Earlier quoted context omitted.
"Pacer" is a common word used to describe many activities that are time limited. It takes the common noun "pace" and a average English speaker )or really even a non native speaker) could figure out "pacer" means "to keep pace".
For someone who does not run marathons, I’d ask why a human would be necessary? People could use smartwatches, or there could be waypoint signs. This is a domain specific thing. Without Googling, did you know what a patternmaker is?
You have pacers in most "official" races. Plenty of pacers in 5K's, 10K's, 15Ks, and Halfs. People want to focus on running their time at a constant pace and not having to speed up and slow down every mile.
I assume a patternmaker is someone who focuses on making patterns, probably novel, with sewing and crocheting. I'll google it and edit this post once I confirm it.
Edit: https://www.merriam-webster.com/dictionary/patternmaker
Yep, seems close enough. Amazing what one can do with basic logic.