Relationship Between Variability Of Posterior Lower Extremity Muscles And Speed In Individuals With Parkinson’s Disease

Abstract

BACKGROUND: Individuals with Parkinson’s Disease (PD) demonstrate progressive decreases in gait speed and difficulty with intralimb coordination when walking. Commonly, people with PD walk with reduced step length that may be associated with suboptimal activation of flexor muscles including the gastrocnemius and hamstrings. Individuals with PD often increase cadence to overcome reduced step length regardless of walking speed. Therefore, investigation of variability in locomotor muscles while walking overground may provide insight into walking behavior during community ambulation. PURPOSE: To determine associations between variability of lower extremity muscle activation and gait speed during the stance phase to swing phase transition in individuals with PD. Methods: Adults with idiopathic PD completed the 10-meter walk (10MW) overground at their preferred walking speed while on their anti-Parkinson’s medication. Surface EMG was placed bilaterally on the biceps femoris (BF), medial hamstrings (MH), and medial gastrocnemius (MG). Gait events (heel contact, toe off) were identified via lower extremity kinematics using a motion capture system. Coefficients of variation during (CV) during 50-60% of the normalized gait cycle, identified as terminal stance phase (tST) and 60-70% of the gait cycle, termed initiation of swing phase (iSW) were calculated for the three muscles. RESULTS: 9 adults (7M, age x[Combining Overline] =71.0, height x[Combining Overline] =172.2cm, weight x[Combining Overline] =78.0kg) walked overground (x[Combining Overline] =16 steps used in analysis), with an average gait speed of 1.12 ± 0.19m/s. Those with slower gait speeds (<1.1m/s), had a higher mean CV of MG activation during iSW (p=0.02). There was no difference between the CV of the MH, BF during tST and iSW. However, there was an interaction between gait speed and CV of the MH and BF with variability in the MG activation during iSW (p<0.01). Variability was primarily due to differences in duration, timing, and magnitude of activation for these muscles during each step. CONCLUSION: Uniformity of the timing and magnitude of muscle activation was related to gait speed in individuals with PD. Increased step to step variability of MG, BF, and MH activation and timing suggests a less stable gait pattern with functional consequences in people with PD.