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HR and Anaerobic Intervals


What is a safe heart rate for the work phase of anaerobic intervals? Can a person safely exceed the calculated 85 percent HRR in a 30 to 45 second interval? I have been encouraging my clients to include intervals in their cardio, but I want to be able to give guidelines for safe exercise. I would appreciate your help with this matter.


This question needs several steps to answer, but if you keep reading, you'll find the complete answer. Step 1 is an explanation with a definition, so here we go.

“Anaerobic intervals” is an expression that is out of vogue with scientists but still popular with trainers. Within the academic field, the term anaerobic has been discontinued unless you are speaking on the cellular level. Cellular respiration when there is inadequate oxygen is an anaerobic state. So terms like anaerobic threshold are not used and have been replaced with non-oxidative intensity or non-aerobic. The current term that is used is HIT (high intensity intervals).

Step 2 of this explanation is the near abandonment of the use of heart rate reserve (HRR) because it is based on a formula that is based on no scientific evidence of 220-age. The age adjusted maximum heart rate formula is useless. Few individuals have taken a sub-max test to estimate their maximum heart rate or a true tested maximum heart rate, which requires the subject to go to the point of exhaustion. Therefore, using a percentage, you suggested 85 percent of a formula that uses a formula that is useless is itself relatively useless.

Step 3 is the encouraging high intensity interval training that is positive for the healthy and fit population. In fact, one can train less time doing HIT training and get as much if not more benefit than steady state or low intensity training. And the final Step 4 is directly pointed to your question, what are safe exercise guidelines for aerobic and non-aerobic training.

After 30 years of teaching cardiovascular training using the training zones, I have to say that if you want "safe," then you need to keep your clients at or below threshold. For clarity, threshold heart rate is that intensity level at lactate threshold, ventilatory threshold or anaerobic threshold. The difference between these three thresholds is minimal, so using the global term “threshold” explains the phenomenon of a physiological marker point where there is a shift in metabolic and breathing response to exercise intensity.

The key is to keep your client training with intervals, recovery, steady state and combination workouts using a heart rate monitor, staying in the zones and burning tons of calories.


  1. Kemi, O. J., Haram, P. M., Loennechen, J. P., Osnes, J. B., Skomedal, T., Wisløff, U., and Ellingsen, O., “Moderate vs. high exercise intensity: differential effects on aerobic fitness, cardiomyocyte contractility, and endothelial function,” Cardiovascular Research 67 no. 1 (2005): 161-172.