There are 650 skeletal muscles in the body, and all perform different functions. Some muscles are bigger than others and have more power; others work harder and have greater capacity for consistent work; others can exert tremendous forces.
Gluteus Maximus
The gluteus maximus muscles (buttocks) is the single biggest muscle in the human body. It's the key muscle for keeping the torso erect. Those who don't have enough strength in the gluteus maximus have a difficult time holding up their upper body. Someone who slumps forward or lists to one side or the other likely has weakness in the gluteus maximus muscle.
Heart
The heart is the hardest-working muscle in the body, pumping as much as 2 oz. of blood with every heartbeat.The heart pumps over 2,000 gallons of blood every day and has the capacity to beat nearly 2 billion times in the course of a lifetime. An unhealthy heart loses its capacity to pump the maximum amount of blood, and the result is usually fatigue. Severe heart disease stops the heart from pumping and results in death.
Masseter
The masseter is the strongest muscle in the body based on its size. The masseter, in the jaw, controls the amount of force that's exerted during chewing and eating. The masseter can close the muscles of the jaw with a force as great as 55 lbs. overall and 200 lbs. for just the incisors. No other muscle can provide this amount of brute force.
