i nanny a 16 month old baby girl. when she is very tired she tenses up her body and does this humping motion. is that normal? ive never seen a baby do that.

Hmm, that is strange. Have you told the parents?

they told me she does it when she is tired... but i just think its so werid. her body gets SOO tense. its hard to mover her arms or legs

That is weird... normally I would say that if the parents aren't worried that it's not a problem... but that doesn't sound good. If she is so tense that it is hard to move her arms or legs and she does that 'humping motion', than she might need to go to a doctor...
Does she do it every time she gets tired or is it just once in a while?
Does she draw her legs up to her stomach?
Are her hands clenched tightly?
Does she appear to be in any pain?

Oh, and that could be an early symptom of autism... ask her parents to hold off any more vaccinations or immunizations until she's older. They can cause autism (several different families we know have had that happen to their children recently).

sounds like convulsions or fits.
what does she do when she is having these?