Summary
Jeff Cavaliere of AthleanX argues that the chest fly is a largely ineffective and potentially dangerous exercise for chest development. Using a rubber band to illustrate muscle fiber direction, he explains that the stretch felt at the bottom of a fly movement comes from the coracobrachialis, not the pec major. He promises a follow-up video showing how to train the upper chest using only a flat bench.
Key Points
- The chest fly is considered a waste of time for building the pec major, despite being widely used by gym-goers focused on chest development.
- The pec major originates along the sternum and inserts at the outer portion of the upper arm bone (humerus); its fibers run horizontally across the chest.
- During a fly movement, the relative distance between the pec major’s origin and insertion does not change significantly compared to a bench press — meaning no meaningful additional stretch is placed on the chest muscle.
- The deep stretch felt at the bottom of a fly is actually tension on the coracobrachialis, a muscle running from the coracoid process (deep in the shoulder) down to the upper arm — not the pec major.
- Because the coracobrachialis is being loaded — not the pec — the chest fly does not provide superior chest activation despite feeling more intense.
- Going deep into a fly position increases the risk of shoulder injury, including pec tears and AC joint damage, without delivering added chest development in return.
- All pressing movements are recommended as the more effective and safer choice for building the chest.
Exercise Details
Chest Fly
- Target muscles (intended): Pec major
- Actual primary stretch: Coracobrachialis (not the pec major)
- Common mistakes to avoid:
- Assuming a deeper range of motion increases pec muscle stretch — it does not
- Lowering arms below the body’s natural plane, which stresses the shoulder joint without benefit to chest development
- Using the fly as a primary chest-building movement
- Recommendation: Avoid for chest development purposes; the exercise creates injury risk with minimal chest-specific stimulus
Bench Press (referenced for comparison)
- Target muscles: Pec major
- Form cues:
- Do not lower the bar below the chest plane to avoid shoulder joint stress
- The pec major’s origin-to-insertion relationship is appropriately loaded throughout the press movement
- Recommendation: Preferred over flies for chest hypertrophy