There are two types of ab-crunch machines that you can usually find at your gym. The first is the seated machine that keeps you upright as you crunch, and the second is the lying version that places you in a back-lying position. Both machines primarily target the rectus abdominis muscle in your abs and your obliques at the sides of your torso. Add the ab-crunch machine exercise to the end of your full-body weight-training workouts or incorporate it into a more elaborate core-strengthening session.
Seated Ab-Crunch Machine
Adjust the height of the seat on the seated ab-crunch machine so that the front of your shoulders rest against the padded lever. Insert the pin into the weight stack to select the load you'd like to lift. Sit on the machine and lift your arms over the lever pad.
Exhale and flex your waist to push against he padded lever and bend forward at the waist. Keep your hips in the seat. Maintain a slow cadence, avoiding any jerky movement in an attempt to lift more weight.
Inhale as you extend your waist and return to a vertical sitting position. Once you return to upright, go right into the next repetition. Continue until you’re finished with all your repetitions.
Lying Ab-Crunch Machine
Lie on your back on the machine and adjust your position so that your head rests directly atop the head pad. Insert the pin into the weight stack to select the load you'd like to lift. Grip the bars that are positioned on either side of your face. Some lying ab-crunch machines have their handles positioned by the sides of your torso.
Exhale as you flex forward at the waist and raise the upper-back pad. Keep your hips firmly against the pad. The upward movement should be slow and steady rather than fast and jerky.
Inhale as you extend at the waist and lower the upper back pad so that it returns to the starting position. Go right into the next rep and continue until your entire set is completed.
Adding the Ab-Crunch Machine to Your Workouts
Do the ab-crunch exercise two to three days per week, allowing for one day off between sessions for your rectus abdominis and obliques to recover. If you’re adding the exercise to your full-body weight-training workouts, add it at the very end of your session so that your abdominals and obliques aren’t fatigued as you do your other exercises. Ab crunches can also be included in a core workout consisting of multiple abdominal and oblique exercises.
Complete two to three sets of the ab-crunch machine exercise, with each set consisting of 15 to 20 repetitions. Rest 60 to 90 seconds in between sets.
Use a weight that makes completing each set challenging. If you can complete 20 repetitions and you’re not fatigued, increase the amount of weight you’re using by five pounds. If you’re unable to complete 15 reps or find yourself having to jerk forward to finish them, lower the weight selected on the machine.