To stop those back muscle gains slipping away, I recommend getting around 8 sets at least a week.
The back isn’t a single muscle; it’s made up of many muscles. The back makes up two-thirds of your torso, so way more focus needs to be put on back training over mirror muscles like the chest.
Most lifters are around 10-12 sets a week of direct back work to make gains. The sweet spot for most lifters is around 16-20 sets. That wants to be split evenly across vertical and horizontal pulling exercises.
WHAT TYPE OF EXERCISE?
+ VERTICAL
Overhand Pulldown
Parallel Chin Ups
Underhand Pulldown
+ HORIZONTAL
Cable Row
Bent-Over Row
Chest Supported Row
FREQUENCY
Because the back can handle a pretty good beating, up to 20 sets a week, I recommend splitting that across two sessions a week otherwise you risk running into serious recovery problems.
RANGE OF MOTION
Ensure you fully shorting the muscles and reaching peak contraction. Prevent using excessive momentum, which is usually coming from the legs by swinging hips backward and forwards. That girl isn't impressed by how much your lifting, she will likely be impressed when you build some muscle, so start lifting properly "Leave the ego at home."
So, the next time on the lat pulldown lower the weight and pull the bar all way to your chest and without excessively leaning back.