A "pace" is a speed that you choose for yourself. When you're running, swimming, bicycling, etc. you choose a "pace" that's fast, but not so fast that you'll get tired out and not able to continue. To "keep up" a pace means to continue going at the same speed:
If she can keep up that pace, she might even break the world record.
You can also use "pace" and "keep up the pace" to talk about work. When you're busy at work, you can say:
I've got so much going on right now. I don't know how I'm going to keep up this pace.