A junk mile is a run done at a moderate intensity, typically 70–85% of your max heart rate. The gray zone—where junk miles live—is neither easy enough to promote recovery nor hard enough to drive meaningful adaptation. Spending too much time here can lead to stagnation, increased fatigue, and a higher risk of injury.
How to identify junk miles?
Test 1: The Heart Rate Test
If you wear a monitor, check your average heart rate during the run.
- True easy running sits at 60 to 70% of max HR, around 120 to 140 bpm depending on fitness and age.
- True hard running sits at 85 to 95% max HR, around 160 to 180 bpm.
If your easy runs are landing at 75 to 82% max HR, you’re in the moderate zone.
If your workouts aren’t designed around a specific pace or threshold target, they’re probably moderate-intensity junk.
Test 2: The Talk Test
- During the easy run, you should be able to speak in full sentences.
- At hard pace, you should be able to speak only a few words at a time before gasping.
If your easy runs require conscious effort or feel more like a workout than relaxed movement, you’re running at a moderate intensity and not getting the recovery benefits you need.
If you’re at a pace where you can speak but feel like you need to take breaths between phrases, you’re in the moderate zone.