Relationship between Heart Rate Variability and Functional Fitness in Breast Cancer Survivors: A Cross-Sectional Study

Background: Breast cancer is the most common malignancy among women worldwide. The treatments may also cause neuromuscular and skeletal disorders; therefore, the aim of this study was to verify the existence of a relationship between heart rate variability and different functional fitness parameters in women survivors of breast cancer. Methods: This cross-sectional study included 25 women survivors of breast cancer, with a mean +/- SD age, height, and body mass of 50.8 +/- 8.8 years, 1.6 +/- 0.7 m, and 67.1 +/- 12.3 kg, respectively. Patients underwent measurements of heart rate variability with time and frequency domain analyses, as well as a "30 s chair-stand test", "6 min walking test", "timed up and go test", and "ball throwing test". Results: A multiple linear regression analysis showed that from the heart rate variability frequency domain, high frequency explained 21% (R-2 = 0.21) of the "30 s chair-stand test" performance. Conclusion: The findings of this study highlight high frequency as a predictor of "30 s chair-stand test" performance, regardless of age and time after diagnosis, suggesting its usefulness as a clinical indicator of functionality in breast cancer survivors. This study presents a straightforward and non-invasive methodology predicting functional fitness in women breast cancer survivors potentially applicable to clinical practice.