People between 21 and 65 years of age with the following characteristics may be eligible for this study: 1) no neck pain or trigger points in either upper trapezius muscle; 2) no neck pain but a latent trigger point in at least one upper trapezius muscle; or 3) neck pain of less than 3 months' duration and an active trigger point in at least one upper trapezius muscle. Participants undergo the following procedures: