The Effects of Stretching Training on Cardiac Autonomic Function in Obese Postmenopausal Women

Context • Menopause and obesity are associated with autonomic dysfunction. Unconventional exercise modalities that include an important flexibility component seem to improve cardiac autonomic function by lowering sympathetic tone and increasing vagal modulation of the heart rate (HR). Yet clear evidence of the effects of stretching training (ST) on cardiac autonomic modulation is limited. Objective • The present study intended to examine the effects of ST on HR variability (HRV) and flexibility in obese postmenopausal women. Design • The research team designed a randomized, controlled trial. Setting • The study was conducted at the Florida State University (Tallahassee, FL, USA). Participants • Twenty-four obese, postmenopausal women, aged 50-65 y with a body mass index of >30 but <40 kg/m2 participated in the study. Intervention • Participants were randomly assigned either to an ST group (n = 12) or a no-exercise control group (n = 12). The study was 8 wk in duration. Outcome Measures • Participant HRV and sit-and-reach scores (SRSs) were measured at baseline and after 8 wk of training. Results • Significant decreases occurred for the ST group between baseline and postintervention in sympathetic activity, as measured by normalized low frequency (nLF) power, and in sympathovagal balance, as measured by the ratio of the natural logarithm low frequency (LnLF) activity to the natural logarithm high frequency (LnHF) power, with P < .01 for both measures. The decreases for the ST group were significantly greater than those for the control group for the nLF and LnLF/LnHF, with P < .05 for both measures. Significant increases in vagal tone occurred for the ST group between baseline and postintervention, as measured by the normalized high frequency (nHF) power, with P < .01, and in SRS following ST, with P < .001. The increases for the ST group were significantly greater than those for the control group for the nHF and SRS, with P < .05 for both measures. The changes in SRS were correlated with the changes in the LnLF/LnHF power, with r = .65 and P < .03 negatively correlated. Conclusions • The findings indicated that ST can improve cardiac autonomic modulation by increasing vagal tone and decreasing sympathetic activity in obese postmenopausal women. The improvement in SRS partially explained the decrease in the sympathovagal balance. Because older or obese individuals have a higher risk of developing cardiovascular diseases, they could potentially benefit from ST.