Heart rate and exercise intensity during training: observations from the DREW Study

OBJECTIVE: Cardiovascular drift (CVdrift) is characterised by a continuous, gradual increase in heart rate (HR) after approximately 10 min of moderate-intensity aerobic exercise, despite maintenance of a constant work rate. This has important implications for trials that employ HR to monitor exercise intensity, as reducing work rate in order to keep HR constant could result in participants exercising below the intended intensity. Utilising the Dose Response to Exercise in Women (DREW) database, we sought to determine if increases in HR during exercise (CVdrift) resulted in clinically significant reductions in exercise work rate in order to keep HR within a target range. DESIGN: Randomised, prospective study. SETTING: DREW clinical exercise trail, The Cooper Institute, Dallas, Texas. PARTICIPANTS: Overweight (body mass index 25-43 kg/m2), previously sedentary postmenopausal women (n=326). INTERVENTION: Treadmill and cycling exercise (30-90 min, three to five times per week) at a HR corresponding to 50% of peak oxygen uptake (VO2peak). MAIN OUTCOME MEASURE: Changes in exercise intensity (metabolic equivalents (METS)) during exercise in response to CVdrift. RESULTS: We observed small increases in HR (1-4 beats per minute, p<0.001) combined with small increases in intensity (0.01-0.03 METS, p<0.03) during the combined 12 963 exercise training sessions. Further, we identified only 101 (0.78%) sessions in which intensity was reduced during the course of the exercise session, potentially in response to CVdrift. CONCLUSIONS: We conclude that CVdrift did not contribute to significant reductions in exercise intensity in the DREW study.