Smart Sock for Monitoring Walking and Supporting Physical Activity in Older Adults

This study evaluates a low-cost, foot-worn sensing prototype and mobile application intended to support gradual walking activity in older adults. Many commercially available activity tools provide step counts or fixed goals but do not combine simple foot-level movement information, perceived effort, symptom reporting, and conservative progression rules. The proposed system is designed to explore whether a simpler and more accessible approach can be implemented reliably in community-dwelling older adults.

The smart sock is a removable research prototype used with ordinary footwear. Its sensing module combines an FSR402 force-sensitive resistor placed beneath the forefoot with the integrated inertial measurement unit in a Seeed Studio XIAO nRF52840 Sense board. The FSR402 is used to identify changes in foot contact, while the inertial sensor records patterns of acceleration and angular movement. These signals are used to derive step events, cadence, inter-step timing, and simple indicators of walking rhythm. The system is intended for activity monitoring and coaching only. It is not designed to diagnose disease, measure laboratory-grade plantar pressure, estimate oxygen consumption, predict falls, provide emergency alerts, or replace clinical assessment.

The prototype is built from readily available components to support reproducibility and low cost. It includes a protected 3.7-V lithium-polymer battery, a 3.3-kΩ 1/4-W metal-film resistor, flexible insulated wire, a small green perforated FR-4 prototype printed circuit board, and a removable protective enclosure. The FSR402 and resistor form a 3.3-V voltage-divider circuit connected to the analog input of the XIAO board. The board uses Bluetooth Low Energy to send session summaries to the mobile application. The electronics are enclosed and positioned above the foot or near the shoe laces; the sensor sits beneath the removable insole at the forefoot. The battery is not charged while the device is worn or inside the shoe.

The mobile application is designed specifically for older adults. Its interface uses large high-contrast text, clear icons, plain-language prompts, minimal navigation, optional audio prompts, and a direct method to pause a session or report a symptom. Rather than showing complex sensor graphs, the application provides a small number of understandable messages about the current walking plan, session completion, perceived effort, and whether the current level should be maintained, reviewed for cautious progression, or paused.

The progression approach is intentionally conservative. The application does not advance activity after a single successful session. It considers repeated session completion, perceived exertion within the intended range, absence of a reported fall or warning symptom, and the absence of concerning changes in the derived walking indicators. When conditions are favorable, only one part of the walking plan is changed at a time, such as a small increase in walking duration or a reduction in a planned recovery period. A report of pain, dizziness, unusual shortness of breath, a fall, high perceived effort, device discomfort, or a concerning walking trend leads to pausing, repeating, simplifying, or reviewing the plan rather than automatic progression.

The application includes an optional participant-controlled family-support function. If a participant chooses this option, a trusted family member or helper may receive limited practical notifications, such as that a session was completed, paused, or that a check-in may be helpful. The support person cannot see raw sensor information, perceived-effort ratings, symptoms, health history, functional-assessment results, or the application's progression rule. They cannot change the participant's settings, override an alert, or make a progression decision. This feature is intended to support encouragement and practical assistance while preserving participant autonomy and privacy.

The study will document whether the hardware, software, instructions, and monitoring workflow can be delivered as planned and whether the system produces usable information for a later, appropriately powered effectiveness study. Technical assessment will focus on agreement of device-derived step events and cadence with reference observations. Implementation assessment will consider wearable fit, battery and charging performance, data transfer, technical faults, ease of setup, device comfort, accessibility of the application, and acceptability of optional family support. Information collected by the application will be limited to data necessary for monitoring and evaluation, including time-stamped step events or derived features, session information, perceived effort, symptom reports, app status, technical logs, and selected family-support preferences. Data will be handled through institutionally approved, secure procedures.