There`s a sarcastic smart-alecky little phrase we often use in the U.S., it`s:
"Don`t strain yourself!"
You`d use this on someone who won`t do his/her share of their work, and are generally dragging butt.
If you`re driving your car up a steep incline, your car`s engine will be under stress, therefore it (the engine) will be straining to pull the car forward.
The words are related, but not completely interchangeable.
This is a tough one, I wish I could help you out more. Did you try looking up the words in a dictionary?
P.S.- I have a question for you. Why is the hampster eating your finger?