BrainFit was an observational cross-sectional study conducted in older adults that aimed to (i) assess acceptability, usability, and user satisfaction with the Xiaomi Mi Band 2® in Portuguese community-dwelling older adults in a real-world context; (ii) compare physical activity objective estimates obtained with the wearable activity tracker with data obtained from self-report questionnaires; and (iii) explore the associations between objectively measured PA and brain structure and function.

The results have shown that Xiaomi Mi Band® has an excellent level of acceptability, usability, and satisfaction among older adults, suggesting that this device is suitable for this population. Moreover, we found a large variation between subjective and objectively measured physical activity. Finally, the findings highlighted a positive correlation between physical activity, hippocampus volume, and higher functional connectivity.

Validation of a Wireless Bluetooth Photoplethysmography Sensor Used on the Earlobe for Monitoring Heart Rate Variability Features during a Stress-Inducing Mental Task in Healthy Individuals

Heart rate variability (HRV), using electrocardiography (ECG), has gained popularity as a biomarker of the stress response. Alternatives to HRV monitoring, like photoplethysmography (PPG), are being explored as cheaper and unobtrusive non-invasive technologies. We report a new wireless PPG sensor that was tested in detecting changes in HRV, elicited by a mentally stressful task, and to determine if its signal can be used as a surrogate of ECG for HRV analysis. Data were collected simultaneously from volunteers using a PPG and ECG sensor, during a resting and a mentally stressful task. HRV metrics were extracted from these signals and compared to determine the agreement between them and to determine if any changes occurred in the metrics due to the stressful task. For both tasks, a moderate/good agreement was found in the mean interbeat intervals, SDNN, LF, and SD2, and a poor agreement for the pNN50, RMSSD|SD1, and HF metrics. The majority of the tested HRV metrics obtained from the PPG signal showed a significant decrease caused by the mental task. The disagreement found between specific HRV features imposes caution when comparing metrics from different technologies. Nevertheless, the tested sensor was successful at detecting changes in the HRV caused by a mental stressor.