Three Important Ab Exercises, by Greg Glassman - May 03 CFJ

Glute-ham Developer Sit-up
This situp is performed on the glute-ham developer. The range of motion is from as far back in hip and back extension as you are comfortable up to where you can touch the pads above the shin and instep.

Aerobics instructors and gym trainers typically disavow sit-ups like these because of a reputed harm to the lumbar spine by the tugging on the spine of the iliopsoas. It is further argued that this movement largely misses the abdominals because the primary mover is the hip flexors and not the abdominals. While correct that the primary mover of this sit-up is the hip flexors the notion that this is ineffective abdominal training is more gym-trainer rot.

When not accustomed to glute-ham sit-ups a single exposure of several sets yields an ab soreness that is truly impressive. This experience should hopefully dispel the notion that strong hip flexion sit-ups don’t target the abs.

Though the hip flexors (iliopsoas and rectus femoris) are the primary movers the abs play a strong role in stabilizing the torso to prevent hyperextension of the spine. (This is, in our opinion, a more functional role for the abs than trunk flexion.) We encourage the abdominal’s role in the glute ham sit-up by cueing the athlete to begin the movement by curling the torso upward.

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