What is the function of the muscle in the human body that exerts the most pressure?

If you define strength to mean the ability to exert the most pressure, then the strongest muscle in the human body is the masseter muscle. Of course, you probably call the masseter your jaw muscle.

This thick cheek muscle near the back of your jaw opens and closes your mouth when you chew. How strong is it? The Guinness Book of World Records claims the strongest bite ever recorded was 975 pounds of force! Of course, the jaw doesn't always work with that kind of strength, but it can regularly apply as much as 200 pounds of force on your molars when biting and chewing.