Muscle Coactivation in subjects with Parkinson’s Disease: a Healthy-matched analysis of the Sub-Phases of Gait Cycle

Objective: To compare lower limb muscle coactivation (MC) during gait between Parkinson’s disease (PD) and healthy controls (HC). Background: MC increases with aging as a response to postural control deterioration [1]. While MC enhances static stability, it may reduce dynamic postural stability and movement efficiency [2,3]. negatively affecting gait and increasing fall risk [4]. Individuals with PD exhibits rigidity, bradikinesia and poor postural control [5] and these symptoms may be further exacerbated by MC. However, alterations of MC in PD are still unclear with conflicting findings [6-8]. Method: Subjects walked at self-selected speed on a 10m linear path. Muscle activity (5 muscles for lower limb) were recorded with surface EMG (Cometa ZeroWire). EMG data were normalized to peak activation, and integral was estimated to obtain the ‘area under the curve’ (AUC). Coactivation Index (CI) was then computed as: as 2*[(overlapping AUC of M1 and M2)/(AUC of M1 + M2)] for each couple of muscles [9]: Tibialis anterior (TA) vs Gastrocnemius medialis (GM), TA vs Soleus (SOL), Vastus Medialis (VM) vs Biceps Femoris (BF). Data between groups were compared using unpaired T test (SPSS). Results: Fifteen individuals with idiopathic PD (age: 63.4 ± 6.1 years; H&Y: 2.3 ± 0.6) and ten matched HC (age: 62.2 ± 7.6 years) were enrolled. Regarding CIs, no statistical differences were found between groups [Figure 1], despite that a qualitative comparison of EMG signals in specific sub-phases of gait cycle (GC) was performed. PD tended to show higher recruitment of both BF and VM during mid stance (MS: 10-40% of GC) with a sustained activation of VM during push-off (PO: 40-60% of GC) and an earlier and higher recruitment of BF [Figure 2]. During the first part of PO (40-50% of GC), PD appeared to have a higher recruitment of TA associated to lower activation of plantarflexors (GM and SOL). However, PD showed a higher and persistent recruitment of GM in early swing (ES:60-75% of GC) [Figure 3]. Conclusion: MC’s role in PD remains unclear, requiring further research. Our preliminary analysis highlights the importance of investigating muscle recruitment patterns and their interdependencies across specific gait cycle sub-phases as each requires distinct adaptations that may influence MC differently. A sub-phase-specific approach could provide a clearer understanding of MC compared to an overall gait cycle analysis. Background: MC increases with aging as a response to postural control deterioration [1]. While MC enhances static stability, it may reduce dynamic postural stability and movement efficiency [2,3]. negatively affecting gait and increasing fall risk [4]. Individuals with PD exhibits rigidity, bradikinesia and poor postural control [5] and these symptoms may be further exacerbated by MC. However, alterations of MC in PD are still unclear with conflicting findings [6-8]. Method: Subjects walked at self-selected speed on a 10m linear path. Muscle activity (5 muscles for lower limb) were recorded with surface EMG (Cometa ZeroWire). EMG data were normalized to peak activation, and integral was estimated to obtain the ‘area under the curve’ (AUC). Coactivation Index (CI) was then computed as: as 2*[(overlapping AUC of M1 and M2)/(AUC of M1 + M2)] for each couple of muscles [9]: Tibialis anterior (TA) vs Gastrocnemius medialis (GM), TA vs Soleus (SOL), Vastus Medialis (VM) vs Biceps Femoris (BF). Data between groups were compared using unpaired T test (SPSS). Results: Fifteen individuals with idiopathic PD (age: 63.4 ± 6.1 years; H&Y: 2.3 ± 0.6) and ten matched HC (age: 62.2 ± 7.6 years) were enrolled. Regarding CIs, no statistical differences were found between groups [Figure 1], despite that a qualitative comparison of EMG signals in specific sub-phases of gait cycle (GC) was performed. PD tended to show higher recruitment of both BF and VM during mid stance (MS: 10-40% of GC) with a sustained activation of VM during push-off (PO: 40-60% of GC) and an earlier and higher recruitment of BF [Figure 2]. During the first part of PO (40-50% of GC), PD appeared to have a higher recruitment of TA associated to lower activation of plantarflexors (GM and SOL). However, PD showed a higher and persistent recruitment of GM in early swing (ES:60-75% of GC) [Figure 3]. Conclusion: MC’s role in PD remains unclear, requiring further research. Our preliminary analysis highlights the importance of investigating muscle recruitment patterns and their interdependencies across specific gait cycle sub-phases as each requires distinct adaptations that may influence MC differently. A sub-phase-specific approach could provide a clearer understanding of MC compared to an overall gait cycle analysis.