To determine whether changes in neural control depend on wearing an orthosis during gait, a team of researchers measured the muscle activity and synergy of the lower-limb muscles. The results revealed that some muscle activities were significantly different among the three conditions.
Muscle activity during gait was measured in 15 healthy adults, and muscle synergies were extracted using non-negative matrix factorization. The participants walked on the treadmill at a comfortable speed, and the activity of eight lower limb muscles was recorded (rectus femoris, vastus medialis, gluteus medius, biceps femoris, semitendinous, tibialis anterior, lateral gastrocnemius, and soleus muscles).
Three experimental conditions were randomly conducted: walking without orthosis, walking with an AFO, and walking with a KAFO. The AFO and KAFO were selected from two types, medium and large, and all participants wore the orthosis on the lower left. A practice session was performed on the ground level before the measurement to determine the appropriate size, and any pain from the orthoses was assessed. All measurements were performed on a treadmill.
According to the study’s authors, walking with the AFO caused an increase in knee extension muscle tibialis anterior activity, while walking with the KAFO caused a reduction in gluteus medius activity. Tibialis anterior activity increased in the KAFO condition. No significant difference in the value of the number of synergies and dynamic motor control was observed, although the activity of muscle synergy tended to change with muscle activity. Knee extensor muscle activity related to the loading response was significantly increased by wearing the AFO. In the KAFO condition, hip abductor muscle activity related to weight bearing was significantly decreased, and ankle dorsiflexor muscle activity was increased to secure clearance during the swing phase.
However, the number of muscle synergies and complexity of muscle synergy did not significantly change among these conditions. Each muscle activity was changed by wearing the orthosis; however, the immediate mechanical constraint did not change the framework of muscle synergy.
“The results suggest that the presence or absence of orthosis did not influence the modularity of muscle synergy but changed the behavior of muscle synergy related to individual muscle activity,” the authors concluded.
The open-access study, “Effects of orthoses on muscle activity and synergy during gait,” was published in PLOS One.