CARDIAC DRIFT IS INFLUENCED BY EXERCISE INTENSITY
Murphy, K., Winger, J., & Stavrianeas, S. (2009). The onset and magnitude of cardiovascular drift depend on exercise intensity in competitive cyclists. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 699.
"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." This study examined the potential effects of cardiovascular drift on aerobic and anaerobic metabolism. Competitive cyclists (N = 11) performed five tests on a calibrated cycle ergometer 3-5 days apart: a maximal oxygen consumption (VO2max) test (2-minute stages to exhaustion); a Maximal Lactate Steady State test (MLSS); and three prolonged submaximal bouts (each of 90 minutes duration) at intensities corresponding to 95%, 100%, and 105% of the MLSS intensity (average intensities of 190W, 199W, and 209W respectively). Heart rates and VO2 were recorded continuously during the first two tests, and during the first 35 minutes of the three longer bouts, and every 10 minutes for the remaining duration of the tests. Blood lactate was measured at the end of each stage during the first two tests, and every 10 minutes for the three prolonged bouts.
Only three cyclists were able to complete the 105% MLSS bout, so comparisons were made only for an exercise period of 35 minutes. Onset of cardiovascular drift was different for every S, often with no heart rate plateau in the 105% MLSS bout. Small differences in exercise intensity (<10W) yielded statistically significant differences across the three intensities for the amplitude of cardiovascular drift (average increases of 6 BPM, 8 BPM, and 9 BPM for the 95%, 100%, and 105% respectively), VO2 (no change, 2 ml/kg/minute, and 4 ml/kg/minute respectively), and blood lactate (average increases of 0.3 mmol/l, 0.5 mmol/l, and 0.9 mmol/l respectively) between steady state and minute 30.
Implication. The onset of cardiovascular drift is affected by the intensity of exercise. The amplitude of cardiovascular drift is greater as exercise intensity increases.
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