Evaluation of Stress Intervention Performance and Usability of Smartwatch Guided Breathing Practice
Authors: Liu Shuyi , Rong Rong , Zhang Hanling 
Published: June 2024

Breathing practice is an effective method for alleviating mental stress. With the advancements in science and technology and the increasing demand for self-stress management, many mobile device based breathing practice applications have been developed. Based on the advantage of enabling multimodal breathing guidance, most commercial smartwatches are configured with breathing practice. However, current studies lack evaluation of stress intervention performance and usability for smartwatch guided breathing practice. In this study, we aim to explore which breathing guidance patterns and guided breathing frequencies for smartwatch-based breathing practice can effectively intervene with stress while ensuring a positive usability, and to make design recommendations for smartwatch-based breathing practice.Methods:Based on the investigation of the commonalities and characteristics of the breathing practice function settings of commercial smartwatches, we categorized the settings into one visual guidance pattern, two haptic guidance patterns, and three commonly used breath-guided frequencies. According to these guidance patterns, visual animation and haptic guidance prototypes were developed based on After Effects and Arduino. We used the Wizard of Oz method to implement visual and haptic guidance based on Apple Watch and Arduino, which can run independently or in concert.In the specific experimental phase, each participants completed a total of eight sets of experiments, including five guidance patterns and three breathing guidance frequencies. In each set of experiments, participants were required to complete a 1-minute mental arithmetic task as a stress input, a 1-minute breathing practice as a stress intervention, and to complete the Spielberger State-Trait Anxiety Inventory (STAI) and USE questionnaire to report subjective stress levels before and after the stress intervention and the subjective experience of using the stress intervention. Throughout the experiment, participants' heart rate variability (HRV) and respiratory rate (RR) were recorded using BIOPAC.Results: There was a significant difference between the stress state after the calculation task and the breathing practice. Regarding the breathing guidance patterns, the two haptic-only breathing guidance showed significantly lower usability, suggesting that haptics are more suitable for a supporting role in synergizing other patterns to guide the breathing practice. The breathing guidance that operates synergistically by visual and breath-like haptic guidance received the highest overall rating, possibly because this haptic feedback reduces cognitive workload by creating a natural mapping to the target action. In addition, acoustic feedback is considered as a developable smartwatch-based breathing guidance pattern. In terms of breathing guidance frequencies, the three commonly used deep breathing frequencies did not differ significantly in stress intervention performance and usability assessments, and individuals had different preferences for deep breathing frequencies. Therefore, personalizable and dynamic guidance frequencies might be a better solution.Conclusions:This paper analyzes the stress intervention performance and usability of smartwatch-guided breathing practice based on self-reported and objective physiological data, and proposes corresponding design recommendations for the breath-guided pattern and the guided breathing frequency. The findings of this paper could provide a reference for the design of the breathing practice function of smartwatches.