Interaction between respiration and central motor control in autonomic cardiac regulation

Adaptations in cardiac autonomic regulation induced by physical training are central to the health benefits of exercise. We investigated the interaction between central motor command, breathing rate, and expiration timing during an isolated joint movement. Fifteen volunteers (30.9 ± 7.2 years; 8 women) performed twelve 3-min leg extension tasks in a seated position under three randomized conditions: movement type (active vs. passive), breathing pattern (spontaneous, 12 or 6 cycles/min), and expiration timing (during extension vs. return). RR intervals and their variability were analyzed. Voluntary motor control reduced indices of autonomic and parasympathetic regulation (p < 0.05), whereas slow-paced breathing enhanced them. However, motor control exerted a dominant influence over cardiac autonomic regulation (p < 0.001), regardless of breathing rate. Expiration during the return phase was associated with greater parasympathetic activity (p < 0.05). These results highlight the central role of motor command in autonomic modulation and suggest that emphasizing expiration during recovery may help preserve parasympathetic regulation.