Support runner fitness

What type of support running are you going to be doing?  Ultra Trail Run, Guide for disabled, other?

If you are a pacer for an Ultra Marathon you may be running 10-30 miles while the registered athlete is running 100+ miles.  No, you don't have to be in as good of shape as the guy doing 100+ miles if you are only doing 10 miles, but know that for those 10 miles (or 20 or 30) that you will be working harder than the registered runner.  In addition to running 10 miles at the pace of the registered runner.  You will be the one making sure that your runner doesn't miss turns, stays on track with a nutrition & hydration plan, stays motivated, stays on pace, etc.  

I was thinking of the pacers for Eliud Kipchoge when I replied but didn't use that example because I thought it might be confusing.  When you are the fastest guy in the world you can't find someone that is more fit than you to be your support runner.  Those guys were not as fit as Eliud but they got to rotate out so they were able to do their job.  They were working harder than Eliud for the segments that they ran.  They had to do the same pace as Eliud while they were on the course but they did not have anyone to block the wind for them like they were doing for Eliud and they has to pay attention to where they would be trading out so that the transition was smooth, etc.  Those guys at least had a truck in front of them setting the pace and plotting the race route so they didn't have to navigate and set the pace on top of everything else they were doing.  They were all really fit guys though and I am guessing they all were sub 2:30 marathoners.