Cardiovascular drift

Cardiovascular drift (CVD, CV_drift) is the phenomenon where some cardiovascular responses begin a time-dependent change, or "drift", after around 5–10 minutes of exercise in a warm or neutral environment without an increase in workload.¹² It is characterized by a progressive increase in heart rate accompanied by a decrease in stroke volume, while cardiac output is generally maintained through compensatory increases in heart rate.¹² Depending on environmental conditions, exercise intensity, and hydration status, mean arterial pressure may remain relatively stable or decrease slightly during prolonged exercise.¹² Reductions in stroke volume are largely attributable to increases in internal core temperature and reductions in central blood volume associated with dehydration and the accompanying cutaneous vasodilation.¹² To facilitate heat dissipation, blood flow to the skin increases during prolonged exercise, promoting a redistribution of blood volume toward the cutaneous circulation and contributing to reductions in central venous return and stroke volume.¹² The resulting reduction in stroke volume is largely compensated by a progressive increase in heart rate, thereby maintaining cardiac output over a wide range of exercise intensities.¹² In warm environments, cardiovascular drift is associated with a reduction in maximal oxygen uptake measured immediately after the prolonged exercise bout,³⁴ an effect that can be attenuated by adequate body cooling⁴ or by adapting exercise intensity.³

Cardiovascular drift also has important implications for exercise prescription and monitoring.⁵⁶⁷ During constant-speed or constant-power exercise, the progressive increase in heart rate causes exercise intensity expressed as heart rate to drift upward over time. Conversely, when exercise intensity is prescribed by maintaining a constant heart rate (heart rate-clamped exercise), external workload (such as running speed or cycling power output) must be progressively reduced to compensate for the cardiovascular drift. Experimental studies have shown that heart rate-clamped exercise therefore produces lower external workload and oxygen uptake than constant-speed or constant-power exercise performed at the same initial physiological intensity.⁵⁶⁷ Recent randomized evidence suggests that these acute differences may also influence long-term training adaptations.⁷ In previously inactive adults, endurance training prescribed using constant running speed produced greater improvements in peak running speed and maximal oxygen uptake than training prescribed using a constant heart-rate target, despite identical initial exercise intensity prescriptions.⁷