Cardiac Drift

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Definition: Cardiac Drift is the tendency for heart rate to rise gradually throughout a workout due to dehydration and rising temperature within the muscles. (Definition provided by Dave McGovern)

Synonyms:

  • Cardiovascular Drift
  • CVD
  • CVDrift

How Cardiac Drift Affects Your Workout

Increased heart rate is seen after 10 minutes of moderately-intense exercise, such as brisk walking or jogging. Heart rate may increase as much as 10 to 20 beats per minute while maintaining the same pace and perceived effort.

This can put you into a higher heart rate zone than you were in at the beginning of your workout at the same effort.

This heart rate increase happens with decreased stroke volume - the heart is pushing out less blood with each contraction. It is beating faster but moving less blood with each beat. The net result is the same amount of blood and oxygen is being sent out to your muscles, but with a higher heart rate.

A faster heart rate with cardiac drift doesn't mean your muscles are working harder, taking in more oxygen or burning more calories. Even as the heart rate goes up during cardiac drift, you aren't breathing faster.

You may have noticed this effect yourself. Your heart rate increases over the course of a walking or jogging workout, even though you may be maintaining a steady pace and you don't feel like you have been expending more effort. If you wear a heart rate monitor and compare pace with heart rate, you may see the rise in heart rate after 10 to 20 minutes although you have not increased your pace.

If you are trying to stay within a set heart rate zone, the higher heart rate seen with cardiac drift may lead you to slow down to get back to your target zone, when in fact you are not working out harder.

Instead of relying completely on a heart rate monitor during a longer workout, trust your own perceived exertion rate and breathing rate to gauge whether you are working out in the right zone.

Maintain your pace knowing that you are getting a heart rate boost that doesn't mean you are putting in more effort.

Fitness monitors that base calories burned on your heart rate will give a false report of more calories burned due to cardiac drift. This can be one reason that the calories burned numbers are different between different fitness monitors.

Causes of Cardiac Drift

It was long thought that cardiac drift was due to increased blood flow to the skin during exercise. However, research reviews say there is little evidence that this is the cause of the increased heart rate. In conditions of heat vs. cold, with a four-fold difference in blood flow to the skin, the stroke volume remained the same. Instead, some researchers think it is due to dehydration and rise in body temperature (hyperthermia) with prolonged exercise.

Cardiac drift is also seen during heat stress and dehydration. Exercising in hot conditions can often produce a much higher heart rate than a person usually experiences with the same pace and duration.

Bottom Line on Cardiac Drift

Cardiac drift is the result of the heart working harder to maintain cardiac output during endurance exercise. If you are aiming for peak performance and efficiency, you need to be aware that your body isn't as efficient as your workouts get longer and longer.

Start any endurance workout well-hydrated and drink enough throughout exercise to prevent dehydration.

Sources:

Wingo JE, Ganio MS, Cureton KJ. "Cardiovascular drift during heat stress: implications for exercise prescription." Exercise and Sport Sciences Review 2012 Apr;40(2):88-94. doi: 10.1097/JES.0b013e31824c43af.

Coyle EF, González-Alonso J. "Cardiovascular drift during prolonged exercise: new perspectives." Exercise and Sport Sciences Review. 2001 Apr;29(2):88-92. (Review)

Coyle EF. "Cardiovascular drift during prolonged exercise and the effects of dehydration." International Journal of Sports Medicine. 1998 Jun;19 Suppl 2:S121-4. (Review)

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