DYNAMIC STABILTIY OF THE PARKINSONIAN GAIT Christopher J. Arellano, Ashley Hickerson, Melissa Scott-Pandorf, Vladimir Ivkovic and Max J. Kurz Laboratory of Integrated Physiology, Department of Health and Human Performance, University of Houston, Houston, TX, USA E-mail: carellano@uh.edu or mkurz@uh.edu, URL: www.hhp.uh.edu INTRODUCTION One of the hallmark features of Parkinson’s disease (PD) is its affect on gait. Individuals with PD often walk at a slower pace, have a shorter stride length and an increased amount of stride-to-stride variability (Morris et al, 1999). Many of these gait changes have been speculated to be strategies that attempt to prevent falls. However, 70% of PD patients experience an annual fall (Bloem et al., 2003). Despite the considerable amount of experimental work on the gait and postural balance of individuals with PD, clinical metrics that adequately measure fall susceptibility remains elusive. Recently, floquet analysis has emerged as a potential measure for quantifying fall susceptibility in the aging (Granata and Lockhart, 2008). Floquet analysis quantifies how disturbances or errors in the gait cycle are attenuated over many steps. A fall is more likely if it takes a longer time to correct the errors or disturbances that occur during the gait cycle. Historically, floquet analysis has been used extensively to determine the stability of walking robots (McGeer, 1990; Tedrake, 2004); however, its utility as a clinical measure of gait stability in humans remains for the most part unknown. The purpose of this investigation was to determine if floquet analysis discriminates between individuals with PD, who are susceptible to falls, and the young individuals, who have limited fall susceptibility. METHODS AND PROCEDURES Seven healthy young adults (height = 1.76 ± 0.07 m, weight = 77.61 ± 13.79 kg, age = 23.29 ± 2.21 yrs.) and seven individuals with PD participated in this investigation. Characteristics of the PD participants are detailed in Table 1. A six-camera motion capture system (200 Hz) was used to collect the right leg’s ankle, knee and hip joint sagittal plane kinematics as the subjects walked on the treadmill at a self-selected pace. All participants held onto the handrails while walking. The PD participants performed the walking trial while off their levodopa medication. A state vector (x) was created to evaluate the stability of the locomotive system. This vector was defined by the joint position and velocity of the hip, knee, and ankle at heel- contact. Floquet analysis was used to quantify the dynamic stability of the gait pattern (Granata and Lockhart, 2008). Table 1. PD participants’ characteristics. Age (years) 76.0+ 6.0 Height (meters) 1.74+ 0.1 Weight (kg) 71.9+ 12 UPDRS III 28.6+ 4.6 Hoehen & Yahr Score 2.8+ 0.7 Range of annual falls 0-30