Although you are regularly bombarded with exercises claiming to tone and strengthen the abdominal muscles, many of these exercises are inadequate and ineffective. Some exercises may actually lead to lower back pain, and do little to strengthen the abdominals.
The ‘villains’ of abdominal training are the hip flexors, which bring the legs and trunk toward each other. Muscles that flex the hip include the psoas major, illiacus, rectus femoris, pectineus and sartorius. Full sit-ups involve the hip flexors, which may cause the lower back to arch and unwanted back pain, particularly in individuals with relatively weak abdominals. Leg-raising exercises in a supine position challenge the hip flexors with limited involvement of the abdominals. Frequently, there is a muscle imbalance between the weaker abdominals and the stronger hip flexors in trunk flexing movements. The goal of abdominal training is to maximize the involvement of the abdominals, while minimizing the involvement of the hip flexors.