Machine Abdominal Crunches

Also known as: Ab Crunch Machine, Seated Ab Crunch Machine, Machine Crunch

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Body Part: Abs

Description

Sit in an ab crunch machine and curl your ribs down toward your pelvis to train your abs against a weight stack you can add to like any other lift. The rectus abdominis, your six-pack muscle, does the curling, and the obliques at the sides of your waist help. Your ankles are hooked under foot rollers and your chest pushes the pads of the machine arm, so your arms only hold on while your back rounds and your hips stay on the seat. The fixed path and small weight steps suit beginners and anyone who finds floor crunches awkward.

How to Perform

Set the pin in the stack. Go light the first time on a new machine, because crunch machines differ a lot in leverage.
Adjust the seat so that, sitting tall, the handles are about ear height and the padded bars rest on your lower chest.
Sit all the way back and slide your feet under the rollers so they rest on the front of your ankles, knees at about 90°.
Grab the handles beside your head with a full grip, elbows bent and pointing forward and down. Head neutral, eyes forward.
Breathe out and curl your ribs toward your pelvis, rounding from the upper back down. Your chest drives the pads; your arms just ride along.
Stop once your back is fully rounded and your elbows sit in front of your lower ribs. Squeeze a second, hips heavy on the seat.
Uncurl over 2–3 seconds to sitting tall, and start the next rep just before the plates touch down.
When you finish, let the stack settle completely before you take your hands off the handles.

What Muscles Work

Primary Muscle:

Tips

Take 2–4 sets of 10–20 reps close to failure; the seat and fixed path make hard sets safe. Pick a range such as 12–15 and add reps at the same pin until you get 15 on all sets with a full curl and a slow return. Then move the pin down one plate (usually 2.5–5 kg) and go back to 12. Compare weights only on the same machine.
Feel it down the front of your stomach, from just below the breastbone to below the navel, hardest at the bottom of the curl. Burning at the front of the hips or in the groin means you're folding at the hips; tired arms mean you're pulling the handles. Sharp pain in the lower back, or pain running into a leg, means stop.
New to crunches? Learn the curl on the floor with Abdominal Crunches first. When the machine gets easy, slow down to a 3-second return and a 2-second squeeze before you add weight or switch exercises.
Looking for oblique work? Here the obliques only assist; Seated Machine Trunk Rotation trains them directly.
Substitutes: Kneeling Cable Abs Crunches (longer range, heavier loads), Seated Ab Cable Crunch (the closest seated position), Weighted Ab Crunches (just a plate and a mat) and Weighted Decline Crunch (feet hooked under pads, as here).

Common Mistakes

Folding at the hips with a flat back. The trunk tips forward in one piece and you feel it at the front of the hips. Think ribs to pelvis, round your upper back first, and lower the weight until your spine actually curls.
Pulling the handles down with your arms and shoulders before your trunk moves. Lock the elbow angle and push the pads with your chest; your hands only hold on.
Driving your shins up into the rollers until your hips leave the seat. The rollers just keep you in place, so let them rest lightly on your ankles. If your hips still lift, the weight is too heavy.
Yanking your head down and jamming your chin into your chest. Keep about a fist of space under your chin and let your head follow your trunk, eyes on your knees at the bottom.
Dropping back fast and banging the plates on the stack between reps. Take 2–3 seconds to uncurl and start every rep from a standstill.