Doing both compound movements like pull-ups and isolation exercises like dumbbell curls is the best way to build bigger biceps and the underlying brachialis muscle.

Isolation exercises targeting a single joint (e.g., leg extensions) produce greater hypertrophy in bi-articular muscles (e.g., rectus femoris) compared to multi-joint compound movements (e.g., squats) due to avoidance of active insufficiency.

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.

When people want to build bigger biceps, they should focus on bicep curls rather than compound movements like pull-ups that work multiple muscle groups at once.

Compound exercises involving greater total muscle mass do not produce superior hypertrophy in target muscles compared to isolation exercises when training volume and effort are equated.