There are many myths that surround ab training. Some old favourites such as high rep sit ups or crunches, using a Swiss ball for core stability, abs only being built in the kitchen or abs being unnecessary if you do heavy compounds. I believe all of these to be false and that good abs are the result of heavy strength work combined with the correct diet. The symmetry of your abs is beyond your control but the thickness of them is not.
Big strong abs will make you stronger. You will feel like an immovable object as well as giving you an awesome physique.
There may be lots of skinny guys out there who have abs and don't train but you can really tell the difference between one of these guys and someone with exceptionally strong abs. Just like any other muscle the abs can hypertrophy and increase in size and thickness with training. The skinny guys abs are typically flat and small and merely exaggerate their already skinny look.
The abs main purpose is stability of the spine as opposed to bending it. So exercises which require a great amount of stabilisation are the best to develop functional strength in the abs. Heavy strength work seems to be the way to go here and I believe the abs develop best under high load low rep exercisers rather than traditional bodybuilding rep schemes. This may be due to them being more fast twitch dominant muscles used to protect the spine under stress rather than needing a sustained contraction. There are other muscles I feel fall into this category such as traps but that is a different article altogether.
So I feel that high rep exercises like sit ups and crunches are a waste of time for abdominal development because they aren't working the abs in their main function and aren't difficult enough to stress the abs in the way they develop best. Another exercise which seems to be massively popular for no reason I can work out is the cable crunch. Basically you either use a lightweight a do a billion reps same as sit ups or try to use a heavy weight and realise it doesn't really work due to the counter balance of your own bodyweight. The only thing I have found them useful for is as a rehabilitation exercise for back injuries or to just throw in if your back is feeling a bit beat up such as after sets of heavy deadlifts.
Next we have the plank. While moving in the right direction in terms of abdominal function it is not heavy enough to work to abs best for development. For most people it needs to be held over the one minute mark and just becomes an exercise in willpower rather than statuesque ab development. But the plank does have some close cousins which are effective ab exercises.
Before we discuss the truly useful abdominal exercises let's first clear up a couple of things. "Abs are built in the kitchen" not entirely true. Yes you need to be lean to see your abs but the abs need to be developed and hypertrophy combined with low body fat otherwise you end up with skinny looking abs rather than blocks of steel. "If you lift heavy you don't need to train abs" this may be partly true. While doing heavy compounds such as squats, deadlifts, and overhead presses the abs are working hard to stabilise the spine and they are being used for low reps. The only problem is the abs aren't being trained to their full potential. How many times have you had really sore abs after doing some compound lifts? Probably not very often even when the prime movers are sore as hell. This should tell you that the abs aren't being trained as fully as they should be.
So let's look at some effective exercises for the abs. First we have kneeling ab wheel rollouts. These are basically the plank in motion and are the beginning stage of effective ab work. They are working the abs in a stabilising role and are difficult enough for most beginners to get heavy enough response needed for greater ab development. Once full range of motion is used with arms full extended it doesn't take long for these to become too easy with a more difficult version required. Start with 5x5 twice a week and add reps up to 5x10. Then its time to move on. The next progression is the standing ab rollout. These are very difficult and can be built up to by using standing rollouts on an incline or doing partial standing rollouts. However I have found weighted vest kneeling rollouts to be incredibly effective allowing me to add steady increases by adding weight to the vest. These let you still train the fully extended range of motion which is the hardest part of the standing rollout allowing you to builds up gradually to them. Once standing rollouts have been achieved they can be made harder with a weight vest and declines and your abs would be pretty insane by that point.
The next idea for building brutal abs is the use of heavy partials in your training. Heavy partials such as rack pulls and rack squats overload the stabilisers during the lift by allowing you to handle weights much heavier than the full range movement. The prime movers no longer become the limiting factor but maintaining stability through your abs, obliques and lower back is. The best movements to use are rack pulls from various heights, rack squats where you set the bar up on the power rack pins duck underneath it and stand up and overhead press lockouts. The lockouts will depend on the height of your rack. If your rack is too short you can try loading the bar on top of the power rack frame but be very careful with this and don't try it in a commercial gym. The other option is kneeling overhead lockouts which offer almost the same benefits. Use low reps or singles and build the weights up slowly. Its easy to get injured doing heavy partials too soon.
Some other options for building epic core and ab strength are gymnastic progressions which require a lot of core strength to hold the positions. You can start at relatively easy movements and progress to more difficult variations. There are 3 main movements I'm thinking of to practise. L seats, dragon flags and front levers. For L seats think of holding yourself in a dip position and raising your legs up to 90° so you are in an L shape. This is like an isometric leg raise. Do timed holds and try to increase the time you can hold them. You can progress to V sits where you lean back slightly and raise and your legs up higher. This does require good hamstring flexibility. Beyond this is what's known as the Manna where you hold your body parallel to the floor with legs flat against your face. They are an elite gymnastic exercise and beyond the reach of most people.
Front levers involve hanging from a pull up bar and holding your body out horizontally. They require tremendous core and lat strength to do. You can build up to them by starting off holding the position with you legs tucked into you body. You can progress to holding your legs out further and further. You can do one leg straight and one leg tucked which are considerably easier than the full version. Lastly there is the straddle version where you split your legs as far as possible to make it easier than holding the legs out straight.
