There is not a single muscle in the human body that is the strongest. The gluteus maximus is the largest muscle and is powerful enough to keep the body erect. The heart is the hardest working muscle, pumping at least 2,500 gallons of blood daily.
The muscle with the greatest force is the masseter muscle in the jaw, which exerts a force as great as 55 pounds when closing the jaw on the incisors and 200 pounds on the molars. The soleus muscle found below the calf muscle has the greatest pulling force of all the muscles. The soleus, along with the calf muscles, must pull against gravitational force to hold the body upright.