Responders to Rhythmic Auditory Stimulation in Individuals Post-Stroke and Older Adults

Stroke is among the foremost causes of long-term disability worldwide. Though post-stroke neuromotor impairments are heterogeneous, they often result in reduced walking ability and physical activity, and a slow, asymmetric, and unstable gait. In the chronic phase of stroke, the persistence of walking impairment leads to subsequent declines in walking ability, setting off a cycle of disability and deconditioning, reduced mobility, and increased fall risk. The development and study of interventions that can improve walking ability after stroke has been identified as a top priority among patients, clinicians, and researchers, with the ultimate goal being the enhancement of independence and overall quality of life, and the mitigation of walking-related disability.

Stroke is a disease of aging, and older adults (OA) tend to walk more slowly and with a more variable walking pattern that is energetically more demanding. Similar to stroke survivors, the reduced function and quality of walking in older adults can lead to declines in walking ability, initiating a cycle of disability and deconditioning that increases the risk of injurious falls. Hence, maintaining walking function is crucial for preserving a high quality of life.

Rhythmic Auditory Stimulation (RAS) is a rehabilitation intervention that has shown promise for improving walking in both stroke survivors and older adults. Walking with RAS intervention has been proven to enhance walking function, particularly in terms of walking speed. RAS relies on the innate human capacity to synchronize movements with an external rhythm, such as walking to a regular auditory beat, a process referred to as auditory-motor entrainment. Rhythmic entrainment may stabilize gait patterns and reduce the metabolic cost of walking, as the body naturally selects a walking frequency that maximizes stability and minimizes energy expenditure. Moreover, rhythmic entrainment is thought to reduce the cognitive demand of walking, allowing individuals to allocate their attention to secondary tasks essential for safe community navigation. Despite the evidence supporting its effectiveness in improving walking speed and gait function, the biomechanical changes enabling these improvements are not well understood.

Furthermore, while RAS is an effective intervention, not everyone benefits from it equally. Individuals with stroke present with a wide variety of gait patterns, and the degree of gait impairment may influence the effectiveness of RAS intervention above and beyond any age-related changes. In this study, the investigators aim to identify predictors of the response to RAS intervention. More specifically, they seek to understand the association between baseline walking characteristics and the effect that RAS intervention has on walking ability.

For this analysis, the investigators define responders in three ways: (1) individuals who experience an increase in walking function, (2) individuals who see an improvement in gait quality, or (3) individuals who achieve enhancements in both gait quality and walking function while walking with personalized RAS.

The investigators hypothesize that post-stroke individuals with particular movement characteristics will exhibit increased walking distances and greater automaticity (i.e., reduced stride time variability) in the RAS condition compared to the baseline condition. Given that RAS promotes walking automaticity, the investigators anticipate that individuals with higher walking variability will derive the greatest benefit. Furthermore, investigators hypothesize that older adults with similar movement characteristics will also demonstrate increased walking distances and improved automaticity in the RAS condition compared to the baseline condition; however, it is expected that the effect size will be smaller in comparison to stroke survivors.

The investigators hypothesize that individuals who experience immediate improvements in walking function and/or gait quality while walking with personalized RAS are more likely to respond positively to long-term RAS intervention. However, the mechanism of action enabling this long-term response is expected to differ based on baseline deficits. The short-term, immediate responses to RAS measured in this study may provide insights into potential long-term mechanisms.

Study Protocol:

To assess the varied effects of RAS intervention, each participant will undergo a data collection session involving a series of population-specific clinical tests to characterize a sample of study participants. These tests include the Timed Up and Go (Stroke-specific), Functional Gait Assessment (Stroke-specific), Mini Balance Evaluation System (Older Adults-specific), Short Physical Performance Battery (Older Adults-specific), Mini-Mental State Examination (Older Adults-specific). In addition, all study participants will complete the 10-meter walk test (10MWT) at both a comfortable and fast walking speed and the 6-minute walk test (6MWT). Additionally, the 6MWT will be fully instrumented using motion capture cameras to track retro-reflective markers, wireless inertial measurement units, and force plates embedded in the walkway. These systems will enable simultaneous collection of gait kinematic, inertial, and kinetic signals, respectively. Metabolic measures will also be recorded during the 6MWT using indirect calorimetry.

Following the baseline 6MWT, participants will wear a custom, metronome-based RAS device. This device will employ a metronome application and bone-conducting headphones to provide auditory cues tailored to each participant based on a brief tuning procedure. Subsequently, the 6MWT will be repeated with RAS set to the patient-tailored metronome frequency.

The primary objective of this study is to assess the impact of personalized RAS on walking function (measured as the total distance covered in the 6MWT) and gait quality (evaluated by stride time variability) within each population group (stroke survivors and older adults). The investigators will also analyze RAS-induced changes in secondary gait quality metrics, including (1) the metabolic cost of transport, (2) ground reaction forces during walking, (3) joint kinetics, and (4) spatial-temporal gait parameter changes induced by varying distances. A secondary objective is to determine whether RAS-induced changes in walking function and/or gait quality are linked to specific baseline walking and gait impairment patterns (i.e., movement phenotypes) and whether these movement patterns are influenced by age.