I thought I was in decent shape. 28y/o, female, 5'10", and 136lbs since I was 18. Then I took up jogging two months ago and realized I couldn't run for more than 30 seconds without gasping for air, as if I'm asthmatic or something.

So I started walking/jogging intermittently for about 30 minutes a day, everyday. It made my knees and feet sore. Eventually cut back to just walking until I could build up to more impactful activity. That took about a month.

Imagine if I had to discover those obstacles in rain or snow, for longer durations, or at higher intensities. If I needed to escape an assailant, I'd have 45-60 seconds to ditch them before I just couldn't keep going.