Representative EMG amplitude data from two subjects (A and B respectively).

<p>Each line represents the integrated EMG activity for each movement direction, and data is interpolated between directions for representation. Data is normalized with respect to the maximal value between BASE and PAIN for each muscle. Note the consistent decreased activity for the injected muscle (right splenius capitis) for both subjects but the variable change for the other muscles. For instance, the right upper trapezius (RUTR) shows reduced activity in the painful condition for Subject A but increased activity for subject B. (Right–R and Left–L: Sterno Hyoideus–HYO, Sternocleidomastoideus-STER, Anterior Scalenus-SCA, Splenius Capitis–SPL, Upper trapezius-UTR, Lower Trapezius-LTR).