HIT (High Intensity Training) workouts such as fast runs, sprints, doing three sets of five burpees in two minutes lead to minor bleeding that shows up as pink sputum. If I persist for several weeks the sputum becomes blood red, and looks pretty scary. My doctor says I was smart to give up HIT workouts.
I first noticed this phenomena about December 2018. I spent 2019 and spring 2020 experimenting with different running programs to see if I could "sneak" around this issue. August 2020, I finally accepted it, shifted my workouts to the range of what is called aerobic heart rate, for me about 110 - 120 beats per minute, and the bleeding issues ended.
