Autonomic and Hemodynamic Recovery After Mild Exercise Under Nasal-Only Versus Mouth-Only Breathing: A Randomized Crossover Study Using Wearable-Derived HRV

Background: Autonomic and hemodynamic recovery following exercise reflects cardiopulmonary resilience and is influenced by breathing patterns. Nasal and mouth breathing differ in airway resistance, ventilation efficiency, and autonomic modulation, yet their effects on post-exercise recovery remain unclear. Wearable-derived heart rate variability (HRV) enables non-invasive monitoring of autonomic dynamics in real time. This randomized crossover study examined how nasal-only versus mouth-only breathing influences autonomic and hemodynamic recovery after mild exercise in healthy adults.

Objectives: To compare the effects of nasal-only versus mouth-only breathing on heart rate recovery (HRR) and heart rate variability (HRV) kinetics following a standardized 3-minute step test in healthy first-year medical students, and to evaluate the feasibility of a wearable photoplethysmography (PPG) device (Amazfit Helio Strap) for autonomic field monitoring.

Methods: A randomized, counterbalanced crossover study was conducted in 50 healthy first-year MBBS students (25 males, 25 females; mean age 19.1 ± 1.0 years). Each participant completed two sessions separated by 48 hours: one with nasal-only breathing (mouth taped) and one with mouth-only breathing (nose clipped). Participants performed a YMCA 3-minute step test followed by 5 minutes of seated recovery. Heart rate and beat-to-beat intervals were continuously recorded using the Amazfit Helio Strap worn on the upper arm. Heart rate recovery at 1 minute (ΔHR₁min) and RMSSD were analyzed using paired statistical testing.

Results: Nasal-only breathing produced significantly faster autonomic recovery. One-minute heart rate recovery was greater in the nasal condition (26 ± 6 bpm) than the mouth condition (18 ± 7 bpm; p < 0.001). RMSSD during the late recovery phase (3–5 minutes) was significantly higher during nasal breathing (38 ± 9 ms) compared with mouth breathing (28 ± 8 ms; p < 0.001), indicating more rapid parasympathetic restoration. Seventy-two percent of participants were classified as high responders based on greater HRR during nasal breathing.

Conclusion: Nasal-only breathing significantly accelerates parasympathetic reactivation and cardiovascular recovery following mild exercise compared with mouth-only breathing. These effects are consistent with enhanced nasal nitric oxide delivery and improved baroreflex-mediated vagal activation. Wearable-derived HRV obtained from the Amazfit Helio Strap provides a feasible method for assessing recovery-phase autonomic physiology in field settings.