RR-PL-0516

Monday 15:40, Palau de Congressos, Hall 2, Room A

ANALYSIS OF SIT TO WALK: DEFINITION OF MOVEMENT PHASES. Kerr A, Kerr K.M, Durward B; Glasgow Caledonian University and University of Nottingham, UK PURPOSE: Walking can be initiated from a variety of positions and postures. Walking from sitting is one of the most common movement sequences and yet sit to walk (STW) is rarely investigated. Sit to stand (STS) has been deconstructed into distinctive phases based on kinematic and kinetic data. A similar approach is proposed for STW. This study aims to define, measure and test consistency of phases of STW. RELEVANCE: STW is an inherently more unstable task than STS, demanding greater movement of the centre of mass (CoM). As well as presenting a falls risk there is a likely increased demand on the musculoskeletal system. Characterising the movement by phases will improve understanding of this everyday movement, ultimately informing rehabilitation and falls prevention. SUBJECTS: Thirteen normal healthy subjects with a mean age of 39.8 years, weight 80.9kg and height 1.76m were recruited from staff and students of the University of Nottingham. METHODS: Subjects  sat on a stool adjusted to knee height, ankles in neutral with feet resting, in parallel, on a single forceplate. Active markers were placed over anatomical landmarks to define four segments in the saggital plane (trunk, thigh, leg and foot). Following a familiarisation period subjects performed (x5) STS and STW at customary speed with arms crossed. Kinetic and kinematic signals were sampled for 5 seconds at 200Hz. ANALYSIS: Notable events were identified from the motion analysis (CODA ®) and force plate signals and used to distinguish phases. Mean and standard deviation of event timings and phase durations were calculated relative to movement initiation. Within subject consistency was tested using the intraclass correlation coefficient (ICC). RESULTS: Six events were identified: Initiation- first time vertical force (Fz) exceeds (>2 SD) the mean Fz measured during quiet sitting, Seat off- peak Fz, Peak Umom- peak upward velocity of the CoM, Gait initiation- first time mediolateral force exceeds 5.6% of body weight, Swing toe off- time of peak lateral velocity of the centre of pressure toward stance foot and Stance Toe off- time when Fz=0. This defined four phases; phase 1“flexion momentum” (initiation-seat off) lasting 0.81s +/- 0.06 (47.5% of total), phase 2 “extension” (seat off-peak Umom) lasting 0.26s +/-0.06 (15.3% of total), “unloading” (gait initiation-swing toe off) lasting 0.36s +/-0.07 (21.1% total) and “stance” (swing toe off-stance toe off) which lasted 0.56s +/- 0.07 (32.9% total). Overlapping between phase 2 and 3 accounts for the sum of  phases exceeding 100%. ICC values for phase duration were; 0.66 (flexion momentum), 0.54 (extension), 0.60 (unloading) and 0.81(stance). CONCLUSIONS: Four phases of STW were defined from force and movement data. There was good, within subject, consistency for phase duration. This is the first study to describe phases of STW and test their consistency. These findings provide a framework for studying this everyday movement.