the clinical criteria for the diagnosis of MTrPs in this study were adapted from those specified by Travell and Simon (1983). Participants were included if they presented with chronic back pain, which had lasted longer than 12 weeks, and had at least one trigger point in the upper and/ or lower back region. Trigger points were diagnosed as the presence of spot tenderness in areas that the patient identified as painful.
the criteria for exclusion from the study was based on any history of disease or other disorder, which may effect heart rate variability (HRV); such as myocardial infarction, hypertension, neuropathy diabetes mellitus, fever, a history of acute trauma, spinal fracture, inflammatory arthritis (rheumatoid arthritis or gout), muscle diseases, evidence of neurological deficits, and/ or skin diseases.
each patient signed an informed consent form prior to the baseline examination. Estimation of the sample size was based on a pilot study (n=7) that compared the immediatee effect of TTM (four patients) with that of control treatment (three patients) for subjects with back pain associated with MTrPs. Based on data of the pilot study, a starndard deviation (of HF power) of 919.7 was used to calculate the sample size needed to detect a 866.1ms^2 change in HF power (based on the post-test mean differences between groups) which was considered as the level to accept clinical significance of the results with 80% power and 5% significance. In addition, a drop-out rate of 20% was allowed for in estimating the total sample size. According to these criteria, 36 patients were recruited.