After 8 weeks of training, dumbbell curls lead to a 11% increase in muscle size near the elbow compared to dumbbell rows, which result in only a 1% change, suggesting that exercises involving a single joint may produce greater muscle growth in the distal part of the muscle.

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 8 weeks of weight training, the upper part of the biceps grows more with both dumbbell curls and rows, while the lower part grows more with curls than with rows, indicating that different parts of the muscle respond differently to different exercises.

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.

When untrained adults want bigger biceps, doing simple curl exercises works better than doing rows that use multiple muscles at once.

When men who hadn't trained before did bicep curls (a single-joint exercise) for 8 weeks, their arm muscles grew about 11%. But when they did dumbbell rows (a multi-joint exercise) instead, their muscles only grew about 5%.