Wide grip pullups involve shoulder adduction
, while close grip pullups involve shoulder extension
. The rear deltoid is a synergist in shoulder extension but not in shoulder adduction. Otherwise, the same muscles are involved in both movements, though at different angles.
For most people, extension is a stronger movement than adduction
The pronated (palms away) grip puts the biceps at a mechanical disadvantage in flexing the elbow, while a supinated (palms facing) grip puts them at an advantage. A neutral (palms facing each other) grip, some allege, is the best grip for training all of the elbow flexor muscles.