7. Standing dumbbell side bend
The standing dumbbell side bend was super-popular in the '90s and early '00s -- you'd see people cranking out the side bends in the free weight section of the gym like no one's business -- but eventually, the movement went out of style, and for good reason. Mainly because it's just not that functional; how often during your everyday life do you find yourself awkwardly leaning over to one side, then straightening up again?
People typically twist or rotate as they bend, engaging the core as a unit rather than trying to isolate the obliques. Plus, if you're trying to carve a six-pack, dumbbell side bends just aren't a good choice -- twisting exercises, like woodchops or bicycle crunches, are better options that target your obliques and your rectus abdominis.
6. Ab rocker and most ab machines
Two separate studies looked at the EMG response (electromyography, a typical test used to measure muscle and nerve activation) of the abdominals for various exercises, some of which used infomercial-style, popular ab equipment. The ab rocker, hands down, was the worst performer for oblique and rectus abdominis engagement in a 2001 study, while the bottom line from a 2014 study was basically that fancy ab machines and equipment are mostly unnecessary, given that you can enjoy significant muscular engagement with basic, equipment-free exercises.
5. Swiss ball pike
The swiss ball pike takes the challenge of a plank, adds instability and enhanced shoulder engagement in the form of the pike motion, ultimately creating one bad-ass ab exercise. Which, of course, is confirmed by science.
According to a 2010 study comparing it to the traditional crunch and bent-knee sit-up, the swiss ball pike came out on top for EMG activity of all the major muscle groups of the abdominals.
Granted, it's not easy to perform -- you need to have a fairly strong core and sufficient upper-body strength to control the movement without falling off the ball or collapsing to the floor. Start with a limited range of motion, only lifting your hips as high as you feel comfortable, gradually progressing to a full pike. You can also perform the same action with an Ab Wheel or TRX suspension straps.
The woodchop is the very definition of an integrated core exercise that works the abdominals through a twisting, reaching motion while also engaging the glutes and shoulders. According to a 2013 study, "When completing the core strength guidelines, an integrated routine that incorporates the activation of distal trunk musculature would be optimal in terms of maximizing strength, improving endurance, enhancing stability, reducing injury, and maintaining mobility."
In other words, if you want to improve core strength, you need to do exercises that require the engagement of the glutes and shoulders. The woodchop does just that, as do the other exercises included on this "best" list. Plus, the woodchop itself is excellent at working the obliques in addition to the rectus abdominis and transverse abdominis, really helping develop strength and definition throughout your core.
Start with a dumbbell or medicine ball version of the exercise, and as you get stronger, progress to a cable crossover or resistance band version with greater resistance.
3. Plank and plank variations
When it comes to enhancing core stabilization while targeting the deep, transverse abdominis, it's hard to beat the standard plank. Surprisingly, though, the isometric exercise is also effective at hitting the rectus abdominis (the six-pack muscle) and the obliques. Kendall likes it because, "You can do this movement practically anywhere, and it's easy to manipulate the degree of difficulty. If a regular plank is too easy, lift one arm or a leg. Try putting your forearms on a stability ball, or your feet in TRX straps. You can also take the plank to the side to better target the obliques -- the variations are endless!"
When incorporating planks into your workout, it's important to shoot for time, rather than reps. Kendall suggests you start by holding the move for 30 seconds, eventually working your way up to three sets of 60 seconds.
2. Ab wheel roll out
The ab wheel, admittedly, is a tough piece of equipment to use if you're just starting your fitness journey, but it's certainly effective. In fact, according to Kendall, "Ab Wheel or barbell ab roll-outs are, in my opinion, the most difficult ab exercise out there, but they come with the biggest payoff. This movement capitalizes on the concept of anti-extension; as you roll out, your trunk must work twice as hard to maintain a neutral spine without collapsing under your body weight and gravity. If you're new to this movement, start off on your knees. Once you're more comfortable with it, go up on your toes and try for three sets of 10 reps with minimal rest between sets."
1. Hanging leg raise
Kendall points to the hanging leg raise as the ultimate six-pack sculpting move, "Top to bottom, this is a great movement for abdominal development. There are several reasons why I like the hanging leg (or knee) raise for building a six-pack. For one, very little equipment is required -- all you need is a bar to hang from. Secondly, this exercise lends itself to multiple variations. You can scale them back by bringing your knees in toward your chest, rather than holding your legs out straight, or for added difficulty, you can hold a medicine ball or dumbbell between your knees or ankles."
Kendall's suggestion is also supported by research. Hanging knee-ups using straps were one of three exercises to elicit the greatest abdominal muscle response, as well as enhanced muscle response of extraneous muscle groups.
A note on "best" and "worst" ab exercises
Due to the, literally, hundreds of exercises people use to work their abs, even the most comprehensive studies that use EMG data to assess muscle activation during exercise just barely scratch the surface. This means many exercises and pieces of equipment haven't been studied at all, except through the anecdotal evidence of individuals who use them.
That said, evidence from a review study points to the importance of using multi-joint, free-weight exercises (think squats, lunges, pull-ups, pushups, and the like) to help strengthen the core, rather than relying solely on traditional core exercises. This evidence is compounded by another 2013 study that indicates the abdominal muscles engage more during exercises that simultaneously recruit the shoulders and glutes in an integrated routine.
The takeaway, then, is to stop thinking of your abs as a set of muscles you need to crank away at with hundreds of crunches to develop the six-pack of your dreams. Rather, they're a set of muscles inherently involved in almost all the exercises you perform, which means with proper core engagement, you can turn almost any free weight routine into a functional abdominal workout.