###### Abstract
Compared to tensiomyography, which uses uncomfortable electrical impulses to induce muscle contractions, myotonometric devices offer a painless and non-intrusive alternative. This is particularly advantageous for measuring muscle tone in sensitive areas such as the face. Evidence in the literature shows that myotonometric parameters can assess muscle proneness to injury, fatigue, and muscular performance [32; 33; 34; 35]. These compact handheld devices are used to determine the mechanical properties of muscles such as muscle (i) stiffness, the resistance of muscle tissue to external forces, indicative of its intrinsic elasticity; (ii) tone, that is, the continuous, passive partial contraction, highlighting the readiness of muscles for action; (iii) decrement, a measure of muscle endurance against repeated contractions, serving as an indicator of fatigue resistance; (iv) creep, describing the muscle's length change under sustained load and providing insights into the viscoelastic properties of the muscle; and (v) relaxation, which assesses the time needed by the muscle to return to its resting state post-contraction [11; 30]. Despite the growing number of studies collecting data from myotonometric devices, there are only a few studies applying such technology to investigate the muscles that are mostly involved in TMDs, such as the orofacial muscles [7; 9; 27] and the upper trapezius muscle [36; 37; 38]. A recent study found that increased muscle tone can alter masticatory performance in older adults [39]. Moreover, another study reported that malocclusion affects the biomechanical and viscoelastic properties of core stability muscles more than the masticatory ones [40]. [PERSON] et al. [27] found increased masseter and upper trapezius stiffness and tone in subjects with myogenous and mixed TMDs. Interventional studies using myotonometric devices, particularly on limbs, provide foundational insights into the effects of various exercises on muscle tone and stiffness. For example, there is evidence that stretching decreases stiffness in leg muscles [35; 41], while eccentric exercise is known to increase the stiffness of the calf muscles [42]. Extending these insights beyond the limbs, interventional studies investigating myotonometric changes in the masseter and upper trapezius muscles after exercise periods reveal similar muscle response patterns. For example, ultrasound therapy led to a transitory lowering of the myotonometric parameter decrement [43]. [PERSON] et al. [9] found that TMD treatment, which led to a reduced masseter and sternocleidomastoid muscle tone, also augmented jaw opening. [PERSON] et al. found that using lumbar lordosis assistive support lowers the decrement and stiffness of the upper trapezius in subjects with a forward head posture [37]. Moreover, the stiffness of the upper portion of the trapezius muscles was decreased with the ischemic compression of the myofacial trigger points, a six-week programme with stretching, mobilisation, strengthening, stabilisation workout, eccentric exercises, and cervical stretching with craniocertical flexion exercises [36; 38; 44; 45]. Within this context, the primary goal of this study is 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 are designed to (i) mobilise the orofacial and neck muscles and (ii) engage subjects in heavy chewing. Drawing upon existing literature using similar interventions, we hypothesised that the masseter muscle's stiffness and tone, as well as those of the orofacial and trapezius muscles, would decrease as a result of the exercise intervention. Conversely, we hypothesise an increase in stiffness and tone in response to heavy chewing activities.