Author(s): MULDER, J., OTTER-DROST, R., KIEFTE-DE JONG, J., ELFERINK-GEMSER, M., Institution: LEIDEN UNIVERSITY MEDICAL CENTER, Country: NETHERLANDS, Abstract-ID: 2343

INTRODUCTION:
Interoception, the perception of internal bodily signals, may play a key role in initiating, regulating, and maintaining physical activity. However, research on the relation between interoception and exercise mostly uses measures of interoception at rest while resting measures may not generalize to conditions under physiological load. Yet, assessment of interoception during progressive exercise remains understudied. The current study aims to address these gaps by assessing changes in interoceptive accuracy of heart rate and breathing frequency using a cardiopulmonary exercise test (CPET). As exercise intensity increases, interoceptive signals become more salient, but competing sensory and cognitive demands also increase. We therefore expect interoceptive accuracy to follow an inverted-U curve, improving from low to moderate intensities and then stabilizing or declining at high intensities.
METHODS:
Ninety-seven undergraduate students (63% female, age = 20.5 ± 1.4) from a human movement sciences bachelor's program at a Dutch university participated in the study. Heart rate (HR) and breathing frequency (BF) were assessed breath-by-breath during a CPET, which included one minute sitting stationary, three minutes warming-up, before workload increased. Interoceptive accuracy assessment during the CPET included estimation of HR and BF every three minutes, starting at minute one. Accuracy scores were on a scale from 0 to 1, with 1 being perfect accuracy. Two Linear Mixed Models (LMM) were specified with HR and BF interoceptive accuracy as outcome variables, continuous time as a predictor, random intercepts for each participant, and random slopes for time.
RESULTS:
Participants had a mean VO2max of 49.5 ± 8.1 mL/kg/min and a mean test duration of 14.9 ± 2.0 min. HR interoceptive accuracy increased progressively across timepoints from 0.79 ± 0.23 at minute one to 0.93 ± 0.07 at the end of the test, with a significant positive effect of time (b = 0.0085, SE = 0.0017, 95% CI = [0.0051, 0.0120], p < .001). BF accuracy fluctuated (minute 1: 0.58 ± 0.35; end of test: 0.67 ± 0.23) and showed no significant effect of time (b = 0.0028, SE = 0.0027, 95% CI = [-0.0025, 0.0080], p = .304). Interoceptive accuracy was significantly higher for heart rate (M = 0.861, SD = 0.078) than for breathing frequency (M = 0.602, SD = 0.237; t(85) = 9.94, p < .001).
CONCLUSION:
Contrary to hypotheses, interoceptive accuracy of heart rate and breathing frequency did not follow inverted-U curves during progressively increasing exercise intensities. Instead, heart rate interoceptive accuracy increased steadily throughout the CPET, approximating linear trends before plateauing toward the end of the test. In contrast, breathing frequency accuracy showed no consistent pattern and fluctuated across timepoints. These findings highlight the importance of assessing interoception during exercise rather than at rest and suggest relations between exercise intensity and interoceptive accuracy may be specific per bodily domain.