Manual Muscle Testing of the Thumb

Cervical Spine Fingers (MCP, PIP, & DIP Joints) Knee
Glenohumeral Joint Thumb (CMC, MCP, & IP Joints) Ankle
Elbow & Radioulnar Joints Lumbar & Thoracic Spine Scapulothoracic
Wrist Hip Toes (MTP, PIP, & DIP Joints)
Motion Patient Position Start Position End Position
Thumb Abduction Patient sits with the wrist in neutral, and thumb relaxed in adduction. Therapist stabilizes metacarpals by maintaining wrist in neutral in somewhat of a handshake position. Resistance is applied to the lateral aspect of proximal phalanx in the direction of adduction. Patient lifts thumb toward ceiling against resistance.
Thumb Adduction The patient sits with wrist in neutral, and thumb relaxed and hanging down in abduction. Therapist stabilizes metacarpals by grasping the patient's hand around the ulnar side. Resistance is given on medial side of proximal phalanx in the direction of abduction. Patient adducts against resistance.
Thumb IP Extension The patient sits with wrist in neutral, and the ulnar side of the hand resting on the table. The thumb should be relaxed and in a flexed position. The therapist uses the table to support the ulnar side of the hand and stabilize the proximal phalanx of the thumb. Resistance is applied over the dorsal surface of the distal phalanx of the thumb in the direction of flexion. The patient actively extends the IP joint.
Thumb IP Flexion The patient sits with wrist in neutral, and the MP joint of the thumb in extension. The therapist stabilizes MP joint in extension then gives resistance with the other hand against the palmar surface of the distal phalanx in the direction of extension. Patient actively flexes IP joint.
Thumb MP Extension The patient sits with wrist in neutral, with the CMC and IP joints relaxed in slight flexion. The MP joint is in abduction and flexion. The therapist stabilizes the first metacarpal allowing motion to occur only in the MP joint. Resistance is provided with the other hand on the dorsal surface of the proximal phalanx in the direction of flexion. The patient actively extends MP joint.   
Thumb MP Flexion The patient sits with the wrist in neutral, with the CMC and IP joints in extension. The MP joint is in abduction and in extension. The therapist stabilizes the first metacarpal allowing motion to occur only in the MP joint. Resistance is provided with the other hand on the palmar surface of the proximal phalanx in the direction of extension. The patient actively flexes MP joint.   
Thumb Opposition The patient sits with forearm in supination, and wrist in neutral. The therapist stabilizes the hand by placing the dorsal aspect of his fingers on the palmar aspect of the patient's fingers, and the same with the thumb. Resistance is given on the palmar side of the thumb in the direction of extension. The patient actively flexes the thumb toward the little finger.  

Adapted from:

Hislop, Helen J. & Montgomery, Jaqueline with contributor Barbara Connelly.

      Daniels and Worthingham's muscle testing: techniques of manual examination., 6th edition, 1995.