Pre-movement respiration-action coupling is specific to self-initiated action: Evidence for action alignment with ongoing breathing

Voluntary actions are coupled with the respiratory cycle, yet whether this coupling reflects action timing aligning with breathing or breathing adjusting to anticipated action remains unclear. This pre-registered study compared respiration-action coupling across three conditions using a modified Libet clock task. Thirty participants performed key presses under Self-initiated (freely chosen timing), Delayed (predictable timing after one full clock rotation), and Immediate (speeded response to stimulus onset) conditions. Circular uniformity tests revealed significant respiratory phase concentration at key press exclusively in the Self-initiated condition, and time-resolved phase consistency analysis showed that coupling emerged before movement onset only in this condition. These findings suggest that action timing aligns with ongoing breathing rhythms, and that temporal freedom, rather than preparation time or predictability, is critical for this coupling to emerge. Additionally, actions performed during inhalation were followed by shorter and deeper subsequent breaths across all conditions, indicating greater perturbation of ongoing breathing when acting during inhalation. Participants reported a subjective preference for pressing during exhalation, which correlated with individual differences in exhalation bias during self-initiated actions. Body awareness, but not interoceptive awareness or trait anxiety, predicted coupling strength. These results suggest that pre-movement respiration-action coupling reflects an implicit process whereby self-chosen action timing exploits ongoing respiratory states, potentially minimizing action-related respiratory perturbation.