Abdominal Crunch

A seated abdominal crunch is an exercise, which involves the abdominal muscles, primarily the rectus abdominis. This exercise is performed seated on a machine. The concentric portion of the exercise is flexion of the vertebral column. The eccentric portion is extension of the vertebral column.

The purpose of seated abdominal crunches is to strengthen the abdominal muscles while promoting the hypertrophy (increases in size) of this muscle group.

Promoting hypertrophy of the abdominal muscles with trunk flexion helps define the “6-pack” of the rectus abdominis. Strengthening the abdominal muscles offers protective effects for the lower back as the abdominals play a role in stabilizing the torso. Stronger abdominals also complement exercise and sports performance as they can contribute to biomechanical efficiency during physical activity and exercise. The resistance of the machine elicits oblique activation throughout the entire range of motion.

The abdominal wall is made up of broad, flat sheet-like muscles that are layered. The rectus abdominis is a vertical muscle that extends from the pubic crest and symphysis (at the pelvis) to the rib cage (xiphoid process and costal cartilages of ribs 5-7). The rectus abdominis is segmented by three tendinous intersections that run horizontally across the rectus abdominis. This tendon outlines the “6-pack” of the rectus abdominis along with the linea alba, a tendinous seam that runs down vertically, dividing the “6-pack” in half.

The oblique muscles assist the rectus abdominis with flexion of the vertebral column. The external oblique muscle runs downward and medially and forms the inguinal ligament of the groin area. Its origin is at the outer surfaces of the lower eight ribs and it inserts into the linea alba via a broad aponeurosis. Some of the fibers of the external oblique insert into the pubic crest and iliac crest.

The internal oblique, as its name suggests, is located below the superficial external oblique. Its fibers run in an upward and medial direction. Its origin is located at lumbar fascia, iliac crest and inguinal ligament. Its insertion is located at the linea alba, the pubic crest and the last three or four ribs.

The transverse abdominis is the deepest muscle of the abdominal wall with fibers running horizontally. This stabilizing muscle compresses the abdominal contents. Its origin is located at the inguinal ligament, lumbar fascia, iliac crest and the cartilage of the last six ribs. It inserts at the linea alba and the pubic crest.

Abdominal crunches, Cable crunches.

The abdominal muscles are working all day, every day, when you are physically active. For example, the rectus abdominis stabilizes the pelvis when you’re walking. Therefore, a greater overload stimulus is required to stimulate growth of the abdominals when isolating them during exercise. This machine, however, is limited in its benefit and activation of the abdominals. The resisted motion within the confines of the machine can also place the spine in a compromising position as the vertebral column extends to starting position. It’s important to note that this exercise should be performed with a light weight to prevent risk of injury.

Incorporating various abdominal exercises complements the performance of seated abdominal crunches, especially as you advance in exercise difficulty (e.g. V-ups, hanging leg raises).

Focus on each concentric portion of the contraction, concentrating on “squeezing” as the torso is flexed.

Emphasis on eccentric contractions, prolonging the descent phase back to the mat, may also be incorporated with an abdominal training program focused on increasing strength. This should be implemented accordingly and with adequate muscle recovery as eccentric contractions cause substantial damage to muscle tissue and/or delayed onset muscle soreness (DOMS).

It’s important to note that your repetition and set volume will depend on your goals (e.g. strength, hypertrophy, muscular endurance). Strategically varying your intensity, rest times and volume (number of repetitions in a set) will optimize abdominal development with time.

Returning the weight to the starting position too quickly can threaten the integrity of the spine. It is important to control the concentric and eccentric portions of this exercise.

It is important to note that exercise machines, in general, may not accommodate ergonomically to the varying heights, torso lengths and limb lengths of individuals. Adjust the seating pad and arm bar height accordingly. Ensure that you do not compromise the safety of your back against the weighted resistance.

When incorporating abdominal training into your exercise regimen it is important to evaluate what other exercises you are doing in that training session. For example, it may not be best to train abdominals on the same day as performing deadlifts and squats as those exercises fatigue the abdominals substantially. Training abdominals before or after a training session that involves smaller muscle groups (e.g. calves, biceps and triceps) may be suitable, as it will not interfere with the quality of the overall training session.

While performing abdominal exercises with added resistance can improve strength gains, increasing the weight beyond the lifter’s capacity can result in injury to the back or abdominal tissue.