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A Myth Busted
Contrary to popular belief, crunches and sit-ups only tone the abdominal muscles, without causing any significant fat reduction.
Considering that we have a limited amount of time, that is devoted to physical training, we want to invest our strength into the most optimized and safest exercises, that can provide maximum gain. Gauging and comparing the effectiveness of certain exercises is therefore important. Two of the most standard exercises, aimed at strengthening the abdominal muscles are sit-ups and crunches, which are compared in the following lines, with respect to target muscles and technique, as well as the safety factor.

The Difference in Technique

Both exercises slightly differ in terms of execution technique. Here is a pictorial and textual explanation of the right technique.

Sit-ups
how to do sit-ups

First, let us see how to do a proper sit-up.
  • Lie on your back, on the floor (preferably on a mat).
  • Next, bend your knees in a 90 degree angle and place your feet, flat on the ground.
  • Place your hands on opposite shoulders, in such a way, that they are crossed over your chest or place your fingertips lightly at the back of your ear or head, without applying any pressure.
  • While your feet and butt are resting on the floor, slowly raise your torso off the ground and towards the thighs. During this step, tuck your head slightly forward, to lessen the engagement of the back muscles.
  • Rise until you reach a semi-seated position.
  • Then, go reverse and lower your back again to the starting position, as slowly as you can.
  • Do the whole exercise, as slowly as you can, without engaging in any jerky movements. This constitutes one sit-up.
Inhale, as you lower your torso and exhale, as you rise. Synchronizing your breathing with the workout, in this way, will help you benefit more from it. Some of you may need to anchor your feet to a fixed object or ask somebody to hold them, to prevent their movement, while engaging in this exercise.

Crunches

how to do crunches


Now, let us see how an abdominal crunch is done.
  • The starting position is same as the sit-up. Lie flat on your back, with knees bent in a 90 degree angle and feet, flat on the floor.
  • Place your hands, crossed over the chest or let your fingertips rest lightly behind the ear or back of the head. Do not exert force on the head.
  • Now, rise slightly to slowly curl your shoulders towards the pelvis, without lifting your lower back. Hold the position for a few seconds and then, return to the starting position. This constitutes one crunch. Inhale as you lower your body and exhale when raising it.
The essential difference between the two exercises is that crunches restrict movement to the shoulders and abdomen, without bringing the lower back into play.

The Targeted Muscles

The next point of comparison is the target muscles of the two exercises.

Targeted Muscles

Sit-ups primarily target the hip flexors, and the rectus abdominis muscle, as well as the tensor fasciae latae, iliopsoas, rectus femoris, and sartorius muscles. They also target the obliques to a lesser extent. On the other hand, crunches primarily target rectus abdominis.

Calories Burnt

Sit-ups burn more calories than crunches, but they also create more strain on the back, if the technique is not followed properly. Just sit-ups or crunches cannot cause spot reduction of fat. You need to supplement these with running and other cardiovascular exercises.

Health Risk

Crunches are safe exercises, which can be easily performed by anybody. However, sit-ups have an inherent risk of spine injury, due to the strain they put on the lower back, if pursued aggressively, with improper technique.

Those with a history of spinal or back problems should check with a certified medical practitioner before attempting both these exercises. When you plan to take up any one of them, it is better to get a proper demonstration of each exercise from a qualified trainer, or from someone who knows the technique well, before beginning.

Medical research on the dynamics of a sit-up has shown that the abdominal muscles are involved only in the first 30 degree raise of shoulders, off the ground. The rest of the strain is mostly taken up by the hip flexor muscles. That's why, many physiotherapists recommend crunches, as they are safer and more effective exercises, among the two types.

However, the opinion is divided about sit-ups. There are many practitioners who swear by it as an effective exercise, with no risk, if executed properly. You need not pit both exercises against each other and choose one. You can, instead, include both as part of your regular regimen to strengthen the mid-section. Just avoid extremes and increase your reps steadily. Take help from a qualified trainer to plan your muscle building program, according to your current physical status and medical history.