Crunches are great for building abs but less awesome for supporting swim performance. Here’s what to focus on instead.
Core training is one of the best forms of dryland for competitive swimmers.
A stronger, more stable trunk supports a lot of things swimmers love: faster swimming speeds, improved turn times, and better body position in the water.
When choosing the best core exercises for faster swimming, swimmers and coaches usually land on the standard, the classic, the ab exercise that started it all—the crunch.
While great for working the ab muscles, the classic crunch shouldn’t be the first core exercise that swimmers reach for.
Here’s why.
The Limitations of Crunches for Swimmers
The problem with crunches isn’t that they aren’t fantastic for developing the six-pack—they can definitely do that—but how they work them.
For swimmers, crunches:
Adds compression you don’t need.
Your basic crunch loads the spine with roughly 2,000 N of compression (McGill and Axler, 1997). Swimming is one of the few sports where we actively unload the spine.
This spinal compression alone makes it worth asking why you’d spend valuable training time re-loading it in flexion when other exercises build the same strength without the spinal squeeze.
Over-indexes on one muscle.
The trunk works best when it works as a system. Crunches hammer the rectus abdominis (the “six-pack”) like an absolute boss, but other critical core muscles like the internal and obliques barely flicker in terms of activation.
Swimmers deeply rely on anti-extension and anti-rotation to control the body when swimming, and over-developing the RA helps little in building these qualities.
Trains the wrong body shape
Every crunchy-crunch curls and squeezes the trunk in a short and tight position. This action shortens the distance between the rib cage and the pelvis—the exact opposite of the long, tall, and rigid line a swimmer needs to move cleanly through the water.
Anti-movement exercises are better (and safer)
Fast performances in the water require the core to transfer force from the hips to the hands while resisting the stroke’s rotation and undulating forces. These are anti-movement tasks—bracing the trunk against unwanted motion—way more than a trunk curling one.
This is why a high-performance core training program is built around anti-movement exercises like planks, dead bugs, Pallof presses, and isometric holds.
A study (Cinarli et al., 2025) compared anti-movement exercises like planks and bird dogs against dynamic core exercises—crunches, leg swings—and found that the anti-movement improved core efficiency much better.
Less transfer
The real issue with crunches—and dryland training in general—is whether it translates into better performance. Core training is done to support faster swimming. That’s the goal, that is why we do it. (The nice abs in the mirror part is obviously a nice side benefit.)
But core training interventions are not a guarantee for improving performance. A meta-analysis (Prieske et al., 2016) showed that core training programs were great for improving core strength. But there were only modest improvements in performance.
The bottleneck isn’t how much core training you do, but doing the kind of exercises that transfers and lands into your swimming.
A movement like the crunch builds strength in a curled pattern your body almost never uses in the water, so much of that gain never shows up on race day.
How to Program Crunches for Swimmers
So does this all mean that crunches should get thrown into the gutter?
Not necessarily.
While the utility of the crunch for swimmers isn’t the best, they can still be a part of a complete core training program that covers all of the essentials.
Start by:
Focusing on the movements that move you in the water
The goal with core training is to support your swimming. Prioritize core exercises that give you the body position, roll control, and force transfer that lead to faster swimming.
- Anti-rotation exercises – Pallof presses
- Anti-extension – Planks, Dead bugs, bird dogs
- Anti-lateral flexion – Suitcase carries, Farmer’s walks
Once you have the main stuff in your program, feel free to add the crunch in an accessory role.
Keep the volume sane
Crunches can be easy to belt out in high reps. Swimmers often use them as “finishers”—cranking them out until failure. Instead of doing hundreds of sloppy crunches, start with sets of like 2×15, building tolerance and lumbar-flexion strength.
Even better, use a stability ball to increase range, support the back, and roughly double muscle activation compared to a floor-based crunch (Sternlicht et al., 2007).
Avoid if you have back issues
Spinal flexion exercises like crunches and sit-ups generate high compressive force on the spine. Repeated flexion can stress discs over time—further aggravating existing back pain.
(Lower back pain is incredible common in swimmers, particularly butterflyers and breaststrokers.)
You can still get an excellent core workout without the crunching—isometric exercises like planks, bird dogs, and dead bugs work the core while keeping the spine in a fixed position.
Save crunches for afternoon workouts.
This one is important for those early morning swim workouts. The discs in your back absorb fluid overnight and are most swollen, stiff, and vulnerable right after you wake up.
A review (Contreras & Schoenfeld, 2011) of crunch studies recommends avoiding spinal flexion within 1-2 hours of rising.
If you’re doing core before a 5am swim practice, that’s a legitimate reason to push this type of ab work later in the day, or at least move around and warm up first.
Respect the recovery window.
Daily crunches aren’t a good idea for two reasons.
First, the muscle-protein-synthesis response to training runs around 48 hours, and hitting the same muscle group hard can blunt development.
And second, and more specific to the crunch, the discs in the back have poor blood supply, so they take even longer to recover compared to muscle. Contreras & Schoenfeld (2011) recommend a minimum of 48 hours between dedicated flexion training.
The Bottom Line
Crunches aren’t necessarily a bad exercise, and when it comes to hitting the six-pack muscles, they are very effective.
They’re just not great for what we are trying to accomplish in the water. If your goal is getting faster, build your core training around the things it does in the water.
It should be centered on:
Holding bodyline. Resisting movement. Transferring force.
Once those boxes are checked, crunches can earn a supporting role, but they shouldn’t be the star of the show.
