wheelbarrows hurt. I did them with a woman 3 inches taller and about 60 lb. heavier than me and I was in pain when it was my turn to carry her legs. I couldn't figure out how to stabilize my lower back when I was doing them, I don't have a back problem. they seem like they're great for strengthening the back but I couldn't say which muscles in particular. Good luck continuing to prepare for your fight next month.
Sig Credit to Toxic