Previous studies have shown that peripheral muscles weakness or inhibition is related to spinal disorders. Passive mobilization and manipulation are likely to reverse such muscle weakness for patients with spinal pain. The purpose of the study was to assess the effect of spinal mobilization on the maximal muscle strength of the shoulders.

Participants without existing neck pain or shoulder problem will be recruited. Subjects will be screened by 2 investigators independently for shoulder muscle weakness. Weakness is determined by the strength of the other side when one side is remarkably weaker or by comparing with the general strength of the deltoid muscle if both sides are suspected involved.

Suitable participants will undergo shoulder strength testing with a handheld dynamometer. Participants will be divided into the intervention group and the control group randomly. The shoulder strength will be tested by the second, individual blinded assessor.

Subjects in the intervention group will receive passive spinal mobilization at cervical 4-5 segment on the involved side(s); the control group will receive placebo intervention.

Each participant will be tested for 2 times, before and immediately after a C4-5 joint mobilization on the involved side (s).

Inclusion Criteria:

• Healthy adults

Exclusion Criteria:

• People with active neck or should pain