Abs are revealed in the kitchen, but they're built and strengthened in the gym. You can't uncover what's not there. And no, barbell squats and deadlifts don't activate the abdominal muscles better than targeted ab exercises. So get all that stuff out of your head right now.
That said, these five ab exercises are commonly done in a much less effective way than they should be. Here's how to avoid the common mistakes and get the most out of them.
You see it all the time in the gym, but this exercise doesn't make biomechanical sense. And many people do it by holding two dumbbells, one on each side. But the weight on one side offsets the weight on the other, making this exercise pretty ineffective at loading the lateral flexors of the torso.
The Right Way
Grab the handle of a cable (or resistance band) that has a low attachment, roughly ankle level with your right hand. Stand tall with your cable at your right side with your feet about shoulder-width apart. Make sure you're standing far enough away from the cable or band so that it's at roughly a 45-degree angle to the floor.
Without rotating your body, slightly bend your torso sideways to the right until you feel a mild stretch in the left side of your torso. Reverse the action and finish the rep by slightly flexing your torso to the left against the resistance.
There's not much resistance when you're standing upright holding a dumbbell because the dumbbell is very close to your body, giving you a huge mechanical advantage over the weight. But when doing them with a cable or stretch band, the angle of the cable forces you to work hard to stay upright and maintain that position between reps, giving you more time under tension through the range of motion.
Now, you could certainly hold very heavy dumbbells, but they may exceed your grip strength. You can create the same training effect with a cable and use much lower loads.
Whether you're hanging from a pull-up bar, have your elbows in those ab straps, or you're on a machine, the leg raise is a great exercise... if you do it right. But most people don't. They start with their legs hanging straight down then flex at their hips. That's mostly a hip flexor exercise, not an ab exercise.
The Right Way
Hang from a pull-up bar with an overhand grip and your hands roughly shoulder-width apart. Flex your hips and bend your knees, holding them above your hips in front of your torso.
In a controlled fashion, roll your torso upwards, bringing your knees toward your chin. Slowly reverse this motion without allowing your knees to become un-tucked from your body. Don't use momentum or jerk your body at any point.
Here's how it looks in a "captain's chair" machine:
The way these exercises are usually performed – with your legs hanging down and flexing at your hips – is primarily a hip flexion exercise. Although this certainly involves the abs, the degree of involvement is negligible. Tuck your pelvis and you'll target the abs better.
This is basically a less advanced version of the hanging leg raise. So if you're unable to perform hanging leg raises in the way described above (most people aren't strong enough), start with reverse crunches and progress from doing them on a flat bench and then doing them on an incline.
The Right Way
Lie on your back on a weight bench or on the floor with your knees bent and your hips flexed into your belly. With your elbows slightly bent, hold on to the bench just behind and above your head. If you're on the floor, hold on to a solid object above your head.
In a controlled fashion, perform a reverse crunch by rolling your lower back up off the floor and bringing your knees toward your chin. Don't use momentum or jerk your body. Slowly reverse this motion, lowering your spine back down one vertebra at a time. Don't allow your legs to extend or your head to lift off the ground at any point.
Make it even more difficult by doing it lying on an incline bench with your head higher than your legs.
Reducing any leg kicking forces your abs to do more work.
You see it all the time. Someone's lying on the floor on their back with their legs in the air and they're raising and lowering them. Sometimes they've got their hands jammed underneath their ass and other times their holding on to a partner's ankles.
Sometimes the gung-ho types have their training partner throw their legs back down toward the floor as they resist the force, which is the worst version of this move for most people.
The Right Way
Lie on your back on the floor with your knees bent, your hips flexed above 90 degrees, and your arms outstretched in front of your torso, just below shoulder level. In each hand, hold the handle of a resistance band that's attached to a stable structure behind you about 12 inches off the floor.
Maintaining tension against the band with your arms, slowly lower your legs toward the floor without allowing your lower back to come off the floor. When lowering your legs, start with the knees bent. Once your heels lightly touch the floor, reverse the motion and bring your knees back above your hips.
If it's too easy to lower your legs without allowing your lower back to arch off the floor while keeping your knees bent, simply extend your legs farther as you lower them. The farther you straighten your legs, the harder the exercise; the closer your heels are to your hips, the easier the exercise.
This version forces you to more efficiently use your abs to resist the weight. Plus, this version is more individualized to your strength level because it allows you to manipulate how much you extend your legs and how low you lower them without allowing the lower back to arch. Also, the band further enhances the muscle activation.
Allowing your lower back to arch off the floor reduces the involvement of your abs to resist spinal extension and places more stress on the lower back, which may end up increasing to the point of discomfort and increased risk of injury.
First off, many coaches and trainers want to claim that spinal flexion exercises like stability-ball crunches and reverse crunches are universally dangerous, which they believe is a claim based on Dr. Stuart McGill's research. They're wrong. Earlier this year (2017), Dr. McGill co-authored a paper on the crunch. Here's a snippet:
"If the ability to bear heavy loads is important to a client, it may be better to choose abdominal exercises with high muscular loads such as push-up position walkouts, rollout planks, or stir the pot. If flexibility is more important to the client, the personal trainer may want to select full-range curl-ups and crunches, and reduce heavy loading.
"If maximal muscular development is the primary goal, including the crunch and/or its numerous variations, together with other exercises, may help to enhance desired results. However, personal trainers should consider the entire exercise program, including cumulative tissue loading considerations and weigh the tradeoff between mobility and load-bearing ability."
In other words, spinal flexion exercises are no different than any other resistance training exercise. All exercises can induce stress, which causes tissue adaptation. From a back perspective, loading enhances tissue resiliency in general, but there's a tipping point when you exceed your capacity. That's the individual nature of training, and exactly what's meant by training smart!
The Right Way
Lie supine on a stability ball with the ball in the arch of your lower back and hold a weight plate, dumbbell, or medicine ball directly above your chest, arms outstretched.
Do a crunch, reaching towards the sky while holding the weight. Pause for one or two seconds at the top of each rep. Don't sit all the way up (with your torso perpendicular to the floor). That removes the tension from the abs.
Slowly reverse the motion, allowing your abs to stretch over the curvature of the ball. Don't allow your neck to hyperextend in the bottom position; keep it in a fairly neutral position throughout.
To focus on your abs when doing ball crunches, the ball shouldn't move under you at all. Instead, keep your knees bent at roughly a 90-degree angle throughout, and flex and extend your spine over the ball in a controlled manner. If the ball is rolling back and forth, it's primarily your knees (bending and extending) that are driving the motion, not your abs.
- Schoenfeld J et al. Choosing Exercises – "The Crunch". NSAC Personal Training Quarterly Journal. 2017 Apr;4(2).