your weight pull up refer to:
1) hanging weight from your waist
2) weight assisted pull up.
In 1 and 2, try not to relax your joints, maintain a slight
tension in your joints ( a bit bent).
Relax the joints, would transfer the force directly to the
attached tendons, tearing it.
In the latest research, weighted pull up is really not
recommended as it seems to damage the shoulder. It would be better
to use your bodyweight and increase the rep. (gymnast has
build superior back just his own body weight)
You can increase your
reps like up to 20 rep per set and do 6 - 10 sets to build massive
back without hurting the joints.