I had abdominal pains last week when ever I was out bocking.
Its pretty much gone now and my Doctor said it was just muscules being used that I wouldnt have normally.
Though it wasnt due to a funny landing, it was becasue I was trying to jump higher and to do so, I needed to use more muscules in my body
Take some time off your bocks, I took 2 days off, got back on them, it hurt... so I took 2 more days off.
Loads of people have different parts of their body being effected, though most of the time, a sore back is due to "bockers back".
Just take it easy on your stilts once your back on top of things, dont push yourself... there is no race, just enjoy it al