## 4 Discussion  
The aim of the present study was to investigate the changes in muscle tone and the biomechanical and viscoelastic properties of the masseter and the upper trapezius muscles, as assessed by myotonometry, following two distinct guided exercise interventions. These interventions were designed to (i) mobilise the orofacial and neck muscles or (ii) engage participants in heavy chewing. In the present study, we observed an increase in the stiffness and tone of the masseter muscle following the Exercise intervention, contrasted by a decrease in both parameters after the Chewing intervention. The observed changes contrast with previous studies [7,9,27], thus contradicting our hypotheses. We had anticipated that the Exercise intervention, which included stretching and mobility exercises, would decrease both stiffness and tone, while the Chewing intervention, which can be compared to strength training, would lead to an increase in these parameters. However, the stiffness of the masseter muscle increased after the Exercise intervention, which was contrary to our expectations. This increase might be attributed to the exercise protocol inducing a higher blood flow, like a warm-up effect, rather than solely providing the stretching benefits typically associated with decreased muscle stiffness [33]. Similarly, the increase in tone following the Exercise intervention suggests a complex interplay of factors beyond simple mobilisation, potentially involving enhanced muscle temperature and performance improvements, as seen in other studies on muscle rigidity. [PERSON] et al. [55], for example, reported an increase in the stiffness of the thigh leading to a boost in jumping performance after a 10 min cycling workout. In another study, manual therapy induced a similar increase in muscle tone in gastrocnemius muscle [56]. Conversely, the decreased stiffness and tone after the Chewing intervention might be due to a fatigue-induced decrease in muscle contraction capabilities. Although we could not monitor the biting force in this study, we can speculate that the decrease in stiffness after the Chewing intervention happened due to a loss in muscle contraction capabilities and, consequently, a reduction in biting force. If this is true, the results of the present study are in line \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Exercise**} & \multicolumn{3}{c}{**Chewing**} \\ \hline
**Group** & & **PRE** & **POST** & **\%/Sig.** & **PRE** & **POST** & **\%/Sig.** \\ \hline \multirow{3}{*}{Masseeter m.} & Stiffness & 364.03 \(\pm\) & 416.67 \(\pm\) & 14.46\% *** & 414.16 \(\pm\) & 377.64 \(\pm\) & \(-\)8.82\% *** \\  & (N/m) & 64.05 & 98.76 & 118.66 & 101.74 & \\  & Relaxation & 16.29 \(\pm\) 3.04 & 14.44 \(\pm\) 3.29 & \(-\)11.36\% *** & 14.53 \(\pm\) 3.79 & 15.98 \(\pm\) 3.62 & 9.98\% *** \\  & (ms) & 16.65 \(\pm\) 2.00 & 17.82 \(\pm\) 2.30 & 7.03\% & 17.71 \(\pm\) 2.37 & 16.73 \(\pm\) 1.94 & \(-\)5.53\% \\  & Creep (a.u.) & 1.03 \(\pm\) 0.18 & 0.93 \(\pm\) 0.20 & \(-\)9.71\% *** & 0.93 \(\pm\) 0.23 & 1.02 \(\pm\) 0.22 & 9.68\% *** \\  & Decrement & 1.87 \(\pm\) 0.21 & 1.87 \(\pm\) 0.34 & 0\% & 1.79 \(\pm\) 0.38 & 1.79 \(\pm\) 0.35 & 0\% \\  & (a.u.) & 387.45 \(\pm\) & 379.27 \(\pm\) & \(-\)2.11\% & 365.61 \(\pm\) & 350.01 \(\pm\) & \\ Trapezius m. & (N/m) & 69.67 & 79.32 & \(-\)2.11\% & 65.63 & 42.50 & \(-\)4.27\% \\  & Relaxation & 14.62 \(\pm\) 2.50 & 14.88 \(\pm\) 2.72 & 1.78\% & 15.24 \(\pm\) 2.48 & 15.67 \(\pm\) 1.74 & 2.82\% \\  & (ms) & 19.18 \(\pm\) 2.56 & \(-\)7.65\% *** & 18.86 \(\pm\) 1.90 & 18.66 \(\pm\) 1.82 & \(-\)1.06\% \\  & Tone (Hz) & 20.77 \(\pm\) 2.95 & 19.18 \(\pm\) 2.56 & 2.20\% & 0.95 \(\pm\) 0.15 & 0.98 \(\pm\) 0.10 & 3.16\% \\  & Creep (a.u.) & 1.21 \(\pm\) 0.27 & 1.07 \(\pm\) 0.19 & \(-\)11.57\% *** & 1.04 \(\pm\) 0.08 & 1.05 \(\pm\) 0.12 & 0.96\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Descriptive statistics of myotonometric parameters. Data are expressed as the mean \(\pm\) standard deviation.