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%.

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%).

Doing bicep curls leads to bigger arm muscles (11% growth) than doing dumbbell rows (5% growth) after training for 8 weeks, at least in men who haven't exercised before.

If you want bigger biceps, you should focus on exercises that only move your elbow (like bicep curls) instead of exercises that involve multiple joints (like pull-ups).

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

If young men who have never weight trained before do bicep curls twice a week for 10 weeks, their arm strength increases by about 12% on average.