Abs respond to heavier weights because of their muscle fiber makeup. In order to get deeply etched abs, they also need to undergo some hypertrophy training. The rules on this are clear and, like every other muscle group, they require some form of progressive overload. Eccentric training can be a great way to achieve some extra load, as well as tap into those neglected high-threshold motor units (HTMU’s).
Your Abs Are An Endurance Muscle
There are around 35 different core muscles that attach to the spine and pelvis. We’re just going to talk about one. The rectus abdominis (aka your six-pack muscle) is more about the "show" than the "go." But if you want to strip the fat and unveil an athletic-looking mid-section there are a few things you should know about it.
The rectus abdominis is composed of roughly equal amounts of both slow and fast twitch fibers, built for both strength and power. Contrary to what some believe it’s not a muscle built for endurance, and therefore shouldn’t be trained like one.
To give you some context the soleus muscle in the lower calf is about 80% slow twitch. Genetics and training influence muscle fiber makeup, but even accounting for those outliers, 50% versus 80% slow twitch is a large difference.
This is just one of the reasons why the soleus responds well to higher repetition sets for hypertrophy, so spend more time in the 20-25 rep range. And, although you might feel your abs burning doing sets of 20-25 reps, they’ll more likely respond to a lower repetition range better. More like 10-15 reps per set, with the odd foray into the 6-8 rep range even.
Some research has also suggested that eccentric training can tap into the HTMU’s, causing preferential hypertrophy of the type II muscle fibers.
If you’ve spent a lot of time treating your six-pack like an endurance muscle and hitting those type I fibers, you’ll achieve greater abdominal development if you start increasing the weight and employing some eccentrics.
The Role of Spinal Flexion
The rectus abdomnis is designed to flex your spine and posteriorly tilt your pelvis. If you perform a crunch and simply think about closing the space between your ribcage and your pelvis, then you’ll be working your abs through their full range.
If you believe the spine only has a finite amount of flexions before you get a disk herniation that's not a problem. All we’ll say on that subject is that the spine is designed to flex, bend, rotate, adapt, and be resilient. To hit the rectus abdominis optimally, you need to flex.
This could be a topic for discussion in the comments though, but until then let’s move on.
Eccentrics Build Muscle
When muscle fibers eccentrically lengthen, they produce force because of both active and passive elements inside them. The passive elements are elastic-type structures that produce force by resisting deformation, rather than by using energy to move.
Because of structures that come in to play during eccentric contraction (extracellular matrix, the internal structure of the muscle fiber, and the giant molecule titin), we are usually 25-30% stronger when lowering a resistance than lifting it. Sometimes it’s not uncommon to be up to 40% stronger!
Eccentric training involves higher muscle forces, which can produce a large amount of mechanical tension and muscle damage. That’s two of the three proposed mechanisms that have been suggested as potent stimulators of muscle hypertrophy.
Providing that a larger load is used, or a longer time is spent focusing on the eccentric phase of an exercise, you may see greater muscle growth than typical concentric-eccentric lifting. There’s research to back this up, too.
There are three ways we could focus on loading the eccentric:
- Add extra load on the eccentric.
- Use the same weight, allowing you to do more reps when performed eccentrically.
- More eccentric time-under tension (TUT).
Of note, there’s little scientific evidence for or against focusing on eccentric TUT. But it makes sense from a mechanistic (and real-world) perspective that it would drive hypertrophy. If you don’t believe in spending four-seconds or more on the negative, then it should at least still be encouraged that you fight the resistance on the way down (two seconds or so).
Eccentric Abdominal Exercise Selection
Since you’ll be 25-30% stronger during the eccentric portion of a movement, you’ll be able to use more load or spend a longer amount of time there. That load can be in the form of external resistance, or by changing leverage factors so your body provides more load on the eccentric than concentric.
For example, arguably the most important thing to achieve in any knee or leg raise is the posteriorly tilted pelvis; that tuck of the pelvis as your knees get closer to your chest. It’s the portion of the movement where the fibers of the lower rectus abdominis massively come in to play and start to take over from the hip flexors.
Many achieve this position easier with a knee tuck rather than a straight-leg raise. Or at least due to the "easier" nature of the movement we can spend more time here. By raising with a bent-knee and lowering with a straight-knee, you’ll have added eccentric load starting from a posteriorly tilted pelvis at the top.
Performing the Garhammer Raise eccentrically is a good example. The Garhammer Raise was made popular by sports Scientist John Garhammer, PhD, and can effectively hit the lower rectus fibers.
If it’s a movement you can already do, by adapting it to an eccentric version of the same exercise you’ll complete more reps than normal, as well as more likely to have got closer to eccentric failure, rather than concentric fatigue.
If it’s a movement you can’t do yet, performing an eccentric version of it could be the bridging exercise you’re looking for to one day perform the full version with impeccable technique. Abdominal flags are a great example of this.
Trying to master ab wheel roll-outs from your toes? Try just the lowering portion off your toes, resist falling flat on your face, drop your knees, then perform the concentric as if you were doing the standard version off your knees. Reset to toes then go again.
Even performed eccentrically this is a great show of overall core strength, but worth it if done right.
You also have the option to just add eccentric load via an external weight. If you normally crunch with a 25lb plate overhead, give a 35lb plate a try. This time as you raise bring it in closer to your chest to lighten the load. The Sicilian crunch is an excellent example of this technique in action and really taps into those neglected fast-twitch fibers.
With many cable crunch variations, you can also execute a similar technique. Arms overhead increase the load due to a longer lever arm, while bringing your arms closer your chest shorten it.
A cable crunch will be harder when the cable attachment stays overhead during the lowering portion of the movement, and easier when brought closer into the shoulders or head in the lifting phase.
The standard kneeling cable crunch demonstrates such a technique. Do this with your butt back on your heels, or alternatively hips staying forward. Whichever technique you prefer, there’s an argument for either.
Finally, my a personal favorite. Using the same technique by changing leverage factors during the exercise, the incline eccentric cable crunch works a treat. It loads the eccentric very efficiently, while the incline bench and cable angle allow a constant tension throughout the movement.
Programming for Your Abdominals
If you want abs then you need to prioritize them. Throwing in a few sets of high-rep ab work at the end of your workouts isn’t going to cut it—our crappy diet isn’t either. If you haven’t already, drop your reps and start loading them. Eccentrics can be a great way to stimulate some hypertrophy whilst tapping into those HTMU's, too.
Try staggered ab training. Throw them in as a superset in between other exercises. If you’re going for a personal best deadlift then fatiguing your abs might not be a good idea, but super-setting with your lesser priority exercises can be a great way to increase your training density and even burn an extra few calories otherwise covering your abs.
You can also use staggered ab training alongside metabolic conditioning workouts. As a superset it works great to load your abs in between sets of prowler pulls, pushes, tire flips, farmer carries, battling ropes, kettlebell swings, and any other form of torture you prefer.
The point is, don’t leave them as an afterthought. Make them a key part of your workout and load them to grow them.
Granted, abs are made in the kitchen, but they’re forged in the gym!