Consider the feedback loop that cools the body when it is too warm

The feedback loop that cools the body when it is warm is a negative feedback loop.
When the hypothalamus sense that the body temperature is too high, it will sends a signal to the skin which will constrict in response thus reducing heat loss. As a result of this muscles will begin to shiver and generate heat, this will increase the body temperature and the signal from the hypothalamus will be reduced.
The stimulus that initiated this process is the hypothalamus while the response is the constriction of the skin and the shivering of the muscles.

They became more resistant.