Post-exercise Hypotension after Resistance Exercise and Diminished Sympathetic Vascular Responsiveness in Older Women

Abstract

1348 The general view is that post-exercise hypotension (PEH) arises from a reduction in systemic vascular resistance. However, no hemodynamic data are available to support this hypothesis following resistance exercise (RE) in older women. PURPOSE: This study examined hemodynamic responses during and for 1-hour after two knee extension RE conditions (15-RM and 5-RM) in 16 young (mean age = 21 ± 2.3 yrs) and 16 older (mean age = 69 ± 2.3 yrs) women. METHODS: Hypotension was measure as the magnitude of blood pressure (BP) drop below baseline following single bouts of 5-RM and 15-RM RE. Continuous BP and ECG data were acquired at 200Hz, converted to tachograms, re-sampled at 4Hz, and smoothed using a low-pass digital filter with a cutoff frequency of 0.05 Hz. Heart rate and BP data are reported at rest, peak exercise, and throughout 1-hour of recovery. Heart rate variability data were derived from 5-minute segments at rest and after both RE conditions. Forearm vascular resistance (FVR) was derived using mercury strain gauge plethysmography, and reported at rest and every 3 to 5 minutes during recovery. ANOVA with repeated measures was used to examine the effects of test period, age, and exercise condition. RESULTS: ANOVA revealed a significant effect of test condition on BP that was modified by a test condition by age interaction. Older adults had a greater magnitude of PEH in systolic, diastolic and mean arterial pressure (MAP) following RE in comparison to the young group (e.g., max MAP PEH = −2.4 ± 2.0; −9.7 ± 1.5 mm Hg in young and older women, respectively). FVR following RE was also subject to a test condition by age interaction (p = 0.03), increasing above baseline in the young adults at all time periods in recovery, but changing little in older adults. The natural log of normalized low-frequency heart rate variability (lnLFnu) was subject to a main effect of test condition (p = 0.001), but did not differ between age groups. Pearson correlation revealed that lnLFnu was related to recovery of MAP (r = 0.66 and 0.79; p<0.001 in young and older women, respectively) and FVR (r = 0.93 and 0.95; p<0.001 in young and older women, respectively); however, the beta value was higher among young (MAP beta = 0.95, FVR beta = 13.1) in comparison to older women (MAP beta = 0.51, FVR beta = 9.8). CONCLUSIONS: Age group differences in PEH after RE, characterized by a greater drop in BP in older adults, may be attributed to smaller increases in vascular resistance. The similar behavior of lnLFnu across age groups, paired with age-related differences in the LFnu vs. MAP and FVR slopes is consistent with older adults having stiffer and less reactive blood vessels, possibly contributing to a greater magnitude of PEH in older women.