## 4 Discussion  
Our main results indicate that a 3 week manual manipulation intervention over a pre-selected cervical level reduces pain and disability and induces a positive change in the patient's global impression of change in young adults with nonspecific neck pain. Our results are in agreement with previous studies showing that a multisession program with manual manipulation reduces pain and improves function in both cervical [8] and lumbar regions [15] compared with pharmacological and instrument-assisted manipulation approaches, respectively. Although the pain-relieving mechanism of spinal manipulation has not been clearly determined, it was proposed that the activation of the descending inhibitory pain mechanism might play the most important role concerning post-manipulation hypoalgesia [38]. It should be noted that in the present study, positive results in pain and disability were found with a non-specific region manipulation, suggesting that the clinical effects occur regardless of a previous assessment of tender muscles or restricted spinal levels, as is usual in clinical practice and previous research [15; 34; 36]. Although only evaluated at a short-term level, no differences were observed in pain intensity and pressure pain threshold between region-specific versus non-region-specific manipulation techniques in patients with chronic low back pain [14]. The results obtained at long-term level in cases of low back pain seem to also corroborate our results since no differences were obtained between prescritively selected manipulation and a therapist-selected approach [39]. It seems that the positive results observed were not necessarily related to the \"correction of the vertebral dysfunction\" but may be a result of the spinal manipulation itself. If confirmed in future studies, it could challenge the concept that a specific approach to the spinal segments would explain the reductions in pain intensity that are experienced by the patients. Therefore, the act of manipulation may be more important that the level where it occurs. The pressure pain thresholds and pressure pain perception did not change immediately after the first session, but only after three sessions, for the manual manipulation and placebo groups. The changes were present not only on the upper trapezius, but also on both biceps \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **Manual** & **Placebo** &
\begin{tabular}{c} **Instrument-** \\ **Assisted** \\ \end{tabular} & **Control** & \(p\) **Value** \\ \hline Muscle Properties & & & & & \\ \hline Tone (\%) & & & & & \\ right upper trapezius & \(0.72\pm 6.17\) & \(-0.25\pm 9.22\) & \(-3.61\pm 2.44\) & \(-0.22\pm 0.68\) & \(0.465\) \\ left upper trapezius & \(5.12\pm 9.35\) & \(-2.27\pm 10.45\) & \(-3.64\pm 1.57\) & \(-0.38\pm 1.00\) & \(0.088\) \\ right biceps brachii & \(1.24\pm 5.99\) & \(-3.90\pm 3.88\) & \(-2.09\pm 1.70\) & \(-0.43\pm 1.51\) & \(0.066\) \\ left biceps brachii & \(-3.81\pm 6.93\) & \(-1.96\pm 4.50\) & \(-2.17\pm 2.79\) & \(-0.45\pm 1.46\) & \(0.554\) \\ Elasticity (\%) & & & & & \\ right upper trapezius & \(0.71\pm 12.60\) & \(-9.33\pm 8.96\) & \(5.54\pm 5.90\) & \(1.51\pm 5.77\) & \(0.059\) \\ left upper trapezius & \(5.65\pm 11.19\) & \(-6.92\pm 14.34\) & \(4.59\pm 4.45\) & \(2.34\pm 6.18\) & \(0.067\) \\ right biceps brachii & \(0.22\pm 10.09\) & \(-2.50\pm 11.30\) & \(1.41\pm 7.65\) & \(-1.08\pm 2.96\) & \(0.830\) \\ left biceps brachii & \(-1.54\pm 10.46\) & \(5.03\pm 15.58\) & \(0.97\pm 7.40\) & \(-0.27\pm 3.43\) & \(0.612\) \\ Stiffness (\%) & & & & & \\ right upper trapezius & \(3.15\pm 9.53\) & \(2.51\pm 20.35\) & \(-4.49\pm 6.61\) & \(1.22\pm 3.52\) & \(0.563\) \\ left upper trapezius & \(7.38\pm 13.83\) & \(-4.78\pm 17.78\) & \(-5.40\pm 2.78\) & \(-3.13\pm 3.91\) & \(0.106\) \\ right biceps brachii & \(4.43\pm 9.43\) & \(1.28\pm 8.67\) & \(-7.23\pm 8.98\) & \(-0.28\pm 7.80\) & \(0.052\) \\ left biceps brachii & \(-2.17\pm 8.98\) & \(1.64\pm 4.92\) & \(-8.94\pm 7.24\) & \(-1.42\pm 3.64\) & \(0.068\) \\ \hline \hline \end{tabular}
\end{table}