Twenty-five participants will complete five weeks of heart rate variability biofeedback using emWave software (HeartMath®Institute, 2020). Participants will receive a weekly 30-minute heart rate variability biofeedback session for five weeks at the University Parkway Center, Brigham Young University. The heart rate variability biofeedback protocol will be based on Lehrer et al., 2013 and Yoo et al., 2022. This format will aid participants in implementing and learning breathing and heart rate variability biofeedback skills (Lehrer et al., 2020). All participants will wear an ear sensor to measure their pulse. The heart rate variability biofeedback will focus on autonomic balance through slow breathing at a resonance frequency of approximately 6 breathes per minute. The best approximate breathing pace for resonance frequency will be estimated and participant's resonance frequency will be provided and used for their homework and subsequent training sessions.

Twenty-five participants will complete five weeks of Osc-. Similarly, for the Osc- procedures, the client will be required to complete a five-week intervention. During the weekly session, participants will also be wearing an earlobe monitor with HeartMath. Participants will be administered the Scale of Positive and Negative Experience at the beginning of each session to assess for mood. Participants will also be administered the 3-item Rivermead Post Concussion Symptoms Questionnaire at the beginning of each session. Participants will be instructed that the purpose of this portion of the study is to decrease their breathing oscillations. A program was designed by Yoo and colleagues (2022) that gives feedback regarding a "calmness" score which reflects a better score (i.e., higher) when participants breath in a pattern that elicits less variability (i.e., less oscillations).

The first session of the HRVB intervention will focus on introducing the client to HRVB and calculating the participant's resonance frequency which typically range from 4.5-7 breaths per minute. Participants will first complete a five-minute baseline breathing condition. Following the breathing condition, the participants will complete five conditions for five minutes each. Specifically, each condition will have the person breath at 6, 6.5, 5.5, 5, and 4.5 breaths per minute with a minute break between. Session two will focus on practicing resonance frequency breathing and solidifying the correct resonance frequency for the participant. Additionally, this session will introduce the technique of breathing through pursed lips and abdominal breathing. For sessions three through five, participants will practice resonance frequency breathing and review previous strategies.

Test whether heart rate variability recovery following a stressor improves in individuals with mild traumatic brain injury following heart rate variability biofeedback

Examine whether heart rate variability increases at rest in individuals with mild traumatic brain injury from pre-treatment to post-treatment following heart rate variability biofeedback

The Rivermead Post Concussion Symptoms Questionnaire is a 16-item self-report measure of the severity of post-concussive symptoms following traumatic brain injury. The scale includes three categories of behavioral, physical, and cognitive symptoms, where participants are asked to rate the degree to which they experience 16 concussive symptoms in comparison to pre-injury symptoms within the past 24 hours. The items are rated on a 5-point scale from 0 (not experienced at all) to 4 (a severe problem). The RPQ-13 and RPQ-3 have good internal consistency and good test-retest reliability (0.89 and 0.72, respectively).