# Investigating the Effect of Motion Capture Suits on the Test-Retest Reliability of Gait Parameters
###### Abstract  
When collecting marker-based motion capture data from clinical populations, speed of collection and comfort for the participant is a priority. This could be achieved by attaching markers to motion capture Velcro suits, as opposed to the skin. This study aimed to ascertain the reliability of sagittal-plane gait parameters estimated using Plug-in Gait (PiG) and Conventional Gait Model 2 (CGM2) marker sets from data collected in Suited and Non-suited (markers placed onto skin) conditions. For ten participants, markers were placed based on PiG and CGM2 models and data captured during a 2-min treadmill walk. Trials were repeated in suited and non-suited conditions. PiG ankle flexion/extension measurements had poor/moderate reliability (Non-suited ICC = 0.531, Suited ICC = 0.435). CGM2 ankle flexion/extension measurements had good/excellent reliability (Non-suited ICC = 0.916, Suited ICC = 0.900). There were significant differences in minimal detectable change (MDC) between conditions at the ankle for PiG (Non-suited MDC = 2.32\({}^{\circ}\), Suited MDC = 18.90\({}^{\circ}\)), but not for CGM2 (Non-suited MDC = 0.63\({}^{\circ}\), Suited MDC = 0.95\({}^{\circ}\)). When using CGM2, knee (Non-suited ICC = 0.878, Suited ICC = 0.855) and hip (Non-suited ICC = 0.897, Suited ICC = 0.948) showed good/excellent reliability in both conditions. A motion capture suit is not a reliable solution when collecting joint angle data using the PiG model but is reliable enough to consider when using the CGM2 model. motion capture; intraclass correlation; minimal detectable change; gait analysis; clinical biomechanics 22 August 2024  
18 September 2024  
1 Department of Biomedical and Clinical Sciences, Public Health and Sports Sciences Department, University of Exeter Medical School, Exeter EX1 2 HZ, UK 1  
[PERSON]  
2 Public Health and Sports Sciences Department, University of Exeter Medical School, Exeter EX1 2 HZ, UK 2  
with tape is not only time consuming but is associated with skin abrasion and rashes in older populations [5]. In addition, when taped to the skin, markers can fall off during dynamic tasks. MOCAP suits are used in the animation industry, where time efficiency is more important than anatomical accuracy. The suits are skin-tight and allow for markers to be attached via Velcro. The use of suits reduces the time taken to place markers and mitigates the risk of skin irritation associated with sticking markers to the skin. Therefore, these suits could be implemented in data collections, particularly when considering the feasibility of large-scale data clinical biomechanics studies with ageing and clinical populations [6]. Previous studies have used the kinematic data for ankle, knee and hip joints to investigate the possible causes of injury [7; 8] and track intervention and rehabilitation protocols [9]. The ankle, knee and hip joints provide essential roles in gait and are able to modulate their stiffness in response to changes in load or task, which in turn can be used to increase metabolic efficiency in gait [10]. Changes from distal (ankle) to proximal (hip) shifts in joint workloads have also been observed with advancing age, with older individuals producing more power for walking from the hips than younger adults, again increasing the metabolic cost of walking [11]. The use of motion capture data can aid in monitoring these changes. With objective data to compare across multiple timepoints and the ability to correlate discrete joint metrics with other quantitative and qualitative measures, this data is invaluable for bio-mechanists and clinicians. Therefore, methods such as the use of a MOCAP suit would seem logical as they increase the ease and reduce the time associated with data collection, significantly increasing the number of individuals that can be tested in a set time frame. However, the test-retest reliability of key gait kinematic parameters, such as ankle, knee and hip joint angles, when placing markers onto MOCAP suits is unknown.