Author(s): MELVIN, A., AUDET, A., NAAZ, S., KOZLOFF, K., LEPLEY, A., Institution: UNIVERSITY OF MICHIGAN, Country: UNITED STATES, Abstract-ID: 1383

INTRODUCTION:
Habitual physical activity has numerous holistic benefits; however, some research suggests long-term participation in endurance exercise may lead to alterations in autonomic function. Existing research aiming to understand the relationship between endurance exercise exposure and heart rate control have focused primarily on older lifelong runners, elite athletes, and males. Evaluating the connection between cumulative years of regular endurance training (training age; TA) and heart rate (HR) response during and immediately following exercise provides an opportunity to understand autonomic control in a generalizable population of endurance exercisers. The purpose of this study was to determine if TA has an effect on HR response during exercise and recovery in healthy male and female endurance runners.
METHODS:
189 runners (94M, 95F; 35.9±12.1y; VO2max M: 51.9±8.8, F: 46.8±6.9ml/kg/min) training for an upcoming competition performed a graded maximal treadmill cardiopulmonary exercise test. Test protocol was dictated by self-selected half marathon race pace with 1kph increments every 3min until volitional fatigue. Metabolic data were collected breath-by-breath. HR at 10% increments of VO2max were calculated as five-breath moving averages corresponding to the first instance when five consecutive VO2 values met or exceeded the % value. Recovery HRs were recorded every min for 5min post-exercise. Participants self-reported TA and were grouped in 5y increments up to >20y. Pearson correlations assessed the relationships between chronological age (CA) and TA as continuous variables, with HR at each % VO2max and post-exercise HR recovery each min. Repeated measures ANCOVA (TA group x % VO2max stage) with CA as a covariate assessed the overall effect of TA on HR response at each stage during and after exercise.
RESULTS:
CA and TA had significant, moderate negative correlations to HR at each stage (r^2 = -.17 to -.63, p<.001) and HR recovery at each min (r^2 = -.25 to -.49, p<.001). There was no significant interaction effect for TA group by stage (p>.05). A significant effect for stage showed that HR was different at all % VO2max and recovery intervals regardless of group (p<.001). There was a significant effect for group, where those with TA >20y had significantly lower HR than all other groups regardless of stage of exercise or recovery (p<.05), however the effect was insignificant when using CA as a covariate (p=.95).
CONCLUSION:
CA is significantly related to lower HR at comparable workloads throughout an exercise test and recovery, regardless of TA. This suggests that autonomic HR control during and after exercise is driven more by CA than TA in a general healthy population of endurance runners.

This study received funding from Apple Inc. The funding source had no role in the analysis and interpretation of the data or in the submission of this abstract.