I'd always suggest doing pull-ups with thumb around the bar for safety reasons.
Lat pull downs are a different story and keeping your thumb in front of the bar is helpful to keep you from pulling less with your biceps.
Think of "pulling from your elbows" until you feel your shoulder blades meet
Lat pull downs are a different story and keeping your thumb in front of the bar is helpful to keep you from pulling less with your biceps.
Think of "pulling from your elbows" until you feel your shoulder blades meet