Dumbbell Flyes

What it trains. The fly is a single-joint exercise. The shoulders bring the upper arms across the body (horizontal adduction) while the elbows stay fixed at a slight bend. Keeping the elbows still is what separates a fly from a press.

• Primary: pectoralis major, sternal (middle and lower) fibres most, clavicular (upper) fibres too.
• Secondary: anterior deltoid (front shoulder) and biceps brachii, which helps hold the arm and the fixed elbow.
• Stabiliser: serratus anterior and pectoralis minor steady the shoulder blades.

Why it feels so much harder than a press. With the arms out wide, the weight sits far from the shoulder, so the same dumbbell creates much more turning force (torque) at the joint than in a press. The triceps can't help either, because the elbows don't straighten. That's why you fly with far lighter weights than you press.

How it compares with the bench press.

• Solstad et al. (2020) tested 17 trained men at a 6-repetition maximum. The barbell bench press produced higher overall chest activity (about 16%) and front-shoulder activity (25%) than the dumbbell fly. Biceps activity was 57–86% higher in the fly.
• Welsch, Bird & Mayhew (2005) found similar chest and front-shoulder activation in the fly and the presses, but the chest was active for less of each rep in the fly. Their conclusion: use the fly as an auxiliary lift beside a press.

So the press should stay your main chest lift. The fly adds chest work without loading the triceps or elbows the way a press does.

Flyes build size, not "shape". Older training advice said presses build chest mass and flyes build shape. Research doesn't back that split:

• A muscle's shape is set by its anatomy; training makes it bigger, not a different shape.
• In Pinto et al. (2025), 15 untrained men trained only the pec deck (a machine fly) for 12 weeks. Chest muscle thickness grew 17–18% in the upper (clavicular) portion and 21% in the middle (sternocostal) portion, with no regional difference. One set gave the same growth as three in these beginners.
• So a fly is a real chest builder, not a finishing touch for "definition".

Dumbbell, cable or machine.

• Dumbbells load the chest hardest at the bottom, where the arms are wide and the lever is longest. Tension drops near the top as the weights line up over the shoulders.
• Cables (Cross Over Cables) keep tension on through the whole arc, including where the hands come together.
• Pec deck (Pec Deck) fixes the path, which makes it the easiest version to learn and to take close to failure safely.

ACSM 2026 found that equipment type didn't consistently change training outcomes, so choose the version that feels best on your shoulders and fits your gym.

Technique cues (dumbbell):

• Lie on a flat bench, dumbbells above your chest, palms facing each other, elbows slightly bent. Keep that bend the same for the whole set.
• Settle your shoulder blades back and down on the bench.
• Lower the dumbbells out to your sides in a wide arc until you feel a stretch across your chest. Stop where you can still control it; don't let the weights drop below where your shoulders feel comfortable.
• Bring them back up along the same arc, as if hugging a large tree.
• Don't bend and straighten the elbows. That turns the fly into a press.
• Start much lighter than you press, and add weight only while the elbow angle and the arc stay the same.

See it. Demo clips in the Fysiqal media library: Dumbbell Flye, Cable Crossover, Pec Deck.

• Lifters who want extra chest volume without more triceps and elbow work than their pressing already gives.
• People whose elbows or wrists limit heavy pressing.
• Beginners on a machine: the pec deck grew the chest well in untrained men (Pinto 2025).

• Healthy shoulders only. The stretched bottom position is where the shoulder is most exposed. With current shoulder or chest pain, a recent dislocation or a pec injury, get individual advice first.
• Not a press replacement. The bench press produced more chest activity per rep than the fly (Solstad 2020). Use the fly beside a press, not instead of it, if strength is the goal.
• Small studies. Solstad 2020 had 17 men, Welsch 2005 had 12 people, and Pinto 2025 had 15 untrained men. Muscle-activity (EMG) studies show how hard a muscle works in a rep, not how much it will grow.
• Beginners vs trained lifters. One set matching three sets (Pinto 2025) applies to untrained men; trained lifters usually need more weekly sets (see Weekly Sets per Muscle).

Priya presses 2 × 20 kg dumbbells for 8 reps and wants more chest work without more elbow strain.

1. Choose a version. Her gym has a pec deck, so she starts there because the path is fixed and she can push sets hard without balancing weights.
2. Plan for 8 weeks, twice a week, after her presses:
   • Pec deck, 2 × 12–15, stopping 1–2 reps short of failure.
   • When she reaches 15 reps on both sets, she adds the next weight on the stack.
3. Range check. At first she lets the handles go back as far as the machine allows, and the front of her right shoulder aches. She sets the start so the handles stop where she feels a firm stretch but no pinch.
4. Result: the ache goes, her pec deck load rises from 25 to 35 kg, and her pressing keeps progressing.

Next lesson: Farmer's Carry. Add a loaded carry to train grip and a braced trunk while walking.

• Primary: pectoralis major. Secondary: anterior deltoid and biceps brachii. Serratus anterior stabilises the shoulder blades. Joint action: shoulder horizontal adduction with a fixed elbow.
• The barbell bench press produced about 16% more chest activity and 25% more front-shoulder activity than the dumbbell fly; biceps activity was 57–86% higher in the fly (Solstad 2020).
• The chest was active for less of each rep in the fly than in the barbell or dumbbell press (Welsch 2005).
• Pec deck training alone grew chest thickness 17–21% in 12 weeks, with no regional difference and the same growth from 1 or 3 sets in untrained men (Pinto 2025).
• Equipment type didn't consistently change training outcomes (ACSM 2026).
• Use far less weight than you press, and lower only to a stretch you can control.