Sit-to-stand-and-walk from 120% Knee Height: A Novel Approach to Assess Dynamic Postural Control Independent of Lead-limb

Abstract

Individuals with sensorimotor pathology e.g., stroke have difficulty executing the common task of rising from sitting and initiating gait (sit-to-walk: STW). Thus, in clinical rehabilitation separation of sit-to-stand and gait initiation-termed sit-to-stand-and-walk (STSW)-is usual. However, a standardized STSW protocol with a clearly defined analytical approach suitable for pathological assessment has yet to be defined. Hence, a goal-orientated protocol is defined that is suitable for healthy and compromised individuals by requiring the rising phase to be initiated from 120% knee height with a wide base of support independent of lead limb. Optical capture of three-dimensional (3D) segmental movement trajectories, and force platforms to yield two-dimensional (2D) center-of-pressure (COP) trajectories permit tracking of the horizontal distance between COP and whole-body-center-of-mass (BCOM), the decrease of which increases positional stability but is proposed to represent poor dynamic postural control. BCOM-COP distance is expressed with and without normalization to subjects' leg length. Whilst COP-BCOM distances vary through STSW, normalized data at the key movement events of seat-off and initial toe-off (TO1) during steps 1 and 2 have low intra and inter subject variability in 5 repeated trials performed by 10 young healthy individuals. Thus, comparing COP-BCOM distance at key events during performance of an STSW paradigm between patients with upper motor neuron injury, or other compromised patient groups, and normative data in young healthy individuals is a novel methodology for evaluation of dynamic postural stability.

Parameters that remain consistent independent of pausing before gait-initiation during normal rise-to-walk behaviour delineated by sit-to-walk and sit-to-stand-and-walk

“…Participants attended the gait laboratory once, and upon a visual cue after which they were instructed to move when ready, performed 10 rise-to-walk trials (5 STW and STSW trials) in a randomised order (at self-selected speed) leading with their non-dominant limb. Participants rose from an instrumented (pressure-mat, Arun Electronics Ltd, UK) height-adjustable stool (Svenerik, Ikea, Sweden) set at 120%KH (floor to dominant knee joint-line distance), with feet at bi-acromial distance and 10° of ankle dorsiflexion ( Fig 1 ) [ 14 ]. Participants walked forward 5m, stopped, and turned off the light at a switch to end the trial.…”

“…Kinematic data were acquired using an eight-camera optical motion analysis system (Oqus 3-series, Qualisys Medical AB, Gothenburg, Sweden) sampled at 60Hz and synchronised (1020Hz) with analogue data from 4 force plates (FPs) width 400mm, length 600mm mounted within the 5m walkway (9281E, Kistler Instruments AG, Switzerland), the stool pressure-mat, and light-switch. Two FPs were located under each foot to capture ground reaction forces (GRFs) during rising ( Fig 1 ), with two more positioned to capture GRFs up to step3 [ 14 ]. In the event participants did not interface with individual force plates cleanly, the trial was repeated.…”

“…Raw marker trajectories and GRF data were exported into Visual 3D software (C-Motion Inc., Germantown, USA) and smoothed with 10Hz and 25Hz 4 th order low-pass Butterworth filters respectively [ 14 ]. In order to establish step changes in light and pressure-mat analogue voltage signals necessary to determine light-on and seat-off events, they were filtered by 25-point window averaging.…”

Gait-initiation onset estimation during sit-to-walk: Recommended methods suitable for healthy individuals and ambulatory community-dwelling stroke survivors

“…After familiarisation in the gait laboratory, subjects were asked to perform STW and STS (in order to derive thresholds for the xGRFthresh method) on 5 occasions each, in a randomised order during one measurement session. On each occasion subjects followed a novel low-risk protocol, the details of which are published elsewhere [33]. In brief, subjects rose from an instrumented (300 mm diameter pressure-mat, Arun Electronics Ltd, Sussex, UK) stool set at 120% knee height, with their feet in a standardised position upon 2 force plates (9281e; Kistler Instruments Ltd., Hook, Hants, UK) with hands initially placed at a comfortable distance above thighs to avoid body marker obstruction (Fig 1).…”

“…As part of a wider study, a 3D whole-body marker set was used, which was defined by placing 40 reflective markers (Qualysis AB, Gothenburg, Sweden) on skin overlying anatomical landmarks. Body segments were tracked using an additional 31 markers mounted in accordance with a six degrees-of-freedom marker-set [33]. Kinematic data were acquired using 10 infrared cameras (Oqus-3, Qualysis AB, Gothenburg, Sweden) sampled at 60Hz and synchronised with the analogue output from the force plates and seat-mat (1020Hz).…”