This is one of the very best bang-for-your-buck exercises for increasing strength and muscle mass while also maintaining and even enhancing mobility through the shoulders and back. As anyone who's tried to stretch a fully pumped muscle knows, this is not a comfortable feeling. That said, this isn't for beginners.
Neutral-Grip Lat Pulldown, Accentuated Eccentric
The neutral grip allows the lats to increase their range of motion into a stretch at the top of the movement while also helping the shoulder complex stay in a more centrated position. Both variables are great for longevity, orthopedic health, and muscularity.
Rock back a little in this exercise to create almost a high-row angle on the concentric (pulling) portion of the exercise, then come back and normalize your torso position into neutral. Bring your head forward to really stretch through the eccentric (negative) portion of the exercise.
If you master this movement, get a partner to force the eccentric by pressing down on the weight stack as you slowly let your hands and arms move up into a straightened position. (See video.) If you're a sicko who loves the pain, add a 10-30 second forced stretch out of this exact position while maintaining neutral shoulder alignment and stretching through the lats.
This will stick a fork in your workout, so program it on the tail-end of an upper body or back-emphasized training day.