Which preposition to use with overtaxing

at Occurrences 1%

Still there was a delay of some months, which was partly due to the nurses' need of further training, and partly to the imperative necessity that she should have entire rest in order to recruit the strength which had been so sorely overtaxed at the Great Northern Hospital.

on Occurrences 1%

She did not want her strength to be overtaxed on her first day out of bed.

Which preposition to use with  overtaxing