The Effect of Spinal Manipulative Therapy on Heart Rate Variability and Pain, and the Predictive Value of Conditioned Pain Modulation

Previously, Spinal Manipulative Therapy (SMT) was thought to mechanically affect the restoration of muscular and joint function, by normalising muscle tension and joint mobility. However, recent research has suggested that SMT may be influencing the incoming/ascending pain signals and/or the excitability of the central pain regulating mechanisms. People with chronic neck/shoulder pain have been found to have a disturbance of the Autonomic Nervous System (ANS). Little is known about the changes in the ANS and its relation to changes in pain in a series of treatments conducted in a clinical setting.

This multicentre randomized controlled clinical trial will be carried out in multimodal primary care clinics where both physiotherapists and chiropractors are consulted for musculoskeletal issues are selected to minimize selection bias from the patient's pre-desired treatment modality.

The subjects will be recruited among patients seeking care for persistent or recurrent Neck pain (NP), either self-selected or through referrals from general practitioners in the local areal. The aim is to study the effect of SMT and stretching exercises compared to stretching exercises alone, two well-known interventions for NP, during a two-week treatment regimen.

The primary outcome is the activity of the autonomic nervous system (Heart Rate Variability (HRV), but also Conditioned Pain Modulation (CPM) will be measured. HRV and CPM will be measured at baseline, prior to the third treatment and after the fourth treatment.

The subjective pain experience will be investigated by using two different instruments accessing pain intensity and the affective quality of pain, asked at the assessments during the two weeks of treatment and 2 months after the period of intervention ends.