Crunch

Active muscles:

Abdomen:

• Rectus abdominis (straight abdominal muscle)
• Obliquus externus abdominis (external oblique abdominal muscle)
• Obliquus internus abdominis (internal oblique abdominal muscle)
• Musculus transversus abdominis (transverse abdominal muscle, or ‘corset muscle’)

Pelvis (depending on execution):

• Psoas major
• Iliacus

Legs (depending on execution):

• Rectus femoris
• Sartorius

For a six-pack or injury prevention?

Strong abdominal muscles are essential for a strong core and preventing, among other things, lower back pain. In practice, many people do abdominal exercises mainly for a better-looking abdomen. Often with a tight stomach or six-pack as the ultimate goal. In most cases, you do not need to do abdominal exercises for a flat stomach or six-pack. These are mainly caused by a low body-fat percentage. You cannot specifically burn fat in the abdominal region, not even with abdominal exercises. A six-pack is therefore mainly made in the kitchen, as the old saying goes.

At a low body-fat percentage, abdominal exercises can make a visual difference. Thicker muscle bellies in the rectus abdominis then create deeper lines in the abdomen. However, the abdominal muscles are used and therefore trained during many different exercises and daily activities. For most people, a low body-fat percentage is therefore enough for a six-pack. In some exceptional cases, the muscle bellies (the ‘blocks’) in the rectus abdominis are so flat that they are barely visible. Even at a low body-fat percentage. Very superficial tendinous intersections and a linea alba that divides the muscle bellies can also contribute to this. In those cases, doing abdominal exercises for appearance may be worthwhile.

Training the abdominal muscles for a slim waist?

However, the abdomen can be viewed not only from the front, but also from the side. The transverse abdominal muscles on the sides draw the abdominal wall inward and thereby prevent the abdomen from protruding. These transverse abdominal muscles are also active during abdominal exercises. Training them as well could therefore reduce your waist circumference. Like a corset being tightened.

At the same time, however, the muscle bellies of the rectus abdominis become thicker. This creates deeper lines when viewed from the front, but also causes the abdomen to protrude farther when viewed from the side.

Training the abdomen or the legs?

During abdominal training, muscles in the pelvis and upper legs are often also engaged unconsciously. The rectus femoris is one of the quadriceps muscles. It is the only quadriceps muscle that crosses not only the knee joint, but also the hip joint.

The rectus femoris brings the thigh toward the pelvis and the lower part of the spine, and vice versa. It is what is known as a hip flexor and therefore brings the thigh forward from the hip joint. This also happens when the torso is brought too far toward the thigh during an abdominal crunch, causing it to start resembling a sit-up. The weaker sartorius assists the rectus femoris in this.

Shorter muscles that connect the pelvis to the thigh, the psoas major and iliacus, also play an important role in flexion at the hip.

During the abdominal crunch, therefore, focus on curving the spine (as if you were being punched in the stomach). When you lift the entire torso, you begin to engage the aforementioned muscles in the pelvis and upper legs more. Moreover, the higher you come, the less active the abdominal muscles become. This is one of the reasons crunches have become more popular than sit-ups over the years.

Hands on the chest or behind the head?

The abdominal crunch is often performed with the forearms crossed over the chest or with the hands behind the head. In terms of abdominal muscle engagement, this makes little difference. However, with the hands behind the head, you may be more inclined to also flex from the neck (bringing the chin toward the chest). Keeping the hands on the chest therefore makes it easier to maintain the correct posture during the exercise.

• Crunches (arms down)
• Sit-ups
• Crunch machine
• Cable kneeling crunch
• Ball crunch