This study examines the impact of guided breathing exercises on stress and heart rate variability (HRV) in autistic young adults. It explores how daily movement behavior (sleep, physical activity and sedentary behavior) influences HRV and to what extent two guided breathing exercises can affect HRV. Additionally, the study investigates how participants perceive the exercises in terms of usability and usefulness.

For many autistic individuals, transitioning into adulthood can be challenging and stressful. This stress often affects their mental health. The autistic community has highlighted the need for better mental health support, including accessible and effective ways to manage stress. Among the non-pharmacological interventions aimed at improving mental health via stress reduction, guided breathing interventions are promising, also on a psychophysiological level. During a stressful situation, internal regulatory processes take place to maintain balance, starting by activating the autonomic nervous system (ANS). Prior work indicates that a dysfunction of the ANS contributes to the heightened mental health challenges observed in autistic individuals. Heart rate variability (HRV), the variation in time between heartbeats, is an physiological index of the functioning of the ANS. The Neurovisceral Integration Theory highlights the role of parasympathetic regulation of the heart rate, associating higher vagally mediated HRV with better health, emotional regulation and executive functioning.In autistic individuals, the overall levels of cardiac vagal modulation are lower compared to neurotypical peers.

To date, research investigating the potential of interventions aimed at increasing HRV in autistic individuals is scarce. Moreover, HRV is influenced by several aspects (e.g., sleep, physical activity) and knowledge on their combined impact is necessary to understand how HRV can be used in research and clinical practice. Therefore, in this project, the investigators will explore the role of physical activity, sedentary behavior, and sleep on HRV and determine what constitutes a significant change in HRV.

The investigators will also examine the psychophysiological effects, feasibility, and acceptability of the two leading protocols in guided breathing interventions (heart rate variability biofeedback and slow-paced breathing). HRV-BF optimizes HRV by guiding individuals to breathe at their resonance frequency, synchronizing heart rate and breathing. SPB prescribes to breathe at a fixed pace of 6 breaths per minute.

Inclusion Criteria:

• For participants ≥18 years a voluntary written informed consent and for participants < 18 years a written informed consent from the parents or their legally authorized representative and an informed assent of the participant has been obtained prior to any screening procedures
• Male or Female (biological)
• Between 16 and 25 years old
• Diagnosis of autism as described in the DSM-IV/DSM-5(-TR)

Exclusion Criteria:

• Participant has a history of congenital heart diseases, diagnosed cardiovascular abnormalities or somatic diseases conditions that may interfere with the main outcome measure HRV or with the safe practice of breathing exercises (e.g., uncontrolled epilepsy, severe respiratory illness)
• Presence of contra-indications for participating (intervention and/or assessment): acute agitation and/or severe psychiatric symptoms (psychosis, mania or major depression) and/or active substance use.
• The presence of an intellectual disability, defined as an intelligence quotient < 70, as described in the DSM-IV/DSM-V.
• Insufficient knowledge of Dutch language in order to follow instructions and fill out questionnaires.
• Female who is pregnant.
• Participation in another interventional study, with or without an investigational medicinal product (IMP) or device (IMD).
• The use of medication known to affect cardiac modulation (excluding hormonal contraceptives).
• Hearing- or vision impairment that cannot be corrected to normal functioning.

Individual participant data (demographics, primary and secondary outcome measures, adverse events) will be shared. No directly identifying information will be included. The interview questions will be shared, but interview responses will not be made available in order to protect participant privacy.

The study protocol, the statistical analysis plan, analytic code, and a blank informed consent form will be shared. The de-identified dataset will be accompanied by clear documentation explaining the variables, coding, and outcome measures so that researchers can interpret the data without access to the full protocol or analysis plan.

IPD will be made available beginning 6 months after publication of the primary results and will remain available for at least 10 years.

De-identified individual participant data will be shared with qualified researchers for non-commercial scientific purposes. Requests must include a short proposal describing the planned analyses. Access will be granted following review by the principal investigator. Approved researchers will be required to sign a data use agreement prior to receiving access through the KU Leuven Research Data Repository.

The researcher plays an active role during the intervention, and participants will be informed about the different interventions provided in both groups.