Here we are, April first and what do I have for you? In honor of April fool's day, this item might seem great at first, unfortunately it also comes with a curse.
Girdle of Overexertion
This item closely resembles a girdle of giant strength and will act as one when the wearer first uses it. Any use of it afterwards will result in a pulled muscle, sprained ankle, or some such problem. They roll a save vs. spells/spell like devices and if they make it, they are only incapacitated for that round. If they fail, then they can't act in combat. They can only move, hunched over, saying something about lifting with the legs next time or something like that, until they can take a rest and maybe get a massage or whatever. Now if they rolled a 1 on their save, well they are down for the day clutching their lower back and mumbling something about their lumbago.
Cure light wounds can be used to get them back to normal for the time being, but the girdle cannot be removed except with a casting of remove curse. This means if they take another action that could result in overexerting themselves, they will have to roll to save again.
I hope someone out there gives this a shot and lets me know how it went. Remove curse is a third level cleric spell in Labyrinth Lord so for a mid level group it should not be crippling. Go ahead and toss into a low level groups treasure cache, hehe. Take care all!