Every muscle in the human body has its specific function that allows humans to move the way we do. However, some muscles are more important in that they are activated more often, or are used in many different motions.
Transverse Abdominis
One of the lesser-known muscles, yet maybe the most important muscle in the human body, is the transverse abdominis. The transverse abdominis wraps around the mid section like a big belt (weight belts actually are supposed to mimic the action of this muscle). This muscle is so important because it is activated in virtually every movement humans make. The transverse abdominis is also activated to force expiration, compress and support the abdominal viscera, and increase intra-abdominal pressure.
Gluteus Maximus
The Gluteus maximus is the strongest, largest muscle in the human body. It is activated during hip extension, or straightening of the leg. Without the gluteus maximus, movements and actions like running, jumping, climbing stairs and lifting objects from the ground would be excessively difficult.
Latissimus Dorsi
The only muscle in the human body to connect the upper limbs with the lower limbs is the latissimus dorsi. The lower end of the muscle attaches at the pelvic girdle, with attachments along the spine, and the upper end attaching near the midline of the humerus (upper arm bone). This fan-shaped muscle is active during shoulder adduction, extension, internal rotation, transverse extension, and scapular depression, downward rotation and adduction.
Pectoralis Major
The pectoralis major, or chest, is another of the big, strong muscles of the human body. Its primary movement is to bring the arms together across the body (like giving a big hug). It is also critical for pushing objects away from the body (or the body away from an object, like doing a push-up).
Rectus Femoris
The rectus femoris is a part of two groups. While many know it is part of the quadriceps group responsible for extension of the knee, many don't know that it is also a part of the hip flexor group. The hip flexor group is responsible for lifting the leg, and bending at the waist. This muscle's versatility and functionality make it a major muscle in the human body.
