The Impact Of High Intensity Interval Training On Fitness, Stress And Immunity In Breast Cancer Survivors

Objectives: The aim of this study was to explore the impact of exercise intensity on aerobic fitness and autonomic cardiac regulation (heart rate variability (HRV)) and salivary biomarkers of the stress systems (HPA-axis, cortisol; sympathetic nervous system, α-amylase) and mucosal immunity (secretory(s)-IgA), in breast cancer survivors. Methods: Seventeen participants (62 ± 8 years) were randomly assigned to; 1) high intensity interval training (HIIT; n = 6); 2) moderate-intensity, continuous aerobic training (CMIT; n = 5); or 3) a wait-list control (CON; n = 6) for a 12-week (36 session) stationary cycling intervention. Cardiorespiratory fitness (VO2peak), resting HRV and salivary biomarkers were measured at baseline 2-4 d pre-intervention and 2-4 d post the last exercise session. Results: A significant improvement (p ≤ 0.05) was observed for VO2peak in the HIIT group; 19.3% (B = 3.98, 95%CI = [1.89 ; 46.02]) and a non-significant increase in the CMIT group; 5.6% (B = 1.96, 95%CI = [-0.11; 4.03]), compared with a 2.6% (B = -0.64, 95%CI = [-2.10; 0.82]) decrease in the CON group. Post intervention improvements in HRV markers of vagal activity (log(ln)LF/HF, LnRMSSD) and sympathetic nervous system (α-amylase waking response) occurred for individuals exhibiting outlying (> 95% CI) levels at baseline compared to general population. Conclusion: HIIT (compared to CMIT and CON) improved cardiorespiratory fitness in breast cancer survivors. Non-invasive measures of the autonomic nervous system, stress systems and mucosal immunity should be explored further to understand the individualised responses to training adaptations within the breast cancer population.