Does Sitting Position Matter in Heart Rate Variability Biofeedback?

This randomized controlled study examined whether sitting position affects HRV frequency domain and time domain measures. Forty-one undergraduates (20 male and 21 female), 19-24 years of age, participated in this study. A Thought Technology ProCompTM Infiniti system monitored abdominal SEMG, ECG, HRV, and respiration. The SEMG active electrodes were placed 1-1/2 inches below the navel and 2 inches to either side. The reference electrode was equidistant from each active. ECG active electrodes were placed about 2 inches above the navel and 4 inches to the left and right of the midline and the reference electrode was centered over the angle of the sternum. A respirometer was positioned over the navel to measure abdominal excursion and respiration rate. Subjects were stabilized for 5 min and then were observed with eyes open and no feedback in each of the three sitting positions for 5 min with a 2-minute buffer period between conditions. These positions were leaning forward (45[degrees]), sitting upright (90[degrees]), and leaning backward (120[degrees]). Data were analyzed using a GLM analysis with familywise correction. Sitting position did not affect abdominal SEMG, abdominal excursion (the difference between maximum expansion and contraction), or respiration rate. However, an upright sitting position produced greater low frequency power (LF n.u.) than leaning forward, F(1, 22) = 15.56, p = .001, [[eta].sup.2] = 0.41, and leaning backward, F(1, 22) = 7.94, p = .01, [[eta].sup.2] = 0.27. Consistent with this finding, an upright position produced lower high frequency power (HF n.u.) than leaning forward, F(1, 22) = 15.56, p = .001, [[eta].sup.2] = 0.41, and leaning backward, F(1, 22) = 7.94, p = .01, [[eta].sup.2] = 0.27. These outcomes were not mediated by respiration rate, which did not vary across sitting positions. Sitting position did not affect any of the major time domain measures of heart rate variability (HR Max-HR Min, NN50, pNN50, RMSSD, SDNN). Since increasing LF power is a major goal of HRV biofeedback, we recommend training in an upright sitting position for subjects who resemble our undergraduates. Future researchers should replicate these findings with clinical populations. Keywords * Heart rate variability biofeedback * Sitting position