When it comes to building strength and thickness of the midsection an often overlooked aspect are the Obliques. For a long time training the obliques was actively discouraged with people thinking it would make your waist appear thicker and ruin your V taper. I feel this is wrong as you won't add a huge amount of muscle to your waist by training your obliques and well developed and defined obliques make your waist look far more impressive than the smoothness of no oblique development. From a functional perspective a strong set of obliques are powerful spine stabilisers to improve strength and avoid injury. I recall seeing a guy in a old gym once doing endless broomstick twists because he said it would help define his waist without making it bigger. This is just nonsense. If you want a defined waist combine diet with effective ab training.
There are 3 useful oblique exercises that I can think of. The first are dumbbell side bends. Hold a dumbbell in one hand bend down to the side and straighten up again. Very simple and quite effective. You will probably find you can handle fairly reasonable weights in this exercise with dumbbells exceeding 50kg not taking long to surpass. This goes to show you how strong the obliques are. Doing sets of 6-12 reps works best for this exercise. Next we have a deceptively hard exercise known as Saxon side bends named after the old time strongman Arthur Saxon. To do these take 2 light dumbbells (and I do mean light) no more than 5kgs to begin with and press then overhead. Now perform a side bend keeping your arms parallel and in line with your torso. So as your torso bends to 45° your arms and the dumbbells should follow it. Then straighten up back to the centre. You will find the stabilisation needed is incredible to perform this exercise. For these I would go for 5-10 reps per set each side.
Finally there is the suitcase deadlift. These are basically a one handed deadlift with the bar perpendicular to you at your side like you would carry a suitcase. They require tremendous oblique strength during the deadlift to maintain the upright position. But the problems with this exercise is balancing the bar when using a standard Olympic bar. If you don't get the hand position exactly right the bar will be unbalanced and drift forward or backward usually resulting in one end crashing to the ground. I found I would have more bad reps than I would good reps with this exercise so a few adjustments have to be made. Suitcase rack pulls have been suggested with a higher start position the lift feels more oblique heavy by removing much of your legs from the movement. But the unbalancing of the bar is still an issue. To solve this problem there are a few options. In a standard gym with standard equipment you can use either an EZ curl bar by holding the centre bend of the bar offering better balance than a straight bar or use a tricep bar on its side with also offers a slightly higher start position. If you have access to one you can use a cambered bar or one side of a farmers walk bar which I have took to using. The raised handle allows the bar balance while raising the start position to make it more targeted on the obliques. Low reps of 1-5 work best for this. In terms of weights to aim for I think double bodyweight would be a good goal if grip isn't an issue (you could always use straps. Its not a grip exercise). While you could do these with a dumbbell or kettle bell I don't think its a great idea. You won't be able to go heavy enough and the dumbbell puts you in a very low awkward position which I believe losses the effectiveness of the exercise.
The final training method for developing a thick strong core is lifting and carrying heavy awkward objects. Objects such as rocks, sandbags, logs, and barrels. Lifting these objects in any exercise calls into play many stabilising muscles of the midsection in order to handle the bulk and awkwardness of these implements. The bulk of the objects makes them further away from your centre of gravity making the lift more difficult. Also their tendency to move such as sandbags or water filled barrels causes you to make constant adjustments as you lift them. These objects don't want to move in a straight line like a barbell does which makes them so great at developing the core. What you do depends on what you have access to. For sandbags you can buy the outer bags specially made for sandbags from PullumSports but they are a tad expensive. What I did was buy an old army duffel bag from a Army Surplus shop for £10. I then went to B&Q and bought 4x20kg bags of builders sand and some heavy duty black sacks. I lined the bag with the sacks and then added 3 bags of sand. I then gaffa taped up the sack and tied the bag up with rope and tape. That gave me a 60kg bag with the option of adding another 20kg to it a some point. I obtained a Keg from a friend of a friend who owns a pub. I half filled it with water and it is incredibly awkward to lift. I'm not sure how else to get one of these but I have seen plenty lying around in alleyways. Perhaps a scrapyard could get you one. For stones and logs you can buy ready made strongman versions from Pullum sports and other places online. Or builders yards or garden centres could also sell you then. Of course there is always nature with a fine selection of rocks at my local beach and many logs in the forest. What you do with these things is up to you there are almost endless exercises and combinations depending on what you have. Clean and presses, Shouldering, carrying in the arms, carrying on the shoulder, deadlifts, complexes, loading medleys, lunges with them on the shoulder, get ups with them on the chest, power cleans, power curls, zercher lifts and carries, throwing them etc. I won't go into sets and reps that's up to you but these work great as finishers at the end of a workout.
That gives you lots of options for ab training. Now I don't suggest you try to do everything at once but pick one or two exercises or methods to try. Some work your abs indirectly on top of others things such as partials, front levers and odd objects while others isolate your abs more. What you do is dependant on your strength levels, goals and access to equipment. There are no six pack shortcuts or secrets but I do believe a lot of conventionally ab training is ineffective. Try these ideas and see for your self what it takes to build and iron midsection.