Muscle weakness has a limited effect on motor control of gait in Duchenne muscular dystrophy

Area of Science:

• Biomechanics
• Neuromuscular Physiology
• Movement Science

Background:

• Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle weakness.
• Muscle synergies, the coordinated activation patterns of muscles, are crucial for efficient movement.
• Understanding alterations in muscle synergies in DMD can provide insights into motor control deficits.

Purpose of the Study:

• To investigate if muscle synergy weights and activations differ in children with DMD compared to typically developing (TD) children.
• To determine if any observed alterations in muscle synergies are associated with muscle weakness in DMD.

Main Methods:

• Surface electromyography (sEMG) was recorded during gait in 22 children with DMD and 22 TD children.
• Muscle weakness was assessed using maximal voluntary isometric contractions (MVIC).
• Non-negative matrix factorization (NMF) was used to calculate muscle synergies, with differences analyzed using Mann-Whitney U and Hotelling's T2 tests.

Main Results:

• The average number of synergies explaining 90% of the variance (N90) was similar (three) in both groups.
• DMD participants showed altered weights in specific synergies (increased rectus femoris, decreased medial gastrocnemius).
• Synergy activations were largely similar between groups, with minor differences in combined activations during mid-swing; weakness was not correlated with these changes.

Conclusions:

• Muscle synergy weights and activations are largely preserved in children with DMD, despite significant muscle weakness.
• The findings suggest that non-neural factors may play a limited role in modifying muscle synergies in DMD.
• Further research is needed to elucidate the precise mechanisms underlying motor control in DMD.