A total of 68 PD patients were enrolled in this study. These patients were diagnosed with PD according to the UK Brain Bank criteria.36 For forward and backward walking tests, five participants dropped out due to failure to perform the task or pain in lower limbs. Remaining participants were divided into freezer (n = 28) and non-freezer (n = 35) groups based on the presence or absence of FoG according to their responses to the new freezing of gait questionnaire (NFoGQ).37 In case of the turning test, a total of 57 PD patients participated in this study. Eleven participants dropped out due to failure to perform the task, pain in the lower limbs, and deteriorating condition in ‘off’ state (Fig. 2). These participants were further grouped as freezers (n = 25) and non-freezers (n = 32). Fourteen healthy elderly individuals also participated in this study as a control group.
Participants with any impairment of lower limbs within six months prior to the testing, those who had difficulty in walking unassisted, and those who exhibited musculoskeletal and neurological symptoms affecting gait were excluded. Inclusion criteria for this study were: diagnosis of idiopathic PD according to the UK Brain Bank criteria, mild-to-moderate stage of patients walking independently, currently taking stable anti-PD medications over six months, and no dementia, which was defined as a score of ≤ 24 on the Mini-mental state exam (MMSE).38 PD patients were tested at ‘defined off’ state. Experimental protocols were approved by the Institutional Review Board of Dong-A university Hospital and all methods were performed in accordance with the Declaration of Helsinki. All participants provided written informed consent prior to their participation in the study.
Forward and backward walking and turning tests were captured using six infrared cameras (Vicon, MX-T10, UK) on an 8-meter walkway, as in our previous study.27 A global coordinate system was established, with the positive X-axis to the right, positive Y-axis facing anteriorly, and the Z-axis defined as the cross-product between the X-axis and the Y-axis, with the positive Z-axis facing superiorly. Weight, height, shoulder offset, elbow width, wrist width, hand thickness, leg length, knee width, and ankle width were measured bilaterally for all participants to obtain joint kinematic data. A 39-marker plug-in-gait model with 14 mm spherical reflective markers placed according to the modified Helen Hayes marker set was used. Markers were attached on the clavicle, sternum, the 7th cervical vertebrae, the 10th thoracic vertebrae, scapular medial border, and bilaterally on the front and back of the head, shoulder, lower third of the upper arm, lateral humeral epicondyle, lower third of the forearm, medial and lateral styloid processes of the wrist, the 3rd metacarpal head, anterior superior iliac spine, posterior superior iliac spine, lower third of the lateral thigh, lateral femoral epicondyle, lower third of the lateral shank, calcaneus, lateral malleolus, and the second metatarsal head. These markers were secured with athletic tape to reduce motion artifacts. The sampling frequency for kinematic data was set at 100 Hz. Collected data were filtered using digital low-pass filters (second-order Butterworth filters) at 6 Hz. Motion data capture and post-processing of marker trajectories were performed using Nexus software (version 1.83, VICON, UK).
All participants performed forward and backward walking tests. They were asked to walk in forward and backward directions at their preferred speed. In case of 360° turning test, participants were asked to turn in left and right directions at their preferred speed. The start of turning was set as the pelvis rotation angle by 10° in the global coordinate system. The end of turning was set as the pelvis rotation angle by 350°. Three successful complete trials in forward and backward walking and turning tests were captured for each participant. Walking step was defined as two steps after the third step during the walking task. Each step and turning direction were divided according to more-affected side (MAS) and less-affected side (LAS). The control group exhibited a preponderance of right-hand dominance. Thus, the MAS for controls was taken to be the left side.
Spatio-temporal characteristics were analyzed using walking speed, step time, step length, stride time, stride length, and asymmetry index (AI) of step time and length during forward and backward walking. Additionally, total steps, total step time, walking speed, step time, step length, stride time, stride length, and AI of step time and length during turning were determined. AI was defined as observed asymmetry between MAS and LAS steps using maximum and minimum values of step time and length. The longest step time and length were considered as the maximum amplitude, whereas the shortest step time and length were taken as the minimum amplitude.25
Kinematic characteristics of walking was analyzed through RoM of lower limb joints, maximum anti-phase, and trajectory and area of 360o turning. RoMs of the hip, knee, and ankle in the sagittal plane were identified. RoM was calculated as the difference between the maximum and minimum joint angles during a single gait cycle. Toe clearance height was measured as the maximum vertical height of the toe marker during the swing phase of each step. The maximum anti-phase was calculated as the maximum angle between the pelvic vector (from left marker to right marker of the anterior superior iliac spine) and the shoulder vector (from left marker to right marker of the shoulder) in the horizontal plane during turning. Turning area, antero-posterior root mean square (AP-RMS) distance, and medio-lateral root mean square (ML-RMS) distance were calculated using the path of center of mass (CoM) during turning. Turning area was defined and calculated as 95% ellipse area of turning.39 AP- and ML-RMS distances were defined as diameters in AP and ML direction, respectively.
All statistical analyses were performed using SPSS version 21.0 (SPSS Inc., Chicago, IL, USA). Descriptive statistical analysis was utilized to describe characteristics of each variable using mean and standard deviation. Shapiro-Wilk test was used to confirm normality. Two-way repeated analysis of variance (ANOVA) was conducted to compare differences between groups and compare results within different steps or directions. In addition, Scheffe post-hoc test was used in one-way ANOVA between groups. T-test was conducted for paired samples between MAS and LAS steps in forward and backward walking tests and MAS and LAS direction in the turning test. For the association of NFoGQ and other symptom scales with spatio-temporal and kinematic variables during forward and backward walking and turning tests, Pearson correlation coefficient was used. Significance was set at p < 0.05.