Maximum amount of time for anaerobic exercise

Question

I'm a 29 year old reasonably fit man. I used to run regularly but haven't ran much for the greater part of two years now. I do my 10 minute commute on a road bike daily, usually trying to go as fast as possible. I also practice the relatively niche sport of freediving where I train to hold my breath for a few minutes and swim to depths without air. My heart rate usually drops to 38 to 42 when I'm doing a breath hold (in the air, i.e. without the mammalian dive reflex).

I picked up running again just yesterday (for a race which is in ten days), and I was surprised to see that my HR monitor reports I'm doing most of my run in anaerobic, cf. the screenshot below.

Is there a maximum amount of time one should spend doing anaerobic exercise before it gets eventually dangerous? What should I watch out for if most of my running is in this HR range?

Answer 1

Your machine is incorrect.

Anaerobic literally means "without oxygen". It is impossible for you to be spending 19 minutes of a 25 minute workout without oxygen. Anaerobic lasts anywhere from 10-30 seconds normally.

I would suspect that somewhere in the algorithm where it compares resting and "max" heart rate it thinks that because of an elevated measurement for heart rate, it arbitrarily decides that you are in an anaerobic state, which isn't actually the case.