Combat Diver Training Shifts Autonomic Balance and Increases Vigor Without Cardiac Remodeling

Objective: To evaluate the effects of a six-month intensive combat diver training program on autonomic function, cardiac structure, and psychological mood.
Method: Seven elite male combat diver candidates (median age, approximately 23 years) were assessed before and after a six-month program incorporating static and dynamic apnea, freediving drills, and high-intensity aquatic conditioning. Heart rate variability (HRV) was recorded using a Polar H10 device and analyzed with Kubios software. Resting transthoracic echocardiography was performed in accordance with the American Society of Echocardiography guidelines. Mood was assessed using the validated Turkish version of the Brunel Mood Scale (BRUMS). The Wilcoxon signed-rank test was used for all comparisons.
Results: Training significantly increased parasympathetic tone, as demonstrated by a reduction in resting heart rate (from 68 to 62 bpm; p=0.045) and increases in RMSSD (from 43 to 57 ms; p=0.028), HF% (from 19.2% to 34.2%; p=0.018), and the PNS index (from −0.17 to 0.54; p=0.018), together with a marked decrease in the LF/HF ratio (from 4.20 to 1.92; p=0.018). All echocardiographic parameters remained unchanged (p>0.05). The BRUMS Vigor subscale score increased significantly (from 8 to 15; p=0.017).
Conclusion: Six months of combat diver training enhanced parasympathetic dominance and psychological vigor without inducing cardiac structural remodeling, suggesting improvements in operational readiness and resilience to stress.

Keywords: Heart rate, military personnel, military psychology, psychological resilience.