As you bite into a crisp apple, your jaw muscle contracts, allowing you to grind the fruit between your teeth. When you climb a flight of stairs, your gluteus maximus (or "glutes") push your body upward against gravity. Meanwhile, your heart beats steadily in the background, pumping blood continuously.
Each of these muscles, and all the other muscles in the human body, plays an important role. But what is the strongest muscle in the human body?
That question doesn't have a single answer. It depends on how you define "strength," Sarah Gilliland, a clinical professor in the Department of Rehabilitation Sciences at Tufts University School of Medicine, told Live Science in an email.
"The answer to this really varies based on whether one is looking at overall torque (or force production) or force production per mass/volume of the muscle," she said. A large muscle might be considered the strongest if total force output is the measure, but a smaller muscle could take the prize if strength is judged relative to its size and efficiency, Gilliland explained.
Dominic D'Agostino, an associate professor and physiologist at the University of South Florida Morsani College of Medicine, agreed that the definition of muscle strength varies.
"Scientists typically define muscle strength as the maximum force a muscle or muscle group can produce," he told Live Science in an email. In practice, this can be measured by the heaviest weight a person can lift once, or by the peak force or torque recorded on a dynamometer in a lab. But sometimes, scientists also look at endurance strength, or how well a muscle resists fatigue during prolonged activity.
Sign up for our weekly Life's Little Mysteries newsletter to get the latest mysteries before they appear online.
When it comes to absolute force, the gluteus maximus — the muscle of the buttocks that straightens the leg at the hip — tops the list.
"The gluteus maximus is the largest muscle in the body (by mass) and it primarily acts to straighten the hip," Gilliland said. It creates enough torque to lift the entire body and powers everyday movements like standing from a chair, climbing stairs and running. "Its large size and high density of fast-twitch fibers contribute to its major force output," D'Agostino said.
The quadriceps, a group of four muscles on the front of the thigh that straighten the knee, are also in the running for strongest when you consider torque production, Gilliland said. However, because they function as a group, it's difficult to isolate their strength, she pointed out. The soleus, a calf muscle, is another contender for the highest force production, D'Agostino said.
"The quadriceps and soleus muscles collectively enable lifting your entire body weight (or more) during movements like standing, running or jumping," D'Agostino said, making them some of the highest force producers in the body.
But the strongest muscle by weight is the masseter, a chewing muscle in the jaw, D'Agostino said. It is small, but it has many fibers packed into it and has a perfect 90-degree insertion angle on the jaw. These factors allow it to produce incredibly large amounts of torque for its size, Gilliland explained.
Endurance is another way to think about strength. From the perspective of resisting fatigue and doing lifelong work, the heart — which contracts continuously, about 100,000 times per day, pumping roughly 2,500 gallons (9,500 liters) of blood daily — has superior endurance strength, D'Agostino said.
The tongue is also tireless; it mixes food, shapes speech and pushes saliva down the throat even during sleep. The eye muscles, too, are in constant motion, making up to 10,000 coordinated movements in just an hour of reading.
"Different muscles excel in different aspects of strength," D'Agostino said. So the strongest muscle in the human body depends on the job at hand.
Editor's note: This mystery was originally published on Sept. 29, 2010 and rewritten on Oct. 10, 2025.
