The study design is a pragmatic feasibility trial comparing the effects of chiropractic maintenance care versus a control group, no chiropractic care, on heart rate variability (HRV) in healthy male adults. The subjects in both groups will be healthy controls as the purpose of the study is to determine beneficial effects, if any, of chiropractic maintenance care on physiological function as opposed to pain management. The theoretical framework suggests a potential role of chiropractic maintenance care in the prevention of segmental dysfunction in the spine and cascading neuro-endocrine responses to biomechanical stress of the spinal segments, hypomobility \[1, 2\].

Chiropractic maintenance care will be for a duration of 8 weeks with subjects scheduled for one visit per week. Control subjects will be asked to refrain from chiropractic care for 8 weeks. All subjects will be asked to maintain the current status of their lifestyle behaviors for the duration of the study period, e.g. do not change diet or exercise training schedules. Using the WHOOP wearable technology to record daily HRV, the primary outcome is the weekly average of HRV. There will be a baseline week of HRV recordings prior to starting the intervention phase of the study. An increase in HRV of at least 6.5% from baseline to 8 weeks without a concomitant change in the control group will provide preliminary insights on chiropractic maintenance care and regulation of autonomic nervous system functions. As this is a feasibility study to explore the utility of biometric devices to measure changes in HRV during chiropractic maintenance care, sample size is limited to 20 subjects.

The 20 subjects will be healthy male adults from 18 to 40 years old. Given the small sample size. females are being excluded to avoid any confounding effects of menstrual cycle on the measurement of HRV. The summary of the evidence to date indicates medium to large effects in fluctuations of HRV across the menstrual cycle \[3\]. The study design will include simple randomization of subjects into chiropractic maintenance care or control group. The intervention group will receive weekly chiropractic care, in the form of high velocity, low amplitude (HVLA) chiropractic adjustments delivered to restricted vertebrae of the cervical, thoracic and lumbar spinal segments. Motion palpation of the spine will be used to identify restricted vertebrae of the cervical, thoracic and lumbar spinal segments. Subjects in the intervention group who do not attend at least four (4) scheduled chiropractic visits will be withdrawn from the study. Subjects in the control group who receive more than two (2) chiropractic treatments (visits) will be withdrawn from the study. Subjects in either group who receive more than two (2) other complementary and alternative (CAM) therapies (visits) will be withdrawn from the study.

1. Kovanur Sampath K, Mani R, Cotter JD, Tumilty S. Measureable changes in the neuro-endocrinal mechanism following spinal manipulation. Med Hypotheses. 2015;85:819-24.
2. Sampath KK, Botnmark E, Mani R, Cotter JD, Katare R, Munasinghe PE, et al. Neuroendocrine response following a thoracic spinal manipulation in healthy men. J Orthop Sports Phys Ther. 2017;47:617-27.
3. Schmalenberger KM, Eisenlohr-Moul TA, Würth L, Schneider E, Thayer JF, Ditzen B, et al. A systematic review and meta-analysis of within-person changes in cardiac vagal activity across the menstrual cycle: Implications for female health and future studies. J Clin Med. 2019;8.