You’ve seen that guy. The one at the gym hogging a flat bench, not with a massive barbell, but with a single, lonely dumbbell. He looks slightly off-balance. He’s grunting more than usual. You might think he’s just trying to be different or that he couldn't find the matching pair of weights. Honestly? He might actually be the smartest person in the weight room.
The one arm db chest press—or the single-arm dumbbell bench press if you want to be formal—is one of those moves that looks simple but feels like a total trap once you actually lie down and try it. It’s not just a chest exercise. It’s a full-body stability test that exposes every weakness you’ve been hiding behind a standard barbell. If your core is weak, you’ll roll off the bench. If your shoulder stability is trash, the weight will wobble like a Jello mold.
Most people treat the bench press as the ultimate measure of strength. We get it. Pushing heavy iron is fun. But the barbell is a liar. It allows your dominant side to take over, masking imbalances that eventually lead to rotator cuff tears or "weightlifter's shoulder." Switching to a unilateral (one-sided) movement changes the physics entirely.
Why Your Core Hates (And Needs) the One Arm DB Chest Press
Physics is a jerk. When you hold a heavy dumbbell in your right hand and nothing in your left, your body becomes a see-saw. The weight wants to pull your right shoulder toward the floor and flip your entire torso off the side of the bench. This is called "anti-rotational" force. To stay flat and stable, your left obliques, your glutes, and your deep spinal stabilizers have to fire like crazy.
Dr. Stuart McGill, a world-renowned spine biomechanics expert, has frequently discussed how unilateral loading creates massive "stiffness" in the core. It’s functional. Think about life. When do you ever push something with both hands perfectly symmetrical? You’re usually pushing a door open with one hand, carrying groceries with another, or lunging to catch a falling kid. The one arm db chest press trains your body to produce power from an unstable, asymmetrical base.
It’s a secret core workout. If you do these right, your abs will probably be more sore the next day than your pecs. That’s not a bug; it’s a feature. You’re teaching your nervous system to "cross-pollinate" strength from your hips up through your torso and out through your arm.
Fixing the "Stanky" Shoulder
Let’s talk about shoulder health. The barbell bench press locks your hands into a fixed position. Your wrists can't move, your elbows are forced into a specific path, and your shoulder blades are pinned. For a lot of guys, this is a recipe for impingement.
The dumbbell allows for "natural" rotation. As you lower the weight during a one arm db chest press, your palm can naturally rotate from a prone position to a neutral position (hammer grip). This opens up the subacromial space in your shoulder. It lets the joint breathe.
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Moreover, because you only have one weight to worry about, your brain can focus entirely on the "packing" of that one shoulder blade. You aren't splitting your attention. You can feel the lat engage. You can feel the serratus anterior—that finger-like muscle on your ribs—working to stabilize the scapula. This is why physical therapists often use single-arm presses for athletes coming back from labrum or rotator cuff issues. It builds "bulletproof" shoulders by forcing the small stabilizer muscles to do their job instead of letting the big, dumb pecs do all the work.
The Setup: Don't Fall Off
- Sit on the edge of the bench with one dumbbell resting on your thigh.
- Kick the weight up as you lie back. Keep your feet wide. Seriously, wider than you think.
- Your non-working hand shouldn't be grabbing the bench for dear life. Hold it out to the side or clench your fist over your chest to create "irradiation"—a fancy word for full-body tension.
- Drive your heels into the ground. Your glutes should be tight.
- Lower the weight slowly. Don't let it pull your shoulder into the bench. Control the descent.
- Press back up, exhaling sharply.
The Myth of "Less Weight, Less Gains"
The biggest ego-crusher with the one arm db chest press is the weight. You won't be able to press half of what you do with two dumbbells. If you can press 80-pounders for sets of 10, don't expect to waltz in and do 80 pounds with one arm. You’ll likely struggle with 60.
People think this means they are getting weaker. They’re wrong. You’re actually recruiting more motor units because the brain has to work harder to balance the load. There is something called the "bilateral deficit." Interestingly, some studies suggest that the sum of your unilateral strength is actually higher than your bilateral strength. Basically, your body can focus more "juice" into one limb when it doesn't have to worry about the other.
Over time, this leads to a higher ceiling for your standard bench press. You’re clearing out the "weak links" in the chain. When you go back to the barbell, you’ll find you’re more stable, your "groove" is tighter, and those nagging shoulder pains have mysteriously vanished.
Common Mistakes That Make You Look Silly
We see it all the time. People try to "cheat" the rotation by twisting their hips. If your butt leaves the bench or your opposite hip lifts up, you've failed the rep. The goal is to keep your torso as still as a statue. If you have to drop the weight by 20 pounds to keep your hips flat, do it. Nobody cares how much you’re pressing if you look like a fish flopping on a boat deck.
Another big one: the "death grip" on the bench. If you use your free hand to hold onto the side of the bench, you’re negating the core benefits. You're using the bench as a crutch instead of your obliques. Keep that hand free. Experience the wobble. Own the wobble.
Range of motion matters too. Since there's no bar to hit your chest, people often cut the rep short. Or worse, they let the dumbbell sink way too deep, stretching the front of the shoulder into a vulnerable position. Stop when your elbow is just slightly below the bench height. That’s the sweet spot for pec activation without wrecking your joints.
Programming for Progress
Don't make this your primary "heavy" lift of the day. It’s better suited as a "second" movement. Do your heavy squats or rows first, then move into the one arm db chest press for higher volume.
- For Stability: 3 sets of 12-15 reps. Focus on a 3-second descent.
- For Strength: 4 sets of 6-8 reps. Go as heavy as you can while keeping your hips glued to the bench.
- The "Finisher": Try a single-arm press on a Swiss ball if you really want to hate your life. (Actually, don't do that until you've mastered the flat bench version—it's dangerous for beginners).
Real-World Benefits
Think about a football player (American or otherwise). They are rarely pushing an opponent with both hands in a perfect line. Usually, they are shedding a blocker with one arm while reaching for the ball carrier with the other. A fighter throwing a punch is the ultimate expression of unilateral power—driving from the foot, through the core, and out one arm.
The one arm db chest press is essentially a "punching" movement performed while lying down. It builds that cross-body power (the functional line from the right hip to the left shoulder) that is essential for almost every sport. If you’re a golfer, a tennis player, or even a weekend warrior who plays pickup basketball, this move will do more for your game than a 315-pound barbell bench ever will.
Action Steps to Start Today
If you’re ready to stop being a "symmetrical-only" lifter, here is how you integrate this into your next chest or upper-body day.
First, swap your second chest exercise (like the incline fly or cable cross-over) for the single-arm press. Start with a weight that is roughly 30% lighter than what you would use for standard dumbbell presses. If you usually use 50s, grab a 35.
Perform your sets on your "weak" side first. Usually, this is the left arm for right-handed people. Match the reps with your strong side. If your left arm gasses out at 8 reps, don't do 12 with your right just because you can. This is how you actually fix the imbalance.
Focus on your feet. Dig your toes into your shoes. Feel the tension in your quads. The one arm db chest press is a full-body contraction. If you're relaxed from the waist down, the weight will win. Be the hammer, not the nail.
Lastly, track your progress not just by the weight on the dumbbell, but by the "quietness" of your body. When you can press a heavy weight without a single twitch in your hips or a wobble in your wrist, you’ve officially mastered the movement. You’ll likely find that your "big" lifts start moving up shortly after. Strength is a skill, and unilateral training is the best way to sharpen it.