Gait and Postural Balance Analysis During Head-motion Perturbed Standing and Walking in Older Adults

1. The CatchU® app quantitatively and objectively measures the ability to integrate visual-somatosensory information using reaction time test data. 2. Digit Symbol Substitution test assesses processing speed and attention by requiring individuals to match symbols with corresponding numbers within a specified time frame. 3. Trail Making Test part 1 and 2: assesses cognitive flexibility, visual attention, and task-switching by having individuals connect numbered circles in sequence (part 1) and then alternate between numbers and letters (Part 2). 4. Go/No Go test measures an individual's ability to inhibit a prepotent response (No-Go) and execute a response when required (Go). This test provides insights into executive functioning, particularly inhibitory control.

1. Cervical Sensorimotor control will be measured through a wireless wearable sensor 3D-cervical trainer by Sensamove on the placed on the head of the participant. The 3DCT registers cervical position sense by the Head Repositioning Accuracy test where the subject must relocate the head to the previously memorized (neutral) head position with the eyes closed and the joint position error degrees are registered. Cervical movement sense is examined using 'The Fly'-test where the subject ought to follow a movement pattern displayed on the screen in front of them. The movement of the neck-head unit is there upon tracked by the 3DCT and projected on the screen. 2. Vestibular function will be assessed through 3D-video Head Impulse Testing (vHIT), examining the state of the three semicircular canals by delivering the vestibulo-ocular reflex (vor) gain and vor gain asymmetry. 3. For the assessment of static and dynamic visual acuity, functional Head Impulse Testing (fHIT) will be used.

Frailty will be assessed using the Fried criteria, comprising 5 categories (each accounting for 1 point if scored positive): Unintentional weight loss (interview), weakness (grip strength with hand-held dynamometer), poor endurance and energy (two statements of the CES-D Depression Scale), slowness (walking speed over 15ft through gait analysis) and low physical activity level (Minnesota Leisure Time Activity questionnaire)(Fried et al., 2001).

Markers will be placed on the predefined anatomical locations and surface electrodes for electromyography will be applied at the predefined muscle locations following the SENIAM-guidelines. The Microsoft HoloLens 2 is fixated on the participant's head which will, on one hand, provide the cue to the participant for the head movement and on the other hand track eye and head movements. A safety harness is attached to the body and the ceiling of the lab. At the start of the trial, the subject will see a projection by the HoloLens 2 on the real environment moving to the left; right; upward; downward (cue in randomized order) which the participant is ought to follow with eyes and head. First while standing still and second while walking the 10-meter overground walkway at a self-preferred walking speed.

The researcher will visit the possible participants (at their home, community centre, etc.) and after written consent on screening procedure is provided, the tests for eligibility will be performed. 1. Interview: asking about age (years), gender (male/female), medical history and the number of falls in the last 12 months . 2. Timed Up-and-Go (TUG) to check walking ability. TUG is a sensitive and specific measure for identifying risk for falls (Shumway-Cook et al., 2000).

Participants are followed up for 12 months. They fill in a fall diary and telephone reminders will be performed monthly to encourage participants to complete and return their diaries.