Dumbbell Flies Match Bench Presses for Chest Muscle Growth: New Study Busts Gym Myth

Key Takeaways of Dumbbell Flies Match Bench Presses for Chest Muscle Growth

• No Significant Differences: When it comes to chest muscle growth, dumbbell presses and dumbbell flies produced statistically similar gains across medial, intermediate, and lateral pectoral regions.

• Total Thickness Increases: Dumbbell presses expanded summed pectoral thickness by 13.1%, while dumbbell flies produced a 14.6% increase.

• Effort Dictates Results: Both movements stimulated substantial growth because participants trained with progressive overload and pushed sets to high exertion levels.

• Neither Movement Proved Superior: The findings show flies serve as a viable alternative, not a superior replacement.

  ---

Chest Muscle Growth: Is the Bench Press Essential?

Many bodybuilders insist that multi-joint compound presses are essential for pectoral hypertrophy. They argue that heavy barbell loading creates unique hormonal and mechanical stimuli. Consequently, athletes often view isolation movements like dumbbell flies as minor accessory exercises.

Biomechanical researchers previously hypothesized that dumbbell flies might actually stimulate greater growth than presses (Dell’Avanzi et al., n.d.). They reasoned that flies maintain a longer resistance moment arm when the pectorals reach a stretched position. However, prior investigations relied primarily on acute muscle activation rather than long-term growth measurements. This trial directly tested whether those movement differences alter real muscle growth over time.

Study Design: Comparing Two Exercises for Chest Growth

The researchers recruited 46 healthy, resistance-trained men between 18 and 35 years of age. After testing, participants were counterbalanced into two training groups:

• Dumbbell Bench Press: Combined shoulder horizontal adduction with active elbow bending and straightening.

• Dumbbell Fly: Performed shoulder horizontal adduction while maintaining a constant slight bend at the elbows.

Participants completed two weeks of familiarization followed by ten weeks of supervised training twice weekly. Furthermore, coaches individualized volume based on each participant’s prior habits, resulting in an average of 14 weekly sets for presses and 13 weekly sets for flies.

Lifters performed 8 to 12 repetitions per set using a controlled tempo of one second lifting and two seconds lowering. Each lifter maintained approximately two repetitions in reserve on initial sets, but pushed the final set of each session to concentric failure.

A blinded technician measured muscle thickness using ultrasound at three anatomical locations: medial (30%), intermediate (50%), and lateral (70%). In addition, testing occurred at least 72 hours after the final session to reduce the influence of acute muscle swelling.

Chest Muscle Growth Results at Three Measurement Sites

At the end of ten weeks, both movements triggered clear chest muscle growth across all measured regions.

As displayed in the ultrasound data, neither movement demonstrated a statistically significant advantage over the other at any individual region or for total summed thickness.

Moreover, working loads differed significantly between protocols: the press group lifted 27 ± 5 kg (59 ± 11 lb) while the fly group used 20 ± 8 kg (44 ± 18 lb). Nevertheless, the lighter fly loads produced equivalent tissue expansion.

Critical Study Limitations You Should Know

Although these outcomes challenge dogma, lifters must interpret them with appropriate caution:

1. High Dropout Rate: Twenty of the initial 46 lifters discontinued the study, leaving only 13 completers per group for final statistical analysis.

2. Thickness vs. Volume: Ultrasound measured muscle thickness at three specific points along a horizontal line rather than whole-muscle three-dimensional volume via magnetic resonance imaging.

3. Upper Chest Missing: The investigators did not measure the clavicular head of the pectoralis major.

4. Uncontrolled Nutrition: Researchers did not monitor total caloric or dietary protein intake during the trial.

5. Shoulder Discomfort: One participant withdrew from the fly group due to shoulder joint pain, confirming that extreme fly stretches require sensible load control.

Practical Applications for Your Training

This study indicates that lifters enjoy flexibility when designing programs for chest muscle growth:

• Rotate Exercises Confidently: If heavy pressing irritates your elbows or shoulders, dumbbell flies provide an effective hypertrophic stimulus without sacrificing gains.

• Maintain Full Range of Motion: Ensure the dumbbells descend until your elbows sit level with or slightly below your shoulders to load the pectorals in their lengthened position.

• Match Your Effort Levels: Single-joint flies only build serious tissue when trained with high intensity close to failure. Casual, low-effort sets will not replicate these gains.

• Combine Both Patterns: You do not need an exclusive either-or choice. Programming both compound presses and isolation flies balances overall fatigue and joint stress across a training cycle.

Frequently Asked Questions

Can dumbbell flies completely replace the bench press for chest muscle growth?

Yes, dumbbell flies can replace the bench press for hypertrophy because both exercises stimulate similar increases in muscle thickness when sets approach failure (Dell’Avanzia et al., n.d.). However, the bench press remains superior for building multi-joint pushing strength.

Do dumbbell flies target the inner or outer chest better?

Ultrasound data showed no significant regional differences between flies and presses. Dumbbell flies increased lateral thickness by 17.4% and medial thickness by 14.0%, indicating that the entire sternal pectoral head responds uniformly rather than isolating specific inner or outer borders.

Are dumbbell flies dangerous for the shoulders?

Dumbbell flies present elevated shoulder stress if performed with excessive momentum or loads that compromise joint control. In the study, one participant discontinued due to shoulder pain. Use controllable loads and maintain a slight elbow bend.

Which exercise builds more triceps mass?

The dumbbell bench press stimulates substantial triceps brachii activation because it involves active elbow extension. Single-joint dumbbell flies keep the elbow static, meaning they provide virtually no growth stimulus for the triceps.

References

Dell’Avanzia, F. G., Enes, A., Alves-Marques, F., Costa-Rodrigues, J., Bello, G., Seima, G., Nass, G., Moreira, N. F., Santana, C., Mohan, A. E., Piñero, A., Schoenfeld, B. J., & Souza-Junior, T. P. (n.d.). Dumbbell bench press and dumbbell fly elicit similar pectoralis major muscle hypertrophy in recreationally-trained individuals. Supplied Manuscript.

Varovic, D., Larsen, S., & Grgic, J. (2026). Heavy or light: is muscle fiber growth load-specific? A systematic review and meta-regression. Frontiers in Physiology, 17, Article 1953601. https://doi.org/10.3389/fphys.2026.1953601

Medical Disclaimer

This article is for informational and educational purposes only and does not substitute for individualized medical or physical therapy advice. Always consult a qualified healthcare professional before altering your exercise program or managing joint pain.