Lift off test is done to assess the function of -
Lift Off Test (Gerber's test) 

Lift off test is done to assess the strength of subscapularis muscle and detect a rupture of the subscapularis tendon.
Subscapularis functions primarily as an internal rotator of the shoulder
The test is performed with the arm extended and internally rotated such that the dorsum of the hand rests against the lower back.
The subscapularis is maximally active in this position.
The patient is then instructed to lift his/her hand off the back (Lift - off) (Attempting further internal rotation)
If the patient is able to lift the dorsum of the had off the back the subscapularis tendon is intact and the test is considered negative.
If the patient is not able to lift the dorsum of the hand off the back the subscapularis tendon is torn and the test is considered positive.
The lift-off test
is a sensitive and specific test for subscapularis function and this has been validated by electromyography studies.
Supraspinatus
Infraspinatus
Teres minor
Subscapularis