Relationship Between Physical Activity and Autonomic Responses in Adults with Type 2 Diabetes

Background: Cardiac autonomic dysfunction is a frequent complication of diabetes type 2 (T2DM). Heart rate variability (HRV) is a sensitive biomarker, but its relationship with habitual physical activity adjusted for metabolic and anthropometric factors remains underexplored. This study aimed to compare HRV indices between physically active and inactive adults with T2DM and assess the association between physical activity and clinical variables. Methods: In this cross-sectional observational study, 41 T2DM adults were classified as physically active (n = 22) or inactive (n = 19) using the short form of the International Physical Activity Questionnaire IPAQ-S. Resting HRV recordings were performed under standardized procedures. We analyzed the following time- and frequency-domain HRV indices: root mean square of successive heartbeat interval differences (RMSSD), standard deviation of normal-to-normal R-R intervals (SDNN), low-frequency (LF) and high-frequency (HF) power and their ratio (LF/HF). The analysis has been performed between-groups, and backward stepwise quantile regression examined the independent association of physical activity with HRV, adjusting for covariates. Results: Active participants exhibited higher HRV indices (SDNN p = 0.021; RMSSD p = 0.028; LF p = 0.032; HF p = 0.030), despite similar anthropometric and metabolic profiles. BMI correlated negatively with mean RR (ρ = −0.339, p = 0.030) and positively with mean HR (ρ = 0.339, p = 0.030). Physical activity was positively associated with LF (p = 0.015), and remained independently associated with SDNN (p = 0.021) and RMSSD (p = 0.048) after adjusting for HbA1c. Conclusions: Habitual physical activity was independently associated with enhanced autonomic modulation, with SDNN emerging as an early marker, supporting HRV as a biomarker for guiding exercise interventions in T2DM.