Beyond 0.1 Hz: Distinct affective and cardiac responses to slow and super-slow-paced breathing

0.05 Hz super-slow-paced breathing, beyond the well-known slow-paced 0.1 Hz rate, may induce distinct psychophysiological effects through differentially modulating body-brain pathways. To address this gap, we assessed respiratory heart rate variability (RespHRV), root mean square of successive differences (RMSSD) and affective responses during 0.05 Hz and 0.1 Hz breathing. Fifty-three participants (49% female; Age: M = 24.13 years) performed both breathing rates in randomized, counterbalanced order following a baseline condition, with each phase lasting 5 min. Peak-valley RespHRV increased with decreasing breathing rate, highest at the 0.05 Hz rate, followed by 0.1 Hz, and lowest at baseline. Although yielding a similar direction, no significant differences emerged for frequency-domain RespHRV. In contrast, RMSSD was highest during 0.1 Hz and comparable between 0.05 Hz and baseline. 0.1 Hz breathing yielded broader affect modulation, reducing negative and positive affect-primarily the "Activation" subfacet-while increasing fatigue, whereas the 0.05 Hz pace selectively reduced negative affect. Thus, slow and super-slow-paced breathing induced different psychophysiological effects. Specifically, 0.05 Hz breathing preferentially enhanced RespHRV, emphasizing the peak-valley method as a robust indicator, while 0.1 Hz breathing exerted stronger affect modulation. These findings suggest the importance of considering breathing frequency-slow- versus super-slow-paced-when targeting affect regulation and cardiac entrainment.