Iliopsoas, Lumbar Lordosis & Sit-Up Lower-Back Caution

Shortening of the iliopsoas (iliacus and psoas major) increases lumbar lordosis by pulling the lumbar curvature anteriorly; low-back strains may be felt — counter this with strong abdominals. This effect is seen in exercises such as straight-leg raises from zero to 45 degrees and hip flexions with a straight leg, and the iliopsoas contracts strongly in sit-ups, particularly if the hip is not flexed.

Traditional straight-leg sit-ups and leg raises work the hip flexors (iliacus and psoas — the iliopsoas), and if done with too much upward movement these sit-ups can lead to lower-back problems instead of abdominal tone. Although a bent-knee sit-up helps isolate the hip flexors to a degree, too much upward movement brings the hip flexors into play; the less a person rises during the sit-up, the less the hip flexors are recruited and the less force is applied to the lumbar spine (especially important for persons with underdeveloped abs). In abdominal training, ensure hip-flexor involvement is reduced to a minimum.

• A shortened iliopsoas increases lumbar lordosis and can cause low-back strain — counter with strong abs.
• Straight-leg raises (0–45°) and straight-leg hip flexions drive this effect.
• Straight-leg sit-ups/leg raises load the hip flexors; excessive upward movement can cause lower-back problems.
• Rising less during the sit-up reduces hip-flexor recruitment and lumbar-spine force.
• Minimize hip-flexor involvement in abdominal training.

• iliopsoas — the hip flexor that increases lordosis.
• hip-flexors — hip flexor group recruited by sit-ups.
• abdominals — strong abs counter the lordotic pull.
• rectus-abdominis — true trunk flexor for abdominal work.
• back-disorders-causes — posture/mechanics as back-disorder causes.
• abdominal-work-misconceptions — the "sit-ups/leg raises trim the waist" myth this mechanism corrects.