Knee Raise Ab Coaster

Also known as: Ab Coaster, Kneeling Ab Machine, Knee Crunch Machine

CoreStrength

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Body Part: Abs

Description

Kneel on the ab coaster's moving pad, forearms on the arm rests, and drive your knees up toward your chest to train your lower abs against a load. You feel it most below the navel, with the whole front of your stomach and your obliques squeezed hard at the top. Your hip flexors help bring the knees through. Your torso rests on your forearms and the plate rides on the lever, so there's nothing to swing with and weight goes up in small steps. Pick it over captain's chair or hanging knee raises when you want to add load, or when your grip and shoulders quit before your abs.

How to Perform

Load the plate, or set the pin, while the platform rests at the bottom. Start light: the long lever makes even one plate feel heavy.
Kneel on the platform facing the arm pads, shins flat and knees at the front edge, with your feet hanging off the back.
Lean forward and lay your forearms along the pads, elbows at the back end under your shoulders, hands on the handles with palms facing in. Your torso ends up about 45° forward.
Press your forearms lightly into the pads, pull your shoulders away from your ears and keep your ribs down.
Breathe out and tuck your tailbone under first, then drive your knees forward and up toward your chest. The platform swings up with you.
Stop when your thighs are about level with your hips and your lower back has rounded. Hold for a second and squeeze your lower stomach.
Take 2–3 seconds to lower the platform to the start without letting the plate bang. After the last rep, let it settle at the bottom before you climb off.

What Muscles Work

Primary Muscle:

Tips

Near the end of a session, 2–4 sets of 12–20 reps work well, or 8–12 heavier reps with a full one-second hold at the top. Add reps first: once you get 20 on all sets with a full tuck and a 2–3 second lowering, add the smallest plate (usually 2.5 kg) or one stack plate, then build the reps back up.
Because the lever is long, one small plate can feel like a big jump. If your reps fall by more than 3–4, slow the lowering or add a 2-second pause at the top before adding weight. Too hard even with no plates? Stop when your knees are about halfway to hip height, and lengthen the range as you get stronger.
Most of the work should land below your navel. If it's mostly the front of your hips or your lower back, you're swinging the knees without curling the pelvis; if it's your shoulders or arms, you're pulling on the handles.
Substitutes: Captains Chair Knee Raises (same forearm support, bodyweight only, and kinder to knees that dislike kneeling under load), Hanging Knee Raises (much harder to keep still), Reverse Crunches (on the floor, the easiest way to learn the tuck) and Weighted Hanging Leg Raise (a big step up).

Common Mistakes

Throwing your knees forward from the hips and letting the plate carry the platform up. Start each rep from a dead stop at the bottom, tuck the pelvis first and take 1–2 seconds to lift.
Moving only the legs: the knees come forward but your pelvis never curls and your lower back stays arched. Think tailbone under, pubic bone toward the ribs. The rep ends when your lower back rounds, not when your knees stop.
Letting the plate drop and bounce at the bottom, or pull your thighs so far back that your lower back arches. Lower in 2–3 seconds, stop as the platform touches the rest and keep your ribs down.
Pulling on the handles and shrugging until your shoulders and arms tire before your abs. Push your forearms down into the pads and hold the handles just firmly enough to stay put.
Kneeling too far back, so your knees slide or your shins lift off the pad. Set your knees at the front edge with your shins flat before the first rep.