Abstract
Breast cancer survivors (BCS) frequently experience increased Fear of Falling (FOD), which restricts physical activity and compromises functional independence. While High-Intensity Interval Training (HIIT) is recommended to improve cardiorespiratory fitness and reduce cancer-related fatigue, its acute physiological stress may disrupt sleep architecture, potentially exacerbating FOD.
This study investigated the day-to-day correlation between qualitative sleep parameters (measured by a smartwatch) and FOD intensity in post-HIIT days in a breast cancer survivor.
A longitudinal case study was conducted over four weeks with a 73-year-old female survivor. Sleep metrics (efficiency, deep sleep, awakenings) were objectively tracked using an Apple Watch Series 6, while FOD was assessed daily using the Falls Efficacy Scale-International (FES-I). Data were analyzed using Pearson correlation coefficients.
Results indicated a significant negative correlation between sleep efficiency and FOD (r=−0.65,p<0.01). Days with sleep efficiency below 75% showed significantly higher FOD scores (Mean = 32) compared to days with efficiency above 80% (Mean = 24). Furthermore, HIIT interventions led to improved resting heart rate and reduced RPE, coinciding with a gradual decline in FOD from 28.5 to 23.8 over four weeks.
These exploratory findings suggest that sleep quality, particularly sleep efficiency, may be associated with FOD intensity in breast cancer survivors. The results highlight the potential value of personalized HIIT protocols, which account for daily sleep recovery status, in supporting psychological safety and physical engagement. Integrating wearable technology into clinical rehabilitation may allow for real-time adjustment of training loads to optimize both physiological adaptation and psychological well-being in this vulnerable population.