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Chest

Pec Deck

The Pec Deck is a strength exercise on a machine for your chest. Share of the load in the Zulta muscle model: mid chest 49%, upper chest 17% and lower chest 15%.

Also known as: butterfly, butterfly machine, machine fly, pec dec, seated machine fly

Level: BeginnerEquipment: MachineSingle-joint (isolation)

How to do it

  1. Set the seat so the handles are at mid chest height and set the arms so you feel a light stretch at the start.
  2. Sit tall with your back against the pad and feet flat on the floor.
  3. Grab the handles with the arms open wide and the elbows slightly bent.
  4. Bring the handles together in front of your chest in a smooth arc.
  5. Let them open slowly until your hands are in line with your shoulders.

Tips

  • Keep your chest up and shoulder blades back against the pad.
  • Squeeze for a second where the handles meet.

Common mistakes

  • Letting the shoulders roll forward as the handles close.
  • Letting the weight pull the arms far behind the body.
  • Jerking the handles together with momentum.

Muscles worked by the Pec Deck

  • Mid chest Primary49%
  • Upper chest Secondary17%
  • Lower chest Primary15%
  • Front delts Secondary11%
  • Biceps (short head) Minor4%
  • Serratus anterior Stabilizer4%

Share per muscle in the Zulta muscle model. The model spreads the load of one rep over 40 muscles, based on EMG and biomechanics research.

Fixed arc, seated, little stabilising. A fly is pure shoulder horizontal adduction with the elbow fixed, so the pec does nearly all the work and the triceps drop out.

Pec Deck alternatives

Same equipment

Different equipment

Make it harder

Similar exercises

Frequently asked questions

What muscles does the Pec Deck work?

Mainly the mid chest and lower chest. The upper chest and front delts assist.

Is the Pec Deck good for beginners?

Yes. The Pec Deck is rated beginner in the Zulta library: the technique is easy to learn with a light weight.

What is a good alternative to the Pec Deck?

For example the Band Fly, Cable Fly and Dumbbell Fly. They train mostly the same muscles, some with different equipment.

How do you make the Pec Deck harder?

Add weight or reps, or move on to the Flat Bench Cable Fly and TRX Chest Fly.

Sources

  • Welsch et al. 2005, JSCR 19(2):449-452 (bench, incline, fly)
  • Solstad et al. 2020, J Sports Sci Med 19(4):645-651 (bench press vs fly)

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Zulta tracks your sets, weights and muscle load next to your running, riding or Hyrox training. The app opens soon.

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