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  3. Exercises
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  5. Chest
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  7. Dumbbell One Arm Bench Fly

Exercise guide

Dumbbell One Arm Bench Fly

  • Intermediate
  • Isolation
  • Rep-based
  • Chest
  • Shoulders

This unilateral isolation exercise targets the pectoralis major and anterior deltoids while significantly challenging core stability to prevent torso rotation. It allows for a greater focus on mind-muscle connection and helps correct muscular imbalances between the left and right sides.

Reviewed by the Crucible Fit team · Updated June 2026

Watch the Dumbbell One Arm Bench Fly demonstrationVideo and instructions for every movement are in the Crucible Fit app.

Muscles worked

Primary

  • Pectorals

Secondary

  • Triceps

Equipment

  • Dumbbell

Setup

  1. Sit on the end of a flat bench with a dumbbell resting on your thigh.
  2. Lie back on the bench, plant your feet wide on the floor for stability, and press the dumbbell directly over your chest.
  3. Place your non-working hand on your hip or grip the side of the bench to help stabilize your torso against the off-center load.
  4. Retract your shoulder blades into the bench and maintain a slight, natural arch in your lower back.

How to do it

  1. Inhale as you slowly lower the dumbbell out to the side in a wide arc, keeping a slight, fixed bend in your elbow.
  2. Lower the weight until your upper arm is parallel to the floor or you feel a deep, comfortable stretch in your chest.
  3. Exhale as you reverse the movement, squeezing your chest to bring the dumbbell back to the starting position over your midline.
  4. Maintain a controlled 3-second lowering phase and a 1-second squeeze at the top.

Form checklist

  • Keep your wrist neutral and firm; do not let it bend backward.
  • Ensure your hips and shoulders remain square to the bench; do not let the weight rotate your body.
  • Maintain a consistent 10-15 degree bend in the elbow to protect the joint.
  • Stop the upward motion just before the dumbbell is directly over your shoulder to keep constant tension on the pec.

Pro tips

  • Focus on driving your inner bicep toward your sternum at the top of the movement to maximize the peak contraction.
  • Actively brace your core and press the opposite foot into the floor to counteract the rotational force of the dumbbell.
  • Imagine hugging a large barrel to maintain the correct arm arc throughout the set.

Make it harder

  • Add a 2-second pause at the bottom of the rep to emphasize the loaded stretch phase.
  • Bring your feet closer together or lift them slightly off the floor to further challenge your core's ability to resist rotation.

Frequently asked

What muscles does the dumbbell one arm bench fly work?
The dumbbell one arm bench fly primarily targets the pectorals, and also works the triceps as secondary muscles.
What equipment do you need for the dumbbell one arm bench fly?
The dumbbell one arm bench fly uses dumbbell.
Is the dumbbell one arm bench fly good for beginners?
The dumbbell one arm bench fly is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.

Related exercises

  • Air Punches MarchBeginner · calves, pectorals, and quadriceps
  • Alternate Front Kick In Place With Arm CirclesBeginner · abs, calves, deltoids, and pectorals
  • Archer Push-UpAdvanced · pectorals
  • Arm CrossoverIntermediate · deltoids and pectorals

Train it with Crucible Fit.

Every movement in this library is in the app with video and instructions, ready for your own sessions on the days between Crucibles. Your first Crucible is on us.

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