Dual Task Perturbation Training for OAwMCI

Studies have determined that compared to cognitively intact older adults (CIOA), older adults with mild cognitive impairment (OAwMCI) exhibit more pronounced balance and gait impairments which lead to an increased risk of falls and mobility decline. Such impairments are evident during dual-tasking (i.e., simultaneous performance of cognitive and motor task) and OAwMCI have demonstrated an increased cognitive-motor interference (deteriorated performance of either or both cognitive/motor task). Furthermore, our preliminary laboratory findings indicate that compared to CIOA, OAwMCI in response to large-magnitude treadmill perturbations exhibits poor reactive responses (first line of defense against balance loss) and are unable to modulate their responses as the magnitude of perturbation increases. Despite that conventional exercise methods offer beneficial effects; they comprise of self-initiated task-specific exercises and may not focus on training reactive responses. Additionally, due to the presence of subtle balance and gait deficits, clinical measures used may not be sensitive enough to determine the risk of fall post-training. Furthermore, these training methods incorporate multiple sessions due to which adherence to exercise training is difficult with only a fraction of the older adults benefiting from it. Therefore, it is essential to incorporate a task-specific strategy that promotes factors associated with falling like balance control, muscular responses, coordination of limbs, and cognition through which OAwMCI may acquire maximum benefits to prevent a balance loss. One feasible method, which harnesses technology that can be used to deliver balance disturbances either while standing or walking in a consistent and controlled manner, is via a custom-based motorized treadmill. The scientific rigor from preliminary studies has reported a successful reduction of falls through a single session exposing CIOA to multiple treadmill-induced perturbations during gait and has shown significant improvement in reactive responses. For that reason, this stage 1 pilot study will examine the feasibility, applicability, and tolerability of a combined cognitive, and perturbation training on biomechanical determinants associated with falls and promote physical activity: kinematic variables, muscular responses, and cognitive function.

Given the cognitive decline and poor reactive responses among OAwMCI, it is essential to incorporate a strategy to enhance cognition and motor performance for promoting healthy aging. For this reason, we propose this study that aims to determine the feasibility, applicability and tolerability of a dual-task perturbation training paradigm in OAwMCI. This involves a treadmill induced perturbation training while concurrently performing a cognitive task with an aim to improve effective compensatory stepping strategies to prevent balance loss. Further, while testing on laboratory induced perturbations may provide an insight into understanding kinematic variables, evaluating the change on performance-based outcome measure may be clinically useful. The overall aim of this proposal to examine the central mechanisms of reactive balance control and perturbation-training adaptation to improve fall-resisting skills in healthy older adults and people with MCI using the following set of aims. Aim 1: To examine biomechanical and neuromuscular differences during reactive balance control against mechanical perturbations during stance and gait between OAwMCI and CIOA. Compared to CIOA, OAwMCI will show: H1.1. greater falls due to impaired biomechanical (delayed step initiation, lower reactive stability and greater limb support descent) and neuromuscular responses (longer postural response latencies and fewer muscle synergies with different structural activation) on novel stance and gait perturbations, which will worsen with dual task performance; H1.2. reduced modulation (scaling) of biomechanical and neuromuscular responses with increasing perturbation intensity; H1.3. slower rate of adaptation in stability control and muscle synergy adjustment with repeated perturbation exposure.

Aim 2: To relate impairments observed during reactive balance control in perturbed stance and gait with structural brain integrity, cognition and falls in OAwMCI. These older adults will display H2.1: Lower gray matter volume in fronto-pareital cortex and brainstem, and lower white matter integrity in sensorimotor pathways which will significantly correlate with poor performance on reactive stepping response; H2.2: Lower scores on neuropsychological battery test and NIH cognitive toolbox examining domains of executive function (attention, cognitive flexibility and response inhibition), visuo-spatial awareness, episodic memory which will correlate with deteriorated reactive stepping response. H2.3: Fall-Index computed from measures of reactive stability and limb support that are obtained from perturbation-based reactive measures will better discriminate prospective laboratory induced and real-life falls than conventional instrumented (postural sway and limits of stability) and performance-based clinical measures of balance and mobility, with increased predictive accuracy of Fall-Index under dual-task conditions.

Aim 2: To determine if deficits in reactive balance responses contribute to increased falls in OAwMCI during static and dynamic tasks than CIOA especially under dual-tasking. H2.1: Measures of reactive stability and limb support under dual-task conditions during perturbed gait will best discriminate retrospective and laboratory induced falls in this population. H2.2 Predictive accuracy of Fall-Index which will be greater than of clinical measures of balance and mobility.

Aim 3: To examine the feasibility and potential effectiveness of novel 6-week perturbation-based cognitive-motor intervention for improving fall-resisting skills during perturbed stance and gait. H3.1: Post-training OAwMCI will improve stability control, cognition and reduced laboratory falls, especially under dual-task conditions. H3.2: Baseline cognition and structural brain integrity/connectivity will predict change in stability control and fall-risk. H3.3. Improvements in stability control, cognition and falls reduction will be retained for at least 3 months post withdrawal of intervention resulting in improved community ambulation and reduced fear of falling and perceived cognitive load on activities of daily living

Eligibility Criteria:
Inclusion Criteria:

* Age group: Older adults between the age group \> 55 years old with MOCA less than 26 out of 30 will be classified as mild cognitive impairment and those above 26 out of 30 as cognitively intact older adults .
* Absence of any acute or chronic neurological (Stroke, Parkinson's disease, Alzheimer's disease), cardiopulmonary, musculoskeletal, or systemic diagnosis.
* No recent major surgery (\< 6 months) or hospitalization (\< 3 months)
* Not on any sedative drugs
* Can understand and communicate in English
* Ability to walk more than 10 meters without an assistive device

Exclusion Criteria:

* Participants will not proceed with the study if any of the following occurs at baseline measurement: 1) HR \> 85% of age-predicted maximal heart rate (HRmax) (HRmax = 220 - age), 2) systolic blood pressure (SBP) \> 165 mmHg and/or diastolic blood pressure (DBP) \> 110 mmHg during resting), and/or 3) oxygen saturation (measured by pulse oximeter) during resting \< 90%.
* History of bone fracture or significant other systemic disease or surgery in the last six months
* Specific to MRI participants: Self-reported presence of a pacemaker, metal implants other than orthopedic implants, and/or Claustrophobia, cataract surgery (lens not compatible to the MRI confirmed by the MRI technician)
* Weighs \> 220 lbs (Harness weight threshold)