After one workout, dumbbell curls cause a larger temporary increase in muscle thickness near the elbow compared to dumbbell rows, which may reflect differences in how much the muscles are activated or how much metabolic stress they experience during each exercise.

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.

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 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 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.

When untrained men do arm curls for 8 weeks, their biceps get thicker (about 11%). But when they do dumbbell rows instead, their biceps only grow about half as much (about 5%).