<human>: Can you succinctly summarize the text in 1-3 sentences?

Hi r/running! As of four months or so, I've picked up running again from about 2 years earlier when I ran regular 5k's. I do one hour of spinning and two runs of about 5k per week. I noticed that whilst spinning I felt very out of breath and I was absolutely knackered after training (good). As for running though: relatively easy, nothing too uncomfortable breathwise. I know I am running slower than 2 years ago (8,5km/h now vs 9,5-10km/h) but that is good because it's easier to keep running as I naturally dislike it; running too fast will get me in the "I really don't wanna do this" mode. I'm planning on running a 10k so I'm building up.

I was curious to the difference in heartrate between spinning (I'm gonna die) and running (I'm relatively okay) so I borrowed a heart rate monitor that goes around your chest.
Lo and behold my surprise when on an average run my heartrate went way above 180 (more like 183-187). For my age (F, 31) and weight (136 lbs, 5" 7) that is pretty high. However, I wasn't out of breath at all and I didn't feel exhausted or winded. Heartrate also dropped quite fast after I stopped running.
Spinning is different, relatively lower heartrates (high 170ies) in high intensity intervals, but that felt much more like working out.

So, is this a matter of being in not such a good shape, do I have a natural high heart rate? And, should I train differently? I've read that one could run slower but I feel like already I am going way slower than what is possible and what I've done 2 years ago.
<bot>: I spin and I run. Thought from breath rate that spinning would send heart rates soaring: nope. Running gets my ticker all sorts of crazy without me being very out of breath. Why this imbalance?