What Muscles Are You Working When Doing Sit-Ups?

by Kristin Dorman

About Kristin Dorman

Kristin Dorman has been writing since 1999 and has had work featured in "The Stylus," the University of Maryland's literary journal. She is a certified yoga instructor and teaches a "Yoga for Runners" course through community education. Dorman holds a Bachelor of Arts in studio art and art history from the University of Maryland, where she graduated with university and departmental honors.

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Situps are strength-building exercises that target your abdominal muscles and facilitate weight loss by burning calories. Do situps with proper alignment to reduce strain on your back and use other strength exercises and aerobic training for a well-rounded fitness regimen. Avoid tilting your pelvis or arching your spine during situps because this causes lower-back pain. Eat a low-calorie, balanced diet to burn fat and help tone your abdominal muscles.

Rectus Abdominis

Situps work your rectus abdominis, a superficial layer of major abdominal muscles. A sheet of connective tissue surrounds the muscles of the rectus abdominis, creating the six-pack look, though technically there are eight muscles, not six. The last pair of rectus abdominis muscles extend from your belly button down to your groin, so they are less noticeable than the top three pairs. Rectus abdominis muscles function to flex your torso in the upward phase of a situp and help control the speed of the downward phase.

Transverse Abdominis

Your transverse abdominis is the deepest layer of large abdominal muscles and has horizontal fibers that contract toward the center line of your body. Your transverse abdominis provides stability instead of flexion, contracting before you do a situp to prepare your torso for movement. According to the American Council on Exercise, researchers say the transverse abdominis provides feedback to your central nervous system before movements that potentially destabilize your spine.

External Obliques

Situps engage your obliques, which are superficial, lateral abdominal muscle layers. Your external obliques are on top of your rectus abdominis and have fibers pointing down and toward the center line of your body. Anatomy students imagine sliding their hands in their pockets to remember the direction of external oblique fibers. Your external obliques flex your vertebral column and compress the abdominal wall to support your internal organs.

Internal Obliques

Lying under the external obliques are the internal obliques, which connect to the lateral edge of your rectus abdominis. Internal obliques also assist flexion and support internal organs. Muscles fibers of your internal obliques run downward and away from the center line of your body, the opposite direction of external obliques. During situps, the sides of both your internal and external obliques work together to support trunk flexion, but also contract individually during trunk rotation.

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This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.