The weakest muscle in the human body is the stapedius in the ear. The weak link to hearing modulates the conduction of sound. The muscle is the primary sound-generated reflex in the body.
In terms of the exertion of pressure, the strongest muscle in the human anatomy would be considered the masseter, or the muscle of the jaw. According to the Guinness Book of World Records, the strongest bite ever to be recorded was close to 1,000 pounds. While that claim may sound exaggerated, the jaw does show its strength nonetheless. Bites have been recorded as forceful as 200 pounds.
If one measures strength by the hardest working muscle, the heart would be the top muscle in that category. According to the Wonderopolis website, the soleus, which is located below the muscle in the calf, is the most forceful muscle. Without its aid, people could not walk or run.