Heart rate variability (HRV) is a valid and reliable tool that can be used to determine the basic state of an individual\u27s autonomic health. The current study attempted to establish the minimum frequency of breathing practice necessary to produce a therapeutic effect on HRV over the course of a four-week period with four different treatment groups, specifically, groups that practiced a slow breathing protocol for either 2, 3 or 5 times per week, and a control group. Forty-three subjects (14 males, 29 females), ages 18–50 years, were screened, pre-tested, matched for sex, age and HRV, assigned to a specific group for a four-week training period, and completed the study. All pre- and post-test measurements were made during a 10-minute period of supine rest, and included systolic and diastolic blood pressure (BP), heart rate (HR), and the following HRV measures: standard deviation of the normal to normal R waves (SDNN), root mean square of successive differences (RMSSD), high frequency power (HF), low frequency power (LF), and HF/LF ratio. During the 4-week training period, subjects kept a log of their breathing training and then returned for post-testing of the same variables. A two-way analysis of variance with repeated measures on one factor and post hoc T-tests were used to evaluate the data. Significance was set at the 0.05 level. Following the 4-week training period, the control group experienced an increase in systolic BP, while all three training groups experienced a decrease. For diastolic BP, the control group experienced an increase, while only the 2 times per week training group experienced a decrease. For HR, the 2 times per week and 5 times per week groups demonstrated a decrease, while no other groups changed. There were no differences in any HRV measures as a result of training in any group. In conclusion, although previous research had found that breathing training affected HRV measures, there was no effect in this study regardless of the frequency of training. Breathing training did cause a reduction in resting BP and heart rate, but the frequency of training had little to no differential effect. The study was unable to demonstrate a minimum frequency of breathing training for affecting the autonomic nervous system
