Muscle Interactions during Gait in People with Parkinson’s Disease

Objective: To study modulation and asymmetry in lower limb muscles in individuals with Parkinson’s Disease (PD), compared to healthy controls (HC). Background: Walking disorders are among the most disabling symptoms in individuals with PD[1]. Reduced postural control and an increased risk of falling are associated with alterations in muscle activation during gait in PD[2], but the extent of these differences remains poorly understood. To quantitatively investigate muscle activity—specifically modulation and asymmetry—, various indices have been used in PD[3] and other populations[4,5]. Method: Subjects with idiopathic PD and matched controls were asked to walk along a linear path at a self-selected speed. A motion captures system (Qualisys), synchronized with 14 surface EMG sensors (Cometa Zero Wire) collected data on the bilateral activity of seven muscles of the lower limb. Muscle activity was quantified using the area under the curve of the EMG envelopes during the gait cycle, normalized to the peak activation across trials. The modulation index – MI=(EMGmax-EMGmin)/EMGmax – was calculated for each muscle and averaged between sides. The asymmetry index – AI=|1-(EMGright/EMGleft)| – was computed for muscles on opposite side for each subject. Overall MI and AI, averaged across all the muscles, were then computed and compared between groups. The values of both indices ranged from 0 to 1, with higher MI values indicating better modulation and higher AI values indicating greater asymmetry. Both indices were compared between groups using t-test or U Mann-Whitney, depending on data distribution. Results: Fifteen individuals with PD (age:63,40±6,06 years old; UPDRS:33,6±12,29; H&Y:2.27±0.59) and ten HC (age:62,20±7,60 years old) were compared. A significant reduction in the MI of the medial gastrocnemius [Figure1] (MD:-0.049, CI:-0.002;-0.096; p:0.042) and an increase in the AI of the rectus femoris [Figure2] (MD:0.142, p:0.016) were found. Overall MI was lower in PD (MD:-0.011; CI95:-0.040;0.017; p: 0.41) and overall AI was higher (MD: 0.046; CI95:-0.023;0.115; p:0.18), though the differences were not statistically significant. Conclusion: A reduction in MI and an increase in AI were found in PD, respectively for gastrocnemius medialis and rectus femoris. The use of indices may help personalize rehabilitation, but further studies are needed to delve deeper into the mechanisms underlying gait in PD, especially with regard to muscle activity.