ARDD and TD infants during crawling. However, a reduced number of synergies were identified in infants with CDD, as compared to that in TD and ARDD infants, indicating constrained neuromuscular control strategy during crawling in developmental delayed infants. The absence of inter-limb muscle synergies may be one of the mechanisms underlying the impairments of crawling in developmental delayed infants, who are at high risk of cerebral palsy. This result also suggests that the metrics of muscle synergy during infant crawling, such as the number of synergy, may be feasible as a biomarker for early diagnosis of infants with cerebral palsy.

Shoulder abduction-induced reductions in reaching work area following hemiparetic stroke: neuroscientific implications.

A stroke-related loss of corticospinal and corticobulbar pathways is postulated to result in an increased use of remaining neural substrates such as bulbospinal pathways as individuals with stroke are required to generate greater volitional shoulder abduction torques. The effect of shoulder abduction on upper extremity reaching range of motion (work area) was measured in 18 individuals with stroke using the Arm Coordination Training 3-D (ACT(3D)) device. This robotic system is capable of quantifying movement kinematics when a subject attempts to reach while simultaneously generating various levels of active shoulder abduction torque. We have provided data demonstrating an incremental increase of abnormal coupling of elbow flexion for greater levels of shoulder abduction in the paretic limb that results in a reduction in available work area as a function of active limb support. The progressive increase in the expression of abnormal shoulder/elbow coupling can be explained by a progressive reliance on the indirect cortico-bulbospinal connections that remain in individuals following a stroke-induced brain injury.

Source of work area reduction following hemiparetic stroke and preliminary intervention using the ACT3D system.

The effect of gravity increases the expression elbow/shoulder synergy patterns results in discoordination during movements following stroke. The Arm Coordination Training 3-D (ACT3D) robotic system is a novel way of recording movement patterns while a subject generates varying amounts of shoulder abduction torque. This system is used to provide preliminary data that show reduced elbow extension and shoulder flexion capabilities as shoulder abduction requirements increase resulting in reduced work area at high shoulder abduction levels. Single subject data is highlighted to illustrate the application of an intervention aimed at progressively training subjects to overcome the effects of abnormal joint torque coupling on reaching abilities.