Longitudinal Effects of Voluntary Aerobic Exercise on Heart Rate and Rhythm, their Autonomic Modulation, and Body Weight and Frailty in Older Rats
Authors: Rutishauser Carolyn Ann , Bonin Janet Elise , Axsom Jessie , Lakatta Edward G. 
Published: June 2021

PurposeIt has been well documented that aging is associated with a reduced heart rate (HR) and heart rate variability (HRV), a reduction in body weight (BW), and increased risk of frailty. The impact of chronic voluntary exercise coupled with aging on these parameters in older rats is unknown. We determined the effects of voluntary aerobic exercise on BW, HR, HRV and their relation to autonomic input, and frailty index (FI) in a longitudinal aging rat model.MethodsBaseline and repeated measures of experimental variables were recorded in 40 male F344 x Brown Norway rats on entry (EAge) into the study (between 15 and 25 months of age) and over time following EAge until death (on average 31 months). Individually housed rats at each of 3 EAges were randomized into two groups: 1) “Voluntary Wheel Exercise” (VWE) group had access to a running wheel, and 2) a control group that did not have access to a wheel. Body weight (BW) for both groups was recorded once per week. ECGs were recorded monthly via telemetry devices in awake, unrestrained rats. A 1.5‐hour basal recording was followed by a double autonomic blockade (0.55 mg/kg Atropine and 1.1 mg/kg Propranolol administered intraperitoneally) to obtain the intrinsic heart rate (IHR). ECGs were analyzed with Labchart, and statistical analysis of HR and HRV was performed in R and Python. FI scores [adapted from the Rat Clinical Frailty Index] were recorded at baseline and repeated 2 to 4 times throughout lifespan.ResultsThe mean heartbeat‐to‐heartbeat interval (mean NN in table) and numerous HRV parameters in the basal and intrinsic states were decreased at increasing EAge and the change over time following EAge increased as EAge increased (EAge: Time in table). VWE affected the mean intrinsic NN and numerous HRV parameters in the basal and intrinsic state (VWE in table). The effect of VWE on EAge (VWE: EAge in table) for mean intrinsic NN and several basal and intrinsic HRV parameters was also dependent on EAge, and the effect of VWE on intrinsic NN and a few HRV parameters changed over time following EAge (VWE: Time in table). A similar relationship between entry age and duration of exercise is observed with BW. Frailty index decreased with aging but was not affected by VWE.ConclusionsOur study confirms that aging alters overall heartbeat‐to‐heartbeat variability and that the voluntary wheel exercise has a marked impact on these variables. A greater exercise effect was observed in the intrinsic HR and several frequency and non‐linear domain parameters. Observed EAge: VWE interaction term suggests that age at which exercise is initiated influences its long‐term effects. Additionally, exercise duration time‐effect in a model of chronic voluntary exercise influences its effect on IHR.Support or Funding InformationFunding Information: Funded by the National Institutes of Health/National Institute on Aging Intramural Research ProgramThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.