Key Points
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Crunches work your abs, which are significant in most body movements.
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Crunches are simple; simplicity yields stellar results — if you play your cards right.
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Spot reduction is a myth; crunches alone won't help you lose body fat.
Crunches are the most common exercise the average gymgoer thinks of when they think about weight loss goals and getting stronger. In a tie for second place, there is also running.
But that's not why you're here.
Unfortunately, crunches also have a mythic status in the fitness world; that status is often not good one. Some argue that they are useless altogether, but nothing is so cut and dry with exercise.
Your Spine
The human spine is important for many reasons, and you typically tend to notice how important it is when your back hurts. Considering the spine and all that it's capable of when you exercise is important since nobody wants back pain of any kind. With that in mind, knowing what your spine does is the first step to protecting it.
Spinal Composition
Human spines have three parts, all connecting in a curvy line. Those three segments are your lumber (your lower back), the cervical spine (your neck), and the thoracic spine (your upper back).
The spinal column consists of a group of bones called the vertebrae, and in between each of those bones, you have a disc that provides cushion to absorb the compressions and shocks you deal with while living life as a human.
Your lumbar has five vertebrae, your thoracic spine clocks in at 12, and your cervical spine has seven of those bones.
Functionality
Think of the bones of your spine as a collection of small joints. After some simple math, you conclude you have 24 small joints comprising your spine. The functionality of joints is simple: They move. Specifically, they move because the muscles attached to them make them move.
Extension
The extension is one such movement your spine produces. Put simply, extension is leaning back. If you've ever done yoga or witnessed someone doing yoga, the cobra is an example of spinal extension. Any movement where your shoulder blades gain proximity to your pelvis involves extending the spine.
Forward Flexion
The opposite of spinal extension, forward flexion is the motion you make when performing a crunch. Any motion involving bringing your chest closer to your pelvis is forward flexion. Tying your shoes, picking up your overstuffed wallet, and touching your toes to stretch all qualify.
Lateral Flexion
In addition to the front and back motions, your spine also moves side to side. Stand up straight, arms at your sides. Slide your hand down the side of your leg, and you'll find yourself in a side bend. There's your lateral flexion.
Lateral Extension
From that side bend position, straighten yourself out. There's your lateral extension. The difference between the two of them is your starting and end point. If there's a weight involved, then the difference also involves which direction moves against the resistance.
Rotation
Finally, spines rotate. Swinging a bat, a golf club, or a hockey stick are examples of spinal rotation. You rotate to the left and right.
Segments
As mentioned, the spine has three segments. Generally, these segments move in unison with each other to varying degrees. However, these motions may occur independently in each section.
Core Musculature
There's not a unanimous definition of "the core." Usually, people assume it refers to the abdominals, which is a good start. Other definitions include the head and/or the pelvis. For simplicity, the core refers to your spine and the surrounding musculature.
Your back has a major muscle group called the erector spinae, commonly called the "spinal erectors," which controls your spinal forward flexion and extension on the thoracic spine.
Up front, you have the abdominal muscles, which are:
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Internal and external obliques
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Transverse abdominals
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Rectus abdominals
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Psoas Major
There are more, but this isn't an anatomy textbook, so the previously listed muscles are pertinent.
Your obliques rotate your spine and laterally flex it; your rectus and transverse abdominals flex it forward. The psoas, which attaches to your femur and the bottom of your thoracic spine, flexes your hip.
That's not a complete view of your core, but it's enough for a gymgoer to concoct a decent ab workout.
Protection
In addition to moving your spine, your core musculature also affords a level of protection to your spine by not moving. In the biz, it's called "stabilization." Your deeper abdominal muscles, like the internal obliques and transverse abdominals, help keep it stable.
Exercises like planks and pallof presses aid in stabilizing your spine, and that stabilization protects your spine against impacts and sudden movements.
What Is A Crunch?
A crunch is a simple abdominal exercise. Lie on the ground, knees bent, feet on the floor, and press your lower back into it. Raise your chest, directing it toward your thighs, and you've done a crunch. You're simply flexing your abs to move your spine forward in flexion, mainly with the rectus and transverse abdominals.
In its simplest form, that's a crunch. However, add many variants to your repertoire to make them more challenging or provide a more sport-specific practice.
It's Definitely Not A Sit-Up
Sit-ups are commonplace in PE classes, and some military fitness tests also incorporate them. Like crunches, sit-ups work your abs, though they do so in a different way.
To perform a sit-up, lie on the floor as you did for your crunches, but this time, secure your feet. A good option to keep your feet where they are is to have a friend hold them. If you have no friends, a heavy object on top of your feet does the trick, or use one of the specific sit-up implements at your gym if they have such devices.
Instead of flexing your abs and limiting how much you move, you keep your torso still. Your feet press upward while you press your butt downward, and your stable torso rises.
Unlike the standard crunch, a sit-up stabilizes most of your abdominal muscles, allowing you to work the psoas, directly flexing the hip.
In short, both the crunch and the sit-up train your abs, but they do so in different ways. The sit-up stabilizes most of your musculature except for the hip flexors, and the crunch directly targets the other muscles by flexing them.
Crunches, Variants, and Performing Them
Previously, you read a description of the most basic form of the crunch. Lie on the floor, flex your abs, and repeat often. Basic though it is, it's worth attaining an above-average level of proficiency in order to modify them accordingly
With two other considerations, mastery of the basic crunch is easy. If you ever were lucky (or unlucky) enough to see the late-night commercials for various ab machines in the 90s, one of the benefits the marketers touted was the design of the machine as a way to reduce neck pain.
Typically, people tend to lace their fingers behind their heads while performing this exercise, and if you're not thinking about it, the hand position allows you to crank your neck. Instead of flexing solely with your ab muscles, you're cranking on your neck to get to the endpoint of the range of motion. Having your hands on your head isn't good or bad, but cranking your neck and causing pain is something to avoid.
One way to limit this is to perform the "Wakanda Forever" salute by crossing your arms over your chest.
Another way is to imagine you're reaching the tip of your nose to the ceiling. Your cervical spine stays uncranked, and you'll work only your abs.
Reverse Crunches
Once you are comfortable with the performance of the basic crunch, it's time for your following variant. One of the most ubiquitous crunch variants is the reverse crunch. The goal is the same as far as flexing your abs, but this variation gives you the added benefit of targeting your psoas while keeping your upper body stationary.
Assume the crunch position, but this time put your hands under your butt as you lie down. Keep the knees bent, lift your feet off the ground, and bring your knees towards your face per your physical comfort levels.
Your low back rises, resulting in the abdominal flexion you desire. Lower your feet back to the starting position while keeping control of their descent. Don't let gravity do the work here.
Bicycle Crunches
This modification is a hero in every cinematic exercise montage. Bicycle crunches, like reverse crunches, target the psoas along with your abs but also target the obliques.
Your starting position is slightly different from the previous two. Lie on the floor as usual, then lift and flex your feet so your soles point toward the wall. Calves should be parallel to the floor and your hips at a 90-degree angle. Finally, cross your arms over your chest.
Perform a crunch and imagine you're reaching towards your left knee with your right elbow. At the same time, bring your knee towards you.
If done correctly, you'll twist as you reach for your knee. Return to your neutral position, and mirror that same action by reaching with your left elbow to your right knee and bringing that knee towards you.
Done in succession and with minimal pausing in between reps, your legs mimic the motion of pedaling a bicycle.
Weighted Crunches
Your abs are muscles. Like all other muscles, it's possible to contract and flex them with added weight. Before trying this modification, make sure you master the basics. Weight crunches also come in different forms.
Machine Crunches
Commercial gyms often have different machines that allow you to perform a crunch with resistance. The general idea of the machine is the same for each of them, but the mechanisms that allow you to crunch differ from one machine to the other.
Some crunch machines have a place for your head and handles nearby to grab. Other machines have a bar going across your upper body.
If you're not careful, the former machine may put you in a position to crank your neck unpleasantly. Avoid doing that. Controlling your neck keeps this from happening.
The latter machine involves no potential neck cranking, but it might feel awkward if you've never used one.
Aside from that, look at the machine to see if there are ways to adjust it for your body type. After that, press your back up against the seat, and perform the exercise. Start lighter than you need to, and adjust the weight accordingly.
Cable Crunches
This variant is similar to the machines, only you're not seated, nor do the constraints of the machine itself bind you. You have significantly more freedom to position yourself most optimally.
First, grab a yoga mat or something to pad your knees.
Next, attach the rope handle to the top pulley on the cable machine. This is the same rope many people use for tricep extensions.
Third, bring that rope to your forehead, and kneel on your padding. Keep the knee joint at 90 degrees or close to it. If the angle is too low, you won't get nearly the same intensity of your ab contraction.
Fourth, bring your chin to your chest to flex your abs, and repeat often.
Keep your hips in place and maintain the integrity of the knee joint angle to further make the most of this exercise.
Side Bends
Side bends, or side crunches, target the obliques and your lateral flexion and extension. They also aren't difficult to perform.
To perform, stand straight and look forward. Keep your feet roughly shoulder-width apart.
Laterally flex your spine by sliding your hand along your leg toward the knee.
Reverse the motion and stand straight.
One of the more common errors with the side bend is holding a dumbbell or kettlebell in each hand. To properly move against the resistance, hold one weight in either hand. Whichever side holds the weight is where you flex. For instance, if you're holding a weight in your left hand, the left side of the torso is laterally flexing for this exercise.
If you hold two weights, you're merely counterbalancing yourself like a teeter-totter and not providing any substantial work on your musculature.
Leg Raises
If you have a bar to hang from, do hanging leg raises. Not only are they effective, they're easy to scale to your abilities. Can't hang from a bar? Use the dip station at the gym with the arm pads. Can't do that? Lie flat on your back.
You do the basic leg raise while hanging from a bar. To perform it, hang from the bar, tighten your core, and keep your body straight.
Next, lift your knees as if you're trying to touch them to your face. Like in the reverse crunch, your lower back flexes, working your abs and psoas.
That description explains an easier variation which is typically called a knee raise. To make it more difficult, gradually straighten your legs over time.
Another simple variation is lying flat on the floor, performing a reverse crunch, and gradually straightening your legs over time.
Myths And Realities: Spot Reduction
One of the biggest myths of all is that of spot reduction. Spot reduction targets a given area of the anatomy via exercise with the belief that it reduces your adipose tissue in that area.
If you believe the marketing in the late-night infomercials for the ab machines, it's not a hard leap of logic to make — especially since the people in the commercials seem so confident and super toned.
But the American Council on Exercise concisely explains: "Exercises such as crunches or leg lifts improve the tone and endurance of the muscles, but they don’t burn fat."
Indeed, they do not. Body fat has a different function than muscle tissue; therefore, the processes that guide it differ. With muscle protein synthesis, there is a catabolic and anabolic effect that happens during the workout and after the workout, respectively. Muscle protein synthesis builds the muscle; exercising breaks it down. Given the many available exercises, you choose which muscles to build and which to neglect.
Hypertrophy is possible on a given spot, but fat loss isn't since you burn the excess energy you have from your body fat reserves.
So, doing crunches to lose fat isn't going to work. However, eating in a caloric deficit while following good food behaviors accomplishes will help you lose fat.
Hypertrophy: Spot Addition
You've read it several times here, but it's worth repeating: Abs are muscles. Since they are muscles, they are no different from your biceps or quads in terms of metabolic processes.
This means that they are susceptible to hypertrophy. If you've never done a single ab workout in your life, the hypertrophy might be noticeable quickly.
Depending on your head space, having a physically bigger stomach, whether the tissue is fat or muscle, wreaks havoc on your body image, or it might be a sort of muscle gain you never knew you wanted. The other side of that coin is that they'll be stronger.
Abdominal hypertrophy is possible, and only you know your mental state. If your diet is in check, then getting bigger abs isn't something you'll need to worry about: It's simply a possibility in the interest of awareness.
Reps, Sets, And Frequency
If you've paid attention thus far, you've learned that the abs do a lot. Think about it. They keep your spine stable when you perform a barbell squat. If they didn't do so, you'd fold over under a barbell, at best risking embarrassment at the gym or, worse, irreparably hurting yourself.
The same holds for a deadlift. Without the abdominal pressure, your spine would bend, and eventually, you might lift the bar off the ground, but it would be in the least advantageous way possible. Again, you'd look foolish at best; the worst-case scenario would be a severe injury.
Now, think about all the other exercises you perform. See if you can parse out what your abs might be doing during those exercises. Chances are, they're likely keeping your spine stable. Think about your pull-ups, planks, and lat pull-downs.
Your abs get quite a lot of work that way. The downside is those exercises don't train spinal flexion, and few actively train the psoas muscle against any resistance.
Incorporating ab movements, like crunches, two or three times a week, depending on your workout program, aids in training the seldom-used motions of the spine and all the stability work they get from your other exercises.
The other benefit is that your abs handle much volume because of how much work they do.
When you make it a point to train your abs directly, err on a little more intensity by using some of the crunch modifications here by your ability.
Applying It All
The best way to add ab workouts to your exercise program is to see what movements you lack. Typically, flexing movements, like crunches, may be missing from your program, and lateral flexing, like the side bends.
From there, add in some crunches. Pick the variations you like, dial up the intensity to where you need it for a good challenge, and see how your overall fitness improves over time.
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