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The Importance Of Understanding Cardiac Drift
If you use heart rate to measure your effort, especially during easy and long runs, you need to understand what effect cardiac drift has on your heart-rate readings or you’ll constantly be under-performing in workouts.
Let’s assume you’re targeting a marathon-paced run within your aerobic threshold training zone (80-85 percent of your maximum heart rate). For ease of math, let’s assume your maximum heart rate is 200 beats per minute, which puts your aerobic threshold training zone range at 160-170 beats per minute.
For the first 20-30 minutes of your run, a pace of 8 minutes per mile might put you within that goal range, which will probably also be your goal marathon pace.
After 30 minutes of running, cardiac drift may cause your heart rate to increase so that you have to slow down to maintain that heart-rate window of 160-170 bpm. However, this decrease in pace does not correspond to your effort or fatigue levels.
Now, you’re running at 8:15 per mile pace and spending less time training at your marathon potential and thereby not getting the most out of your workouts or your training time.
Calculating Calories To Lose Weight
Another potential issue to be aware of in regard to cardiac drift is the calculation of calories burned during a run. Many online calculators and fitness machines use heart rate to measure effort and thereby calculate calorie expenditure.
As we’ve learned by looking at cardiac drift, an increase in heart rate doesn’t necessarily correlate with an increase in effort, oxygen uptake, or calorie expenditure. So, using your heart rate as a way to measure calories burned, which is a built-in feature on many heart-rate monitors, could lead to false data and eating too much if you’re trying to lose weight.