Dumbbell Fly vs Bench Press: What the Research Shows

The bench press and the dumbbell fly both train the chest, but they are not rivals in the way most comparison articles suggest. In the one study that put them side by side, the bench press produced more muscle activity in the chest, front shoulder and triceps. The fly produced more in the biceps. That is a measurement of effort in one session, not of growth.

We could not find a long-term trial that compared the two for chest size or strength. So this article reports what was measured, says where we are reasoning beyond the data, and shows how to keep a record that lets you judge the fly in your own training.

Is the dumbbell fly or the bench press better for chest?

The research does not crown either. The bench press produced more activity in the main chest and pressing muscles, and it lets you load the movement far more heavily. The fly has no direct growth comparison. A reasonable reading is that the press is the base of a chest session and the fly is an optional add-on.

That is a judgement, and it rests on thin evidence. Solstad et al. measured muscle activity, and Pinto et al. studied a machine fly without a bench press group. If you want the wider picture on exercise roles, our how to build chest muscle guide covers weekly sets, exercise selection and progression for the whole chest.

What do EMG studies show about the fly and the bench press?

Surface electromyography (EMG) records electrical activity in a muscle during a lift. In the only direct comparison we found, the barbell bench press led for the chest, front shoulder and triceps, while the dumbbell fly led for the biceps. EMG shows how active a muscle was, not how much it will grow.

Solstad et al. (2020) tested 17 resistance-trained men with about 4.8 years of lifting experience. EMG was recorded from the pectoralis major, anterior deltoid, triceps brachii and biceps brachii during six-repetition-maximum (6RM) sets of each lift. The results:

The authors concluded that both lifts could go in a program, but that the bench press should be emphasised because of its higher overall muscle activation. They added that where tasks need strength and control in a horizontal shoulder flexion position with extended elbows, the fly might be useful for some populations.

Two cautions apply. The sample was 17 trained men, so the result may not carry over neatly to women, beginners or older lifters. And both lifts were done at a 6RM, a heavy load that most people would not use for flys. We do not know whether the pattern holds at 12 to 15 reps.

Welsch, Bird and Mayhew (2005) looked at three lifts in 12 college-age men and women: barbell bench press, dumbbell bench press and dumbbell fly. Activation of the pectoralis major and anterior deltoid did not differ significantly across the three, and the fly had a shorter relative time of activation than either press. The authors suggested the fly for an auxiliary role and said the presses could be used interchangeably. Our dumbbell vs barbell bench press article covers that comparison in detail.

Does a fly-type exercise build chest muscle?

Yes, in the study we found, a fly-type machine grew the chest in untrained men. That shows the movement can work for beginners, but it does not show the fly beats or matches the bench press, because there was no press comparison group.

Pinto et al. (2025) had 15 untrained young men train the pec deck for 12 weeks. A within-subject design meant each person trained under both the one-set and three-set conditions, taking sets to failure in a linear periodised scheme running from 20RM down to 8RM. Ultrasound measured muscle thickness, and the results were:

The authors found no effect of volume and no evidence of regional growth in the upper or lower chest from this exercise. For the reader, three points matter:

• Untrained participants. Beginners tend to respond to almost anything. The result is a weak guide for someone with years of pressing behind them.
• A machine, not a dumbbell. The pec deck is a fly-type movement, but we cannot assume the same numbers for free dumbbells.
• One set matched three. That is a useful time-saving hint for beginners. It does not tell a trained lifter that one set of flys is enough.

Does the stretch in a fly matter for growth?

Possibly, but the evidence we found is indirect. One 8-week trial showed that pectoral stretching alone can raise muscle thickness, and a lengthened position is a common reason to include flys. No study we found tested the fly against the bench press on this idea.

Wohlann et al. (2024) split 81 active participants into a stretching group, a resistance training group and a control group. Stretching of the pectoralis major ran 15 minutes a day, four days a week. The training group did five sets of 12 reps, three days a week. After eight weeks, strength and muscle thickness gains were comparable between stretching and resistance training. The authors noted that the equipment and long durations needed make this impractical outside special circumstances.

What we take from it, and this is our reading, is that tension on the pec at a long length seems to be a real stimulus. It is not proof that the fly's bottom position produces more growth than a deep bench press. If you want to follow the range-of-motion question further, see full range of motion vs partial reps.

Where does the fly fit in your training week?

Put it after your main press and treat it as an add-on. This is our suggestion rather than a studied protocol, but it matches the studies: the press gets the heavy, high-activation work, and the fly gets lighter loads and higher reps where the load is not limited by your triceps or shoulders.

A simple way to set it up:

1. Press first. One flat or incline press as the heavy lift, with a rep range and a target effort you can repeat.
2. Fly second. One to three sets, in a rep range such as 10 to 15, stopping with 1 to 3 reps in reserve (RIR).
3. Progress with double progression. Keep the same dumbbells until every set reaches the top of the range, then step up to the next pair. Dumbbell jumps can be large, so progress may be slow and that is normal.
4. Review after a block. After four to six weeks, look at whether the fly sets got heavier or smoother. If they did not, the slot may be better used on an extra press set.

None of this means you need the fly. If your session is short, a second pressing variation is a simpler choice and carries over to a heavier lift.

Dumbbell fly, cable fly or pec deck: does the version matter?

We found no head-to-head trial comparing these versions for chest growth, so the choice is practical. Pinto et al. used a pec deck. Solstad et al. used dumbbells. Neither tested cables. Equipment, comfort and how well you can progress the load should decide it.

The points below are our reasoning, not study findings:

Haugen et al. (2023) pooled studies of free weights against machines and found no difference in muscle growth. That was a general comparison, not about flys, so treat it as background. Our free weights vs machines article covers it in full.

How do you log fly and bench press work in IronLedger?

Log them as separate exercises so each keeps its own history, and record RPE or RIR on every set. IronLedger stores weight, reps, RPE or RIR and a note for each set, so a fly that feels hard at 12 kg is not confused with a press that feels easy at 80 kg.

A practical approach:

• Pick one dumbbell convention. IronLedger does not have a per-hand weight setting that we know of, so write "weight is per hand" in the set note on your first fly and stick with it.
• Use RIR for the fly. Reps in reserve is easier to judge on an isolation lift than a percentage of a max. Our RPE vs RIR guide explains both scales, and the RPE calculator helps convert between them.
• Track the press with estimated 1RM. The progress view records personal records and an Epley estimated 1RM for each lift, plus per-lift trends. Use it for the bench press, not for the fly, where a one-rep max is a poor guide.
• Look at the whole history. Because history has no cutoff, you can compare a block with fly sets to an earlier block without them and see whether your pressing numbers moved. That shows association in your own training, not cause.

What mistakes should you avoid when choosing between them?

• Treating EMG as a growth result. Higher activation in one session does not show more muscle gained over months.
• Using the fly as the main chest lift. Welsch et al. suggested an auxiliary role, and Solstad et al. recommended emphasising the press.
• Dropping the fly because one study found lower activation. The study used a 6RM and measured one session. It does not say the fly does nothing.
• Reading the pec deck result as a bench press result. Pinto et al. had no press group and tested untrained men.
• Changing everything at once. Swap one thing per block, so your log shows what changed.
• Chasing heavier dumbbells at the cost of range. A heavier pair with a shorter movement is not progress. Compare like with like.
• Ignoring pain. If a fly hurts your shoulder, stop and speak to a qualified clinician rather than pushing through.

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