3 Ab Exercises
Targeting the Rectus Abdominis
The Rectus Abdominins is the muscle in charge of PPT (posterior pelvic tilt) and spine flexion.
It’s a popular muscle to target for aesthetic reasons, and many trainees ask specifically to work in this muscle exactly for that purpose.
It’s important to remember it’s just one part of the abdominal muscles and not forget to strengthen and target the abdominal muscles as a whole.
In this post, you’ll learn the connection between the hips and spine, read how to avoid an unnecessary over spine flexion, and see anatomical analyses of 3 different exercises targeting the Rectus Abdominis.
1: Abdominal Crunches
This one is an all-time classic, maybe even the most popular ab exercise of all.
Disconnect your head and scapulae off the floor while keeping the lower back on the floor and the head supported by the hand.
➔ Exhale on your way up and inhale on your down
➔ For an endurance or stability workout, hold 6-7 seconds (isometric contraction).
➔ The intention is to activate the Rectus Abdominis and not produce explosive lumbar flexion in a full range of movement.
Anatomical Analysis of the Abdominal Crunches
The target muscles are the abdominal muscles. All four of them are active, but the focus of this exercise is on the Rectus Abdominis (red).
The obliques (pink) assist with flexion, and the transverse is pulled slightly inward to maintain intra-abdominal pressure.
Lateral view presenting spinal movement during sit-ups.
The loads on the lower back when performing variations of sit-ups:
A. Bent Knees (top)
B. Classic Sit Up (center)
C. Straight Legs (bottom)
According to the National Institute for Occupational Safety and Health (NIOSH), repetitive loading at or above this level is linked to higher rates of injury in workers.
According to McGill (2012), a full curl (elevating the head and shoulders far off the floor, A + C) is closer to replicating the higher stresses of the sit-up.
The intention is to activate the Rectus muscle and not produce lumbar spine motion.
The focus of flexion in this variation (partial curl-up) is limited to the thoracic spine.
If you nevertheless choose to do the full range of motion sit-ups, we recommend the straight leg variation (B) between the two examples presented above.
The reason is that straight legs stabilize the pelvis and do not allow it to rotate easily to the rear, thus preventing flattening or flexing of the lumbar spine.
2: Reverse Crunches
The Reverse Crunches are what their name suggests – they’re like the regular crunches, only that instead of disconnecting the scapulae off the floor, the pelvis disconnects. In other words, the thoracic spine is fixed, and the pelvis is free to move.
It’s the same spinal movement (flexion) which the Rectus Abdominis is in charge of.
Lay on your back with your arms to the sides, lift your legs at 90 degrees (bent or straight), and lift your pelvis off the floor by flexing the spine.
➔ You can press your hands against the floor for resistance if you want
➔ Make sure the movement occurs in the spine and not the hip
Anatomical Analysis of the Reverse Crunch
The target muscles are the abdominals, with an emphasis on the Rectus Abdominis.
The abdominals pull the pelvis up and stop the return stage to the ground.
The pelvis is pulled up by concentric contraction, and in the return stage, the abdominals are active in eccentric contraction. As noted, they prevent the pelvis from falling to the floor.
You can modify the level of difficulty by regulating the load:
Make it easier by bringing your legs (and the center of mass) closer to the movement axis,
and harder by keeping the knees over the pelvis and farther from the movement axis.
3: Jack Knife Crunch
1. Lie flat on an exercise mat, extending your arms straight back behind your head.
2. Bend your spine and, at the same time, raise your legs and arms to meet in a closed jackknife position.
➔ Exhale on your way up and inhale on your way down
➔ Make sure not to arch your back when lowering the leg
➔ Try to keep your neck in one line with your back
Anatomical Analysis of the Jack Knife Crunch
The target muscles are the abdominal muscles and the hip flexors.
The hip flexors connect the legs to the upper body and pull the legs up. These muscles also pull the pelvis anteriorly.
The abdominal muscles work hard statically to stabilize the pelvis and the spine and dynamically flex the spine.
We must maintain a neutral spine without allowing movement in the lumbar spine.
The leg weight draws the pelvis forward through the hip flexors.
The abdominals are supposed to stabilize the pelvis and prevent anterior tilt.
The abdominals work hard both statically to stabilize the spine and prevent lumbar movement and flexing the spine at the same time.
Strengthening your core is an important goal to have in every training session, and you can always add it to other exercises you do.
Every time you want to train a muscle, find different ways to make the target muscle activate in different ways by training different exercises in your workout routine. Remember – training all the abdominal muscles is crucial and, along with them, strengthening the back muscles as well.
Have a look at our abdominal bracing post to see how to engage your core deeply.
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