Why curls build biceps better than rows

When muscle thickness is measured using ultrasound after strength training, differences in thickness between the upper and lower parts of the biceps indicate localized muscle growth, not just temporary fluid buildup.

When you do bicep curls (an isolation exercise), your muscles get a bigger 'pump' right after compared to doing rows (a compound exercise), especially near the top of your arm close to your shoulder.

After 8 weeks of training, dumbbell curls lead to a small increase in muscle thickness near the elbow in the biceps area, while dumbbell rows do not produce a similar change in the distal regions, suggesting different exercises may affect muscle growth in different locations.

After 8 weeks of doing dumbbell rows, the muscles at the back of the upper arm near the elbow show almost no growth, suggesting that this exercise may not effectively build muscle in those specific areas.

After one workout session, dumbbell curls cause more temporary swelling in the upper arm muscles than dumbbell rows, suggesting that the two exercises may trigger different levels of metabolic stress or fluid buildup in those muscles.