Why ab workouts shouldn't include this exercise...

Over the years, numerous routines and techniques have been promoted as a way to make your ab workouts more effective.

Some exercises work better than others. However, a Swedish research team has found one exercise included in many ab workouts that has virtually no effect on the abdominals.

Before you continue, it's important to keep in mind that there are many different abdominal muscles.

In this study, the term "abdominals" refers to rectus abdominis, along with the external and internal obliques. Learn more about the abdominal muscles (pop-up window).

As part of their study, researchers from Stockholm's Karolinska Institute compared the double leg raise with the single leg raise using electromyography (known simply as EMG). EMG can be used to measure muscle recruitment during various exercises.

Surface electrodes were placed on the skin over the rectus abdominis, obliquus externus, obliquus internus, rectus femoris, and sartorius muscles and with indwelling fine-wire electrodes from the iliacus muscle.

The double leg raise, which involves raising both legs from the floor at the same time, was found to activate both the abdominal muscles and the hip flexors.

The single leg raise involves raising just one leg from the floor. Although it activates the hip flexors, the results show that the single leg raise requires virtually no work from the abdominals at all!

The question is, why?

During the double leg raise, the abdominals work to keep your pelvis "stable".

However, the fact that the other leg rests on the floor during the single leg raise appears to be enough to stabilize the pelvis while the other leg is lifted.

The result is that the single leg raise requires very little work from the abdominal muscles. Unless you've been told otherwise by a therapist, it's probably best to leave this exercise out of your ab workouts.

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References
1. Andersson, E.A., Nilsson, J., Ma, Zhijia, M., & Thorstensson, A. (1997). Abdominal and hip flexor muscle activation during various training exercises. European Journal of Applied Physiology and Occupational Physiology, 75, 115-123