Postural Control in Adults

Participants. All participants will sign written informed consent before their participation. The inclusion criteria are: 1) age 65 and above, 2) able to walk continuously for at least 10 min without assistive device, 2) have normal or corrected-to-normal vision. The exclusion criteria are: 1) neurological conditions such as stroke, Parkinson's disease, multiple sclerosis, brain tumor that significantly affect balance task and walking, 2) known peripheral neuropathy that influence sensation, 3) known vestibular dysfunction, 4) known cognitive impairments, 4) self-reported pain or musculoskeletal conditions that will significantly affect balance task and walking. Prior to enrolling in the study, the general purpose, procedures, and potential risks of the study will be explained to the potential participant and consent secured. Participants will be allocated to the no-V or the full-V group using a computerized random generator. The statistician will develop a randomization schedule and will issue it to the researchers before patient recruitment. Participants will be assigned to intervention groups using a block randomization scenario to keep the two groups even.

Baseline assessment. Demographic information will be collected in the 1st visit. Participants will complete questionnaires to record demographics and quantify physical activity level, quality of life, and psychological characteristics. Clinical outcomes regarding balance ability and proprioception assessment will also be performed. The information, surveys, and clinical outcomes collected at baseline assessments are listed in Table 1. Instrumentation. A stabilometer (Lafayette Instrument, Lafayette, IN, USA, Fig. 1) will be used for the training of the dynamic balance task. Outcome measures will be recorded in a motion analysis lab using force plates (AMTI, Watertown, MA, USA) for the center of pressure trajectory displacements. Intervention protocol. The experiment will take place over a 3-week period including screening and pre-intervention testing (1st visit), six dynamic balance training sessions (2nd to 7th visits), and post-intervention testing (8th visit). The six training sessions will be accomplished in 2 weeks. The dynamic balance training. The 2 weeks dynamic balance training involves standing and maintaining balance on a stabilometer, which consists of a platform (1.3m long by 1.4m wide) connected to a single axis that allows bidirectional sway (Lafayette Instrument Co.; Fig. 2). The maximum angular deviation of the platform is 18°. A safety harness may be provided to prevent falls but does not provide support during the performance of the task. Participants are required to maintain balance with feet in a medio-lateral orientation while standing on the balance board. A potentiometer monitors the sway angle of the platform. An integrated timer measures time in balance, which is defined as when the platform angle is within ± 5° of horizontal. The participants will be encouraged to maintain the platform in horizontal for as long as possible within a 30 s trial. Participants assigned to no-V group will perform the task with blind-fold.

Aim 1 Method Rationale. A critical component of gait, i.e. gait initiation, which is a destabilization process from static standing to continuous walking, provides an appropriate window to examine the integration of sensory and motor function. Compared to young adults, older adults demonstrate longer preparation time and reduced posterior displacement of center of pressure (CoP) trajectory as the individual prepares to accelerate the center of mass forward during gait initiation.21,22 Postural control during gait initiation are predictive of fall risk and have been used to examine the effects of selective interventions on sensorimotor integration during walking.38,39 This has direct clinical implications, as gait initiation is ecologically relevant to walking. Instrumentation. A force plate (AMTI, Watertown, MA, USA) will be used to capture the trajectory of the center of pressure during gait initiation. Procedures. Gait initiation will be performed at the pre-intervention and post-intervention testing. The participants will stand on a force plate with both legs, feet are should-width apart. The participant will be instructed to perform mathematic calculations (i.e. subtract seven consecutively from a three-digit number) and speak out the answers while standing on a force plate. The participants will be instructed to initiate walking while performing the cognitive tasks. They will be walking along a 7 m walk way as quickly as they safely can after a visual LED cue indicates the side of leg for gait initiation. The participant will be asked to continue walking for 3 m for one walking trial. Data processing and analysis. The posterior displacement of the center of pressure (CoP) will be measured by the displacement of the CoP trajectory from the initial CoP position to the maximum posterior position in the anterior-posterior direction (Fig 3). Expected outcomes. After 2 weeks of the dynamic balance training, The investigators expect to see a greater increase in the posterior displacement of the CoP trajectory during gait initiation in the no-V group (Fig 4).

Aim 2 Method Rationale. The Modified Clinical Test for Sensory Interaction on Balance (CTSIB-M) is used clinically for balance analysis and to determine the dependence of the individual on all sensory systems (i.e. vision, vestibular and somatosensory) during balance tasks. The CTSIB-M has been shown to have excellent reliability in older adults and predictive to future fall incidence 40,41. Procedures. To perform the CTSIB-M, the participants stands with their hands at their side with the goal to stand as steady as possible for 30 s, under four different conditions (i.e. stand on firm surface with eyes-open, stand on firm surface with eyes-closed, stand on compliant surface with eyes-open, stand on compliant surface with eyes-closed). The investigators will collect three trials in each condition. Each trial will be timed with a stop watch, and the timer stops when the participant moves their arms, shows more than minimal body sway, and lose their balance or take a step. The test will be carried out on a force plate which will record the center of pressure trajectory for a secondary quantitative analysis regarding the amplitude of body sway. Data processing and analysis. The time in balance of the four conditions will be compared pre- and post- intervention using repeated measures ANOVA. Expected outcomes. The investigators expect that the no-V group will show improved time in balance in the "stand on firm surface with eyes-closed" condition which focuses on to evaluate the contribution of somatosensory inputs during the standing balance task.