The Golden Rules for Abdominal Exercises are:

  1. Isolate the abdominal muscles, and maximize their involvement.
  2. Minimize the involvement of other muscles, especially the hip flexors.
  3. Minimize the assistance of momentum.
  4. Have a specific abdominal exercise goal, such as endurance, strength, or range of movement, and exercise to achieve that specific goal.
  5. Don’t compromise the hips, back, or neck by performing the exercises too fast, or holding a position for more than a second, or twisting the back when in a flexed or extended position under load.
  6. If you can perform more than 20 repetitions of a particular abdominal exercise, then increase the intensity and do fewer repetitions.

There are six areas you should know about if you want to keep to these Golden Rules.

The average exerciser must bend their knees when trying to get their abdominal muscles involved in sit-up types of exercise. The best compromise for knee angle is 90 degrees, which means the hip angle is about 45 degrees.

Straight legs make it easier for the large hip flexor muscles to pull up your trunk when you sit up, rather than the abdominal muscles.

Straight legs provide a larger resistance arm for the legs and an increased moment of inertia in the legs, giving a good anchor for those hip flexor muscles.

Straight legs put the hip flexor muscles on a slight stretch, which increases their ability to get involved in getting your trunk off the floor and takes some of the work away from the abdominal muscles.

There are occasions when the legs can be straight, but these are specialized areas of either sports training or exercise rehabilitation, and should only be undertaken under the direct supervision of a trained and experienced individual exercise instructor.

Also, be careful not to have the legs too bent – a common problem we regularly see in exercise classes in gyms, such as aerobic floor classes or circuit classes.

If you tuck your heels right into your buttocks, then sure you’ll disadvantage the hip flexor muscles, but you’ll also reduce the range of movement of the abdominal muscles to such an extent that the only part of the abs that will get a workout are the bits at the top under your ribcage, not the middle and lower two thirds.

You’ll also be more likely to get a stiff and sore neck as your body involves muscles on the front and side of your neck, such as the sternocleidomastoid or the scalene.

As soon as you hook your feet under something or somebody holds your feet down, then you’re advantaging your hip flexor muscles and disadvantaging your abdominal muscles, for all the reasons already mentioned. The abs do less work, rather than more!

Then how come your abdominals are crying out in pain after only 30-seconds or so of feet held down sit-ups? The reason is that holding the feet down changes the role of the abdominals from pulling up in each sit-up to stabilizing the big bones in the pelvis. They are holding on like mad to your pelvis in one long, sustained contraction, and so they easily get fatigued. The hip flexor muscles do the real work of the sit-up.

What would you think of an exercise that asked you to hold a brick in your hand, and then lift that brick out to the side of your body and hold it for 30 seconds or so? Not much – try it and you’ll quickly experience fatigue and residual muscle soreness, but you won’t be helping your shoulder muscles get fitter. The same thing for the abdominals and feet held sit-ups.

Fatigue does not equal fitness. It is easy to fatigue a muscle, but this doesn’t induce the muscles to make adaptations and get stronger. Feet-supported sit-ups are not effective abdominal exercises and put the lower back under undesirable force.

The further away your arms are from your legs, then the harder the abdominals have to work. Put your hands on your knees and attempt a sit-up, and you’ll find it relatively easy. But put your hands on your head and you’ll find it hard to get up.

The theory is that moving your arms further away from the axis of rotation of the sit-up increases the length of the resistance arm of the upper body and the amount of inertia in the upper body. The outcome of this is that the abdominals now have to work harder to get you up.

If you’re finding it easier to do sit-ups, don’t increase the number of sit-ups, make it harder by moving your arms further up your body.

If you exercise in the gym there are lots of ways of safely increasing the resistance even more, using normal weight stacks and free weights as you would use for any other muscle in your body.

Any part of your body that swings forward as you perform a sit-up will generate momentum, and transfer that momentum to your body and make it easier to do a sit-up without using your abdominal muscles. Keep your arms close to your body and don’t let them swing. Don’t jerk up quickly, take it slowly, and use control.

While on the subject of arm and hand position, we would advise you to never lock your fingers together behind your head when performing sit-ups. This puts a lot of shear force on the fragile neck bones, and may lead to chronic neck and shoulder pain.

Sit-ups should be performed slowly and with control to allow the full range of movement of the spine and to allow the abdominal muscles to maximize their involvement in the exercise. Sit up too quickly and the arms flail forwards, legs straighten, and the back hyper-extends. There is an increased potential for injury and less abdominal involvement.

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