Muscle synergies patterns as biomarkers for children and teens with type II spinal muscular atrophy

![CDATA[Rationale: Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder caused by degeneration of anterior horn cells in the spinal cord with loss of motor neurons and skeletal muscle atrophy, especially in the lower limbs. Proximal muscles are often weaker than distal muscles. Emerging evidence suggests that movement may be controlled by activation of discrete motor modules scaled by time varying coefficient. Here, we sought to compare the motor modules between SMA patients and healthy subjects during walking. Methods: Three SMA patients and 15 healthy adults were recruited to walk at their self-selected speed with recording of the surface electromyography of 14 lower-limb muscles. Muscle synergies were extracted by the non-negative matrix factorization algorithm for pairwise comparison between the two groups. Similarity between the muscle synergies bewteen groups was evaluated using the cosine of principal angles. Muscle synergies of each group were clustered by the k-means algorithm. Results: All SMA patients exhibited a synergy involving tensor fascia latae while normal adults did not exhibit it prominently. None of the SMA patients showed the adductor longus synergy, which was evidenced in the majority of healthy adults. Conclusions: Damage to the lower motor neurons in the spinal cord of SMA patients led to the emergence of two abnormal muscle synergies involving the muscles: 1) erector spinae, 2) hamstring, which were absent in healthy subjects. These suggested the recruitment of hip abductor that might lead to further atrophy of the hip adductor. These findings could guide exercise prescription and the development of relevant training protocol.]]