4 Common Cable Fly Mistakes — And What Exercise Science Says Instead Want to grow your chest efficiently? Then avoid these biomechanical pitfalls that reduce muscle activation: 🔬 1) Arms Too Straight in the Stretch → A fully extended elbow shifts tension away from the pecs and onto the biceps and shoulder joint. ✅ Keep a slight elbow angle (~15–30°) to optimize pec stretch without joint strain. 🔬 2) Elbows Dropping Too Low → When elbows fall below wrist level, tension moves off the chest. ✅ Ke