The frog crunch is a bodyweight abdominal isolation exercise performed lying on the back with the knees open and the soles touching, training the rectus abdominis with relaxed hip flexors. Letting the knees fall outward puts the hips in external rotation, which slackens the hip flexors so they cannot help lift the torso the way they do in a straight-leg or feet-flat crunch. The lift comes only from the abs curling the ribs toward the pelvis, and the range is short by design. Trainers use it as a beginnerabsexercise or as a finisher after heavier trunk work.
What Muscles Does the Frog Crunch Work?
- Primary: Rectus abdominis (upper abs)
- Secondary: External and internal obliques, transversus abdominis
- Tertiary: Hip external rotators, deep neck flexors, serratus anterior
How Do You Set Up for the Frog Crunch?
Lie on your back on a mat, bend your knees and let them fall open so the soles of your feet press together on the floor. Slide your feet toward your hips until the knees rest as low as your hips allow. Set your lower back flat, place your hands lightly behind your ears, tuck your chin slightly and lift your shoulder blades a finger's width off the floor.
How Do You Perform the Frog Crunch?
- Press the soles of your feet together and let the knees sink so the hips stay relaxed before the torso moves.
- Curl your ribs toward your pelvis, peeling the shoulder blades off the mat one segment at a time.
- Stop when your shoulder blades are fully clear and your lower back is still pressed into the floor; that is the top.
- Squeeze for one count, feeling the upper abs shorten while the knees stay wide.
- Lower slowly, laying the upper back down segment by segment until the shoulder blades are just off the mat.
- Pause with the blades hovering and the chin tucked, then begin the next curl.
What Are the Key Form Cues?
- Ribs to hips, not chin to knees: think of shortening the distance between your sternum and your belt line rather than sitting up.
- Knees stay heavy: let the knees sink toward the floor throughout, so the hips stay out of the movement.
- Keep a fist of space between your chin and your chest at the top.
- Exhale through the curl and feel the belly flatten as you rise.
- Keep the elbows wide and the hands light; they only hold the head.
What Are the Most Common Mistakes?
- Sitting up too far: once the lower back leaves the mat, the hip flexors take over and the abs stop shortening; stop as soon as the shoulder blades clear.
- Pulling on the head: the hands drag the neck into flexion and the deep neck flexors take the strain instead of the abs; keep the fingertips light behind the ears.
- Letting the knees drift together: the hips rotate inward and the hip flexors switch back on; keep the soles pressed and the knees open.
- Dropping back to the floor between reps: the rest unloads the abs at the bottom; keep the shoulder blades hovering.
- Rushing the reps with momentum: the shoulders bounce off the mat and the abs never get a full contraction; slow the lowering.
What Are the Best Frog Crunch Variations?
- Frog crunch with arms reaching: the hands slide up the thighs toward the knees, an easier version for beginners.
- Weighted frog crunch: a plate held on the chest adds load without changing the range.
- Frog crunch with legs raised: the soles press together in the air, so the lower abs hold the legs while the upper abs curl.
- Frog crunch with twist: curling one shoulder toward the opposite knee brings in the obliques.
- Stability ball frog crunch: the feet squeeze a ball, adding inner-thigh work.
How Do You Progress the Frog Crunch?
- Add a 5 to 10 pound plate on your chest once 20 clean reps with a full pause feel easy.
- Build from 12 reps to 20 per set before adding load.
- Add a fourth set when three no longer leave the upper abs burning.
- Slow the lowering to a three-count and hold the top for two seconds.
How Should You Program the Frog Crunch?
Place the frog crunch at the end of a session, after any loaded trunk work such as cable crunches or planks, two to three times a week. Work 3 to 4 sets of 12 to 20 reps with 30 to 45 seconds of rest, stopping each set when the range shortens. It pairs with a reverse crunch, which loads the lower abs the frog position leaves alone.