Self-initiated Perturbation-based Training in Older Adults

Postural stability at the recovery steps after the perturbation will be calculated as the distance between the absolute center of mass (CoM) position in an anteroposterior direction relative to the closest edge of the Base of Support (BoS) normalized by foot length. The absolute CoM position and BoS position will be traced by the motion capture system synchronized with the force plates embedded underneath the slip-treadmill belts.

Generic balance ability will be assessed by the Brief-BESTest. Brief-BESTest can challenge balance across anticipatory postural adjustments, postural responses, sensory orientation and stability in gait, allowing for comprehensive examination of improvements that occur in reactive control. As a shortened version of the BESTest, the Brief-BESTest is an 8-item balance assessment containing 1 item for each of the 6 subsections of the BESTest.

Mobility will be assessed by Timed Up and Go test (in the unit of seconds).

The number of real-life falls in months after randomization will be recorded. Fall circumstances and related injuries will be required via phone contact. A fall is defined as an event resulting in a person unintentionally coming to rest on the ground or other lower level, not as the result of a major intrinsic event (e.g., syncope, stroke, or overwhelming hazard such as an earthquake).

Responsive postural adjustment upon translation will be assessed through Motor Control Test and Adaptation Test on a computerized dynamic posturography (Bertec® Balance Advantage® Dynamic system, Bertec® Corporation, Columbus, USA). During the Motor Control Test, participants will be requested to maintain their standing balance in response to 12 translations of the standing platform in either forward or backward direction with medium and large amplitudes. Weight symmetry, latency of reaction and amplitude of sway will be recorded. Full-body safety harness will be worn throughout the tests to protect the participants from any potential loss of balance.

Responsive postural adjustment upon tilting will be assessed through Adaptation Test on a computerized dynamic posturography (Bertec® Balance Advantage® Dynamic system, Bertec® Corporation, Columbus, USA). During the Adaptation Test, the force platform will either tilt up or down for a total of 10 repetitions. Sway energy will be recorded. Full-body safety harness will be worn throughout the tests to protect the participants from any potential loss of balance.

Dynamic balance will be assessed by Alternative Step Test (in the unit of seconds).

Balance confidence will be measured with the Chinese version of the shortened version of Activities-specific Balance Confidence Scale (ABC-6). The scale value is from 0 to 100, with higher values representing higher balance confidence.

Functional lower body strength will be assessed by Five-time Sit to Stand Test (in the unit of seconds).

Cognitive flexibility and executive function will be assessed by Trial Making Tests A and B (in the unit of seconds).

Participants will be exposed to one trip-like perturbation and slip-like perturbation on each foot at an unexpected time. The number of falls upon perturbations will be recorded.

Cognitive impairment will be assessed by Abbreviated Mental Test (AMT). AMT is a 10-item test, with a 10-point scale. A score less than 6 suggests a significant cognitive deficit.

Depressive symptoms will be assessed by Five-Item Geriatric Depression Scale. Participants will be asked to answer 5 questions as yes or no. The answer "no" for the first question and "yes" for the other four questions will be evaluated for depression.

Personality traits assessed by Ten-Item Personality Inventory. It has 10 items, each item adopts a 5-level score of 1 (Disagree strongly) to 5 (Agree strongly), and a higher dimension score indicates a stronger individual's personality proneness.

Generic preference-based quality-of-life will be assessed by five-level EuroQol five-dimensional questionnaire (EQ-5D-5L). The EQ-5D-5L essentially consists of 2 parts: the EQ-5D descriptive system and the EQ visual analogue scale (EQ VAS).

In the EQ-5D descriptive system, each dimension has 5 levels: no problems, slight problems, moderate problems, severe problems and extreme problems. Each health state is identified by a five-digit code, with 11111 representing the best and 55555 the worst possible health state.

In the EQ CAS, the scale value is from 0 to 100, with higher values representing higher balance confidence.

Muscle activations will be assessed by surface electromyography using an electromyography system (Trigno IM, Delsys Inc., Natick, MA, USA). Fourteen electrodes are placed bilaterally over erector spinae, rectus abdominis, gastrocnemius medialis, biceps femoris, rectus femoris, tibialis anterior, and gluteus medius according to the SENIAM guidelines (www.seniam.org) by the physical therapist.

Physical activity will be assessed by the Physical Activity Scale for the Elderly. This questionnaire will ask participants to recall their activity over the last 7-days. Activity types include sitting, walking, sport/recreation, exercise, occupational and household. A total score for physical activity can be calculated using these answers and the predetermined weights associated with each activity.