The Onset And Magnitude Of Cardiovascular Drift Depend On Exercise Intensity In Recreational Runners

Abstract

Cardiovascular drift (CVD) is a gradual increase in heart rate (HR) during prolonged steady-state exercise. Despite considerable research on the etiology of this complex phenomenon, little is known as to the effects of CVD on energy consumption. PURPOSE: To examine the potential effects of CVD on aerobic and anaerobic metabolism. METHOD: Recreational runners (n=10, age 40.3±8.3 years, height 176±7 cm, weight 71.29±10.76 kg, VO2max 57.29±5.96 ml·kg-1·min-1) volunteered for this study and signed informed consent forms. Each participant performed 5 running tests 2-4 days apart: a maximal oxygen consumption (VO2max) test (2-min stages to exhaustion), a Maximal Lactate Steady State test (MLSS), and 3 prolonged submaximal bouts (45 min duration each) at intensities corresponding to 95%, 100%, and 105% of the MLSS velocity (1% grade). HR and VO2 were recorded continuously throughout all tests; blood lactate was measured at the end of each stage during the first 2 tests, and every 10 minutes for the 3 prolonged bouts. All protocols were approved by the IRB. RESULTS: Only 3 runners were able to complete the 105% MLSS bout. Onset of CVD was different for every participant, often with no HR plateau in the 105% MLSS bout. Small differences in exercise intensity (0.22 m·sec-1) yielded statistically significant (p < 0.05) differences across the three intensities in the amplitude of CVD (increases of 7 BPM, 14 BPM, and 18 BPM for the 95%, 100%, and 105% respectively), VO2 (1.42 ml·kg-1·min-1, 1.8 ml·kg-1·min-1, and 1.39 ml·kg-1·min-1 respectively), and blood lactate (0.25 mmol·L-1, 0.88 mmol·L-1, and 1.08 mmol·L-1 respectively) between steady state and minute 40. CONCLUSION: We successfully measured the small changes associated with the metabolic cost of exercise during CVD. Our data conclusively indicate that the onset of CVD is affected by the intensity of exercise and the amplitude of CVD is greater as exercise intensity increases. Supported by the Mary Stuart Rogers Foundation and an NSF grant (DUE 0511219).