When I first started running outside, I had no idea on pace. I ran at what I felt was "reasonable" and what I felt was similar to my experience of treadmill ru

When I first started running outside, I had no idea on pace. I ran at what I felt was "reasonable" and what I felt was similar to my experience of treadmill runs. It was really rough and hard work! Tl;Dr - I got a basic thing that told me my pace (this was pre-smartphones but basic wearables existed) and turned out what I thought was relatively gentle and reasonable speed was actually a really fast pace and totally unsustainable. When I knew what my pace actually was, I could stick to a much more sustainable (for me) ~5:30 min/km pace and it felt soooo slow and embarrassing and like I was barely even moving in comparison! But this was a much more realistic pace for a tubby software engineer. And for a long time I had to keep checking the pace as the speed would creep up during a run and it took discipline to "stay slow". I use the runkeeper app that has the option to do pace read outs through your headphones every few minutes. I'd recommend trying something like that, and perhaps try to begin with a pace of like 6 or 7 min/km for 10-15 mins runs and stick to it and see if that helps, before starting to extend duration and speed after you've built some endurance. I've found fitness and condition improves fairly rapidly - O(weeks). Good luck.