Skeletal muscle attaches to joints and long bones and is under the control of the conscious brain. As you read this blog, occasionally typing on your keyboard, it’s skeletal muscle directing your fingers through their finely-tuned tap dance.
(FYI: Aside from skeletal, there are two other major muscle types in your body: smooth and cardiac. Smooth is involuntary and non-striated. Generally, it’s either fully contracted or fully relaxed. Your urinary bladder, lungs and the irises of your eyes are controlled by smooth muscle. Cardiac muscle is also involuntary – doing its job automatically – but striated, meaning parts of it are able to contract while other parts do not. Your heart is composed of cardiac muscle.)
In this confocal fluorescent light micrograph by Thomas Deerinck at the National Center for Microscopy and Imaging Research at UC San Diego, you’re looking at a cross-section of parallel skeletal muscle fibers (stained red due to the presence of the proteins actin and myosin) sheathed in a sugar-protein complex (green). Cell nuclei are stained blue.
There are roughly 700 muscles in the body, in all shapes and sizes. The biggest single muscle is the Gluteus maximus, one of three muscles that comprise each buttock. Our big butts help make it possible for us to stand, move upright and run. Indeed, a 2006 paper by Harvard and University of Utah researchers suggested giant glutes make humans the undisputed best long-distance runners in the history of life on Earth.
The widest skeletal muscle in the human body is the Lastissimus dorsi, which is Latin for “wide back.” It’s the muscle that begins at the spine, fans out and attaches at the other end to the upper arms.
The longest muscle is the Sartorius, which begins at the outside of the hip, runs down the upper leg and terminates inside the knee. The name Sartorius means “tailor,” so-called because this muscle allows one to cross one’s legs, purportedly a common position assumed by working tailors. The Sartorius also assists in flexing the knees and hips.
The Gluteus maximus often is dubbed the strongest muscle because it works to keep the entire body upright, but there are many ways to measure strength:
The muscles of the uterus, for example, must be strong enough to push a baby through the birth canal.
The heart beats continuously for as long as you live – more than 3 billion times in a person’s life, pumping approximately 2,500 gallons of blood every day.
Similarly, the muscles of the eyes are constantly repositioning them. In an hour of reading, the external muscles of the eyes will make nearly 10,000 coordinated movements.
And let’s say something for the tongue, which is a bundle of tireless muscles. While eating, it moves around mixing food to aid digestion. It binds and contorts to make speech. Even when you’re asleep, it’s constantly pushing saliva down the throat.
But arguably the strongest muscle, at least based upon its weight, is the masseter or primary jaw muscle. When all of the muscles of the jaw are working together, humans can apply a bite force up to 55 pounds on the incisors and more than 200 pounds on the molars.
That’s nothing compared to the maximum chomping power of Tyrannosaurus rex (12,800 pounds), of course, but it still would hurt